• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer
  • About this Site
  • E-Booklets
  • Shop
  • Resources
  • Consulting

My Chemical-Free House

A Guide to Creating a Healthy Home

  • Healthy Building
    • Insulation
    • Windows & Window Treatments
    • Glues & Caulks
    • Grout & Mortar
    • Drywall
    • Drywall Mud & Wall Texture
    • Showers
    • Doors
    • Pressed Wood Products
    • Sheathing & Subfloor
    • Siding/Cladding
    • Pipes
    • Alternative Building Systems
    • Building for the Chemically Sensitive
    • Non-Toxic Prefabs
    • How to Test Materials
  • Healthy Interiors
    • Flooring
    • Gym Flooring
    • Flooring Underlayment
    • Mattresses & Bedding
    • Sofas & Furniture
    • Leather Furniture
    • Desks and Chairs
    • Kitchen Cabinets
    • Countertops
    • Sealers
      • Paint
      • Mineral Paints
      • Linseed & Tung Oil
      • Natural Wood Pigments
      • Natural Plaster
      • Natural Countertop Sealers
      • Concrete Sealers
      • Wood Finishes
    • Bathroom
    • Rugs
    • Wallpaper
    • Lead Free Faucets
    • Cookware
    • Kitchen Appliances
    • DIY Sofa
    • Heaters
    • Reduce Flame Retardants
    • Reduce New Home Offgassing
    • Reduce Fragrance & Smoke
    • Air Purifiers for VOCs
    • Cleaning Products & Air Fresheners
    • Personal Care Products
    • Green Certifications
    • Gift Guide
  • Tiny Homes and Trailers
    • List: Simple Homes & Shelters
    • List: Trailers & RVs
    • List: Emergency Housing
    • Cargo Van Conversion
    • All Metal Tiny Home
    • Simple Insulated Shelter
    • All Aluminum Travel Trailer
    • Cargo Trailer Conversion
    • Teardrop Trailer
    • Tiny House Systems
    • Flooring for Vans, Trailers
    • Composting Toilets
    • How to Offgas a New Car
    • Building for Chemically Sensitivity
  • Mold-Free Building
    • The Causes of Mold in Tiny Houses
    • A Detailed Mold Preventative Build
    • How “High Performance” can Help Prevent Mold
  • Mold-Free Interiors
    • Mold Testing Overview
    • Air Purifiers for Mold
    • Ozone to Kill Mold
  • Mold Avoidance
    • Decon your Car
    • Camping Gear
    • Planning a Sabbatical
    • Traveling with Environmental Sensitivities
    • Locations Effect Ebook
    • The Locations Effect – Canadian Locations
    • The Locations Effect – Caribbean Campsites
    • Interview: Healing MCS with Mold Avoidance

mold free building

17 Non-Toxic Eco Prefab Homes Compared | 2021

February 4, 2020 by Corinne 9 Comments

how to build a healthy prefab, what to look for

This list focuses on healthy non-toxic prefabricated (“prefab”) homes. They must be both mold-preventative designs and low VOC to be healthy homes.

I have reviewed them myself with input from customers and building science experts. Many need further inspection.

When considering a prefab, it’s important to see the detail design of the build, tour the factory (or have an expert tour it), see pictures of their builds in progress, and if possible tour a home that is already built by them.

They must be willing to work with a mold aware architect. Some companies have their network of installers and some rely on you having your own builder. Many will turn down severely chemically sensitive clients; I recommend bringing me onto the team before getting into materials with them to avoid that scenario.

Before digging into the reviews of 17 “green” prefab companies, we are going to look through what you need to know about the process of building prefab and make sure the materials are safe and the design is mold preventative.

Building a home, even if prefabricated partially or fully offsite, is still a complicated process to navigate. Please get in touch for help going through the process of choosing materials and negotiating with all the different players.

This post contains no sponsored or affiliate content, and I don’t have a partnership or other ties to any of the companies listed.

Steps to Building a Healthy Prefab

800
  1. See the list below for some prefabs that I have prescreened, or start with one you like.
  2. Screen the prefab design for initial clues into its quality, including any errors in the photos (do an initial review with someone who knows building science). See the list of good signs and red flags below.
  3. Get sufficient photos and schematic details of the design of the build (walls, ceiling, floors). Take them to a qualified building science expert like Cheryl Ciecko.
  4. Tour the factory and a home they have built. Talk to others who built with them. Look for reviews of the company.
  5. Talk to the company more seriously to gather more details about the plans if you didn’t get them in step 3.
  6. Get your specific house plans reviewed by at least two qualified building science experts, including the architect that you have hired independently. Plans are made specific to your climate and piece of land.
  7. I recommend bringing on an HVAC consultant to your team, too, to size and spec (or review) the HVAC, including the ventilation.
  8. Bring a builder on board early in the process of design to make sure they are part of the team. (Some companies have builders or work with a network of builders, if that is the case, vet them to see if they are good.) The builder needs to be really good and that’s not easy to find. Make sure that is in place early.
  9. You or someone with building knowledge should supervise the preparation of the land, the foundation, and the install of the shell or modular unit. Supervise all the stages of the build.

Good Signs and Red Flags

  • The age of the company is important to me. They should not be on their first prototypes. Ideally, you should be able to see some of their houses that are at least 10 years old. You should feel confident in the person running the company. They need to be in business (in the future) to honor warranties. There are two good companies, however, on this list that are less than 10 years old (Ecocor and GO Logic).
  • A company without architects or building science experts on the team needs to be looked at more carefully. Who is in charge of the design and how knowledgeable are the project managers? Steer clear of any company that doesn’t promote their building science expertise.
  • If the company provides the General Contractor or works with a network of general contractors, vet them just as carefully. If you don’t have enough choice in who you use to build it out on-site, you won’t get a well-built house.
  • While you should expect to make minor changes to the design with your architect as a consultant on the team, any major design flaws in their models is a red flag.
  • Talk to someone who built with the company recently. If the company is disorganized and the project manager could not coordinate all teams well, that’s going to be a huge mess. Things might not get done right due to this problem (which is a common one with prefabs).
  • I look for the ability to tour the factory—ideally the company owns the factory—and make sure you see a house that is built. Even better if it’s a hotel or Airbnb you can stay in.
  • You need to be able to see details of the building systems/designs system before committing any substantial amount of money.

Pros and Cons of Building Prefab

Benefits to Building Prefab

  • Mistakes are limited in the really good factories—computer planning, precise cuts, fabrication by machines, and panels put together by highly trained technicians limit mistakes that are extremely common in traditional builds.
  • Build out of the rain—the wood and other components are stored inside and stay dry (in theory, if it’s a good company). The panels or modules will be built in a climate-controlled factory. It goes up faster on-site, during a dry time, and should be watertight before it rains.
  • Enjoy cost savings—it would be very expensive to build a house at as high of a quality as some on these on this list from scratch, with high-quality craftmanship like that accomplished in the factory. If you go with a predesigned layout (not custom), prefab helps you save even more. With many companies, you may also have a more fixed price than in a conventional build where many things tend to change.
  • It’s faster—the whole process from start to finish is likely to be faster than with a conventional build.
  • There’s less work for you — while you do have to tour the factory and have the plans reviewed by an architect, you don’t have to supervise as many parts as in a conventional build. Wall and roof panels, and in some cases whole modules, will all be done in the factory setting and, if the factory is good, it’s likely to be done very precisely and correctly. That is almost never the case on-site at a conventional build. Since most homeowners don’t have the knowledge to supervise a build, this can be essential.

Downsides to Building Prefab

  • Have less control—while it might be possible to be in the factory during the manufacturing of your specific panels, you don’t have full control here over supervision in the same way you would on-site.
  • If you are extremely sensitive, you need to have confidence in the factory that they are only using clean wood, stored correctly, etc. (The same goes for all the components, but with the wall systems the wood is clearly the most important part).
  • Ability to analyze and review/change the plans—with some companies, you cannot see the full details of the plans (or the walls, ceiling, floor system) until you put a deposit. This is a huge problem. The good companies do show their designs.
  • Some companies will not allow you to bring your own architect as a consultant on the plans (though most will). That would be a deal-breaker for me.
  • Supervision is still needed—assuming you were able to have your plans reviewed by multiple experts, and feel confident in the factory making the panels or prefab, you still have a fair amount of planning and supervising on-site, making sure the local team knows how to put this together properly, that the foundation is detailed right, the land was prepared properly, and the final on-site details (like the roof) are done right.
  • On the topic of supervision, if the prefab is a very unusual system, it becomes more difficult to have it confidently reviewed and to supervise it.
  • Possible lack of coordination between teams—with some companies that don’t have a strong process in place and strong project managers, and/or if your builder is not on board from the start, you may have a lot of difficulties arising between the parties, with no clear person/company responsible when things go wrong.
  • Prefabs aren’t typically inspected in the usual way—they are inspected in sections, and the companies have individual agreements with the states to allow them to do “inspections” out of state and/or off-site. When the local inspector checks in order to give you a certificate of occupancy, they are only checking things at the finished level, not the construction level.

Building with Environmental Sensitivities

800800

If You Have Chemical Sensitivities

  • Other things I look for is to make sure I have control over the finishes in a way that suits your environmental sensitivities or your degree of toxin avoidance.
  • You should have control over: flooring types, all wood finishes, all sealers, all paints, some glues, the shower system, the cabinet company, and the countertops. This is where you want to know how customizable they are (usually very).
  • Elements that are fixed are likely: framing type, insulation, flashing tapes, house wrap/WRB, and possibly window and door types. With these, you want to know if you can tolerate the materials specified. In general, don’t try and alter the main components. Though there might be a little bit of choice here, for example, with the window framing material.
  • With most companies, you have a choice with the siding and roof types.
  • Some of the best companies are reluctant to work with someone super chemically sensitive. Sensitive customers can demand changes that compromise the integrity of the build; a good company won’t allow this and won’t want to deal with it. Bring me onto the team early in the process, possibly before you speak to them. I can work with the whole team to make sure you get products that are healthy for you and they don’t compromise the building system.
  • Prioritize QUALITY over extreme modifications to make something perfect. It’s better to have to wait for your house to offgas, and have a house that will last a long time, than the other way around. Many people are making this mistake – building something too modified for chemical sensitivities that will go moldy and not get them out of the toxic loop.

If You Have Mold Sensitivities

  • The design of the prefab system is the most fundamental part that needs to be done right.
  • Inspection of the factory to see how they store materials is important.
  • Bring your own architect on board, even if just as a consultant. Make sure the designs are solid (reviewed by more than one building science expert) and the final design for your climate and land is solid.
  • Bring your own HVAC consultant to review the system.
  • You need an excellent builder.
  • You need supervision of all parts of the build.
  • You need to know which party is taking responsibility for each part that could go wrong.

If you are interested in how to build mold preventative homes, join my mailing list where I share courses and other educational materials that will help you to manage and supervise your build.

Thank you!

You have successfully joined our subscriber list.

Definitions: Prefab, Manufactured, Mobile, Kit, and Modular Homes.

Prefab (Prefabricated)—This is the general term for all of these building types that are made partially or fully offsite:

  • Panelized Prefabs—Panelized construction is the most appealing type to me. The exterior walls and ceiling pack onto a truck and are usually assembled with a crane. Some have windows and doors installed at the factory (most of the ones I looked at do), while others have those parts installed on-site.
  • Manufactured and Mobile Homes—I don’t cover these types in the post. Manufactured homes are usually the type of prefab that is in mobile home parks, and are not usually good quality. Mobile homes are homes on wheels (including tiny homes on wheels) and are covered in this post.
  • Modular—Modular homes are more complete than panelized. Modules or boxes are built in the factory and wrapped and taken by a flatbed truck to the construction site. There might be just one module for a small house or many modules that fit together. They are lifted by a crane and set on a foundation. Some modular homes are almost complete when they arrive and others are finished on site.
  • Kit Houses—With a kit home, all of the materials for the house are built in the factory, numbered, and shipped to the site. A kit home doesn’t come with walls or a whole module built (or partially built). Instead, it comes with all the materials you need to build the house, stacked up, and labeled.

Review of 17 Non-Toxic Prefab House Companies

1. Bensonwood Passive Homes

https://www.instagram.com/p/BrnztsHnkTD/

Bensonwood is at the top of my list because it is the most established company making well made Passive Houses (and other types). They are well detailed for mold prevention, made in a factory that they own.

They came to my attention because the builder Matt Risinger toured their factory and worked with them. You get to see a bit about how one of their models are made in this video. This is the house made by Matt Risinger’s company (which you can see during the house tours Matt puts on).

You can tour the factory yourself, too.

This is a panelized custom prefab. The walls and ceilings are made in the factory and they go up on-site at a dry time of year in one to two weeks. The houses can be built to Passive House standards and they use timber frame construction.

Build Type Options

They have three ways to build:

1) Bensonwoods fabricates the custom-designed shell and installs it (this includes the walls, roof, floors, windows, and door). Your builder does the rest of the finishing, as well as the foundation and site prep.

2) The enhanced shell option includes the shell plus some prefabricated components, such as window casings, stairs, and doors (you can see these options on the website).

3) The whole house option, where the house is completed by one team.

Geographical Area

The whole house option is a finished house, but it is only available in the area around Walpole, New Hampshire. The other options can be shipped to 49 states.

Design & Materials

A typical Bensonwood wall panel would have a service cavity that may or may not be insulated, then an airtight layer of OSB, then a structural framed wall of I-joists or sawn lumber.

The exterior sheathing might be OSB (typically, Huber’s Zip) or a continuous layer of wood fiber insulation. Cavity insulation is dense-packed cellulose. 

Roofs are made with either EPS or dense-packed cellulose.

See my posts on pressed wood products and insulation to see if these materials would work for your sensitivities.

Windows are Marvin Integrity, Unilux, or Wasco. My window post reviews the toxicity of window types.

The wall and roof systems can be seen on their website. It’s important that they do show the wall designs, so they can be evaluated.

Factory. The panels are made in their own factory, called Tektoniks, in New Hampshire.

Established. They have been in business since 1973. They have been building in this factory since 2000.

Build time. The shell goes up in one to two weeks. The typical time frame from 3-D model to construction completion is 5-10 months.

The Process. It is important to have secured your land before developing any formal plans (as with any good prefab company). Decide between the shell, enhanced shell, or whole house package. They take the design and create a 3-D model and then send that to be fabricated in the factory.

Here is a video of their process of installing the shell.

2. Their Sister Company Unity Homes

https://www.instagram.com/p/BcvKRTElubm/

This is the more affordable wing of Bensonwood that was started in 2012. The models are predesigned, as opposed to the custom Bensonwood designs. However, you can still mix and match some of the elements to make the house more personalized.

The houses’ designs range from 500–3000 sq ft. I love that they took high-end wall panels and made them affordable by keeping it to predesigned packages. The smallest house is $150,000. If you want an affordable prefab, go with predesigned.

The models can be made to Passive House standards.

Design and Materials

This company is a sister company of Bensonwood, using the same technology. The panels are manufactured in the Tektoniks factory.

Most of the clients they build for are sensitive, a representative said. You can bring materials home to test them.

The interiors are very customizable.

Just like Bensonwood, they use the same high-quality mold preventative design, airtight builds, and balanced ventilation (air exchange).

Geographical area. New England is easiest, but they can serve a larger area.

Factory. They have factory tours (the same factory as Bensonwood) in New Hampshire. They also have a show house in New Hampshire.

Process

Just like Bensonwood, they offer three options: the shell, the shell with some finishes (both of these completed by your GC), or the completed house, which is only possible local to their site in New Hampshire.

In the most simplified process, you can choose one of the interior collections, including finishes, in its entirety. This is the fastest and least expensive way to do it.

They also have “Personalized” and “Semi-custom” design paths, in which you can substitute choices from outside the collections. If you would like the interior design to be completely customized, they recommend that you go with the Shell Package and you can finish the interior with materials and fixtures locally.

3. EcoCor Solsken Passive Houses

https://www.instagram.com/p/BfMaqHejHdq/

Another panelized Passive House prefab is at the top of my list. Passive House design is focused on well built, well-sealed, moisture preventative design. And this one is certified as well as vetted by well-respected building science experts.

I have heard feedback from three professionals about this house, and they were all positive regarding the design.

What I have heard is that the product is well-made and the knowledge and experience of the team are on point. The management may or may not be great, depending on who is working there.

Materials and Design

They use healthy materials and they minimize the use of paint, varnishes, and formaldehyde to near-zero VOC, they say.

They use the Zip system, with the Zip OSB layer close to the interior (it will offgas to the interior).

Dense-packed cellulose is used in the exterior wall assembly and Rockwool in the interior service wall. No spray foam insulation.

The bulk of their insulation is on the outside. They do not have sheathing on the outside. They use a WRB to hold in the insulation (under the siding).

Moisture-management

Detailed modeling of plans is done in WUFI software—this is a way to model how moisture moves and could condense in the walls/ceiling/floors. They used moisture monitors in walls of early houses to verify this.

Essentially, they use “out-sulation” (exterior insulation), with a very dry-able (breathable) exterior assembly.

They use mechanical ventilation (HRV).

It’s an excellent design, with knowledgeable team members.

Factory. They manufacture their panels in their own small facility: the Ecocor’s facility in Searsmont, Maine. You can tour the factory.

Here is a video tour about the company.

Geographical Area. Ecocor’s custom designs are delivered anywhere in North America. Check with them about the predesigned models.

How long have they been in business? Ecocor started around 2012, with the Solsken branch of designs launched around 2017.

Costs. One of their 2 bedroom, 1192 sq ft models is about $408,000.

It sounds like they tend to work for upscale houses only (which is not uncommon when you find a really good builder or system, since good quality costs more). This tends to be more expensive than BrightBuilt or Gologic.

This is not your budget option, but it’s not overpriced either if what you want is quality.

4. Morton Metal Siding Structure

https://www.instagram.com/p/Bvb4gS2gM68/

This company makes fairly standard construction metal siding homes and structures and have been reviewed by Cheryl Ciecko. They have worked with her and they are willing to work with her again to make sure it’s designed right.

Process

With the Morton process, many materials are manufactured in their plants (which they own—this is a large company). Building components are shipped to the job site using their trucks. Construction is executed by their construction crews—vet your local crew well.

Construction management is provided by them—again, vet the local management well. This is a design-build firm, which means they take care of the whole process.

They use Allied Design Architectural & Engineering Group, but they will allow your architect to have input on the plans.

Design & Materials. This is a conventional build; it’s not high performance or Passive House. It’s stick framing, regular insulation, metal siding, and drywall. There’s nothing especially unique here other than they are willing to work with Cheryl.

Established. It’s a well-known brand, around since the 1940s with a robust warranty and little risk of the company going out of business soon.

Factory. They are fabricated in Morton, IL.

5. Holz100 All Wood Houses

https://www.instagram.com/p/Bz-y6YYjJl3/

This panelized and module prefab is something a little different. This company makes panels that are made from all wood: walls, ceiling, and floors. No adhesives. No nails. Just wood. Siding and roofing materials might not be wood.

They claim a 50-year warranty on condensation and mold in the walls. The company has not been in business for 50 years though, about 25 so far.

The next step here would be to see if a building science expert (actually, more than one) can look at this wall system, which is a series of pieces of wood with some air gaps, and see what they think about moisture management in that type of wall.

I would also like to see computer modeling of moisture in the walls, and why it doesn’t hit dewpoint in those spaces, or real-life data from the company showing how moisture performs in the walls.

I want to know how they deal with the roof, since it looks like they are putting an exterior vapor barrier on the flat roofs that could get tricky for mold fast. The underbelly of raised up wood houses can also be vulnerable to condensation.

If this system holds up the way it says it does, it will be a very interesting option.

I am really rooting for this company, as I think it looks really cool.

Although I’m reluctant to be a test person for something we don’t know enough about I was happy to see Matt Risinger tour this style of home (a company called Holzpur. With the green light from both Matt and SIGA (who sponsored the video), it would make me want to proceed with the next steps of review.

Geographical Area

Most of their buildings are in Europe and you could go see some of the buildings there, including a hotel in Austria, a hotel in Belgium, and a rental. That would be crucial as well, to see how this is holding up in real life. And you can sleep there to see how you feel.

They are also available in the US and Canada.

Cost

The small little room that is just under 100 sq ft is 35,000 CAD.

A tiny house is 39,000 Euros. They make houses of all sizes, including apartment complexes and hotels.

6. GO Logic GO Home

https://www.instagram.com/p/B4fr_hAg4Xt/

These are Passive House-level panelized prefabricated homes. This is another highly respected company. They are a design-build company in Maine. Outside of Maine, they assemble the shell only. Your local contractor does the rest.

Materials and Design

2×8 wood stud wall. Dense-pack cellulose insulation in the stud cavities. Rigid mineral wool insulation between the sheathing and siding.

Taped Huber Zip OSB air barrier. See my post on pressed wood products to review the offgassing of these materials.

The roof is made with prefabricated wood trusses with blown-in cellulose insulation. See my post on insulation.

You can choose from many different design options. Windows are aluminum/PVC or aluminum/wood (triple glaze).

Flooring is concrete and real wood, Marmoleum or tile.

They use high quality finishes like solid wood stair treads and solid wood trim. Interior walls are gypsum with 0 VOC paint. IKEA cabinets.

You can upgrade or change most of these interior finishes.

Moisture Management

They use meticulous air-sealing between the attic and living spaces and ventilation beneath the sheathing to eliminate the risk of moisture buildup and ensure a durable roof.

They seal the critical joints at window openings, between the foundation and exterior walls, and between the wall and roof structures.

Wall assembly is designed to avoid moisture build-up.

They use mechanical ventilation – HRV. Electric heat (like most Passive Houses).

On-site blower-door testing meets or exceeds Passive House standards.

Costs. Size is 600-2500 sq ft from $179,000 to $567,000.

How long have they been in business? Go Logic (founded 2008) company launched the GO home prefabs in 2017.

Geographical area. Delivered and assembled in Maine. Outside of Maine, they deliver the shell only in New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, New York, New Jersey, or eastern Pennsylvania. Your local contractor would provide the site work, exterior, and interior finishes.

7. BrightBuilt Homes

https://www.instagram.com/p/B6gHgsPA8L5/

BrightBuillt appears at first to be a competitor of Ecocor and GoLogic. They make net-zero ready homes that are a bit better than code. Less expensive than EcoCor and GoLogic.

The house arrives in modules as opposed to panels.

Materials

Double-stud walls insulated with dense-pack cellulose. It looks like fiberglass in the roof in some pictures. Some have rigid insulation on the exterior.

Moisture-Management

Air sealing, some use Zip system, some use Blue Skin or Typar. Drainage plane below siding, mechanical ventilation. They have pictures of blower door tests, but it’s not clear if they test all of them.

The lack of information on materials, cross-sections of the walls and ceiling, and details on building science on the website is a red flag for me.

Will they allow prospective customers to tour their factory? Yes.

Customer feedback

They try to be accommodating, but a customer was not happy with their attention to detail or efficiency. Their own photos online show modules arriving with damage to the house wrap and exterior foam.

They claim low VOC, but if they don’t have good enough oversight of their module producer, building for a sensitive client might not go according to plan. You can totally customize the finishes, though.

When a design problem cropped up during the building process, there was no go-to person to address it, a BuiltBright customer claimed. The customer was stuck between the designer and builder, with no one to advocate for them.

If there isn’t a designated project manager or contact person to oversee the project, like what this customer claims, you won’t have the efficiency of what you might expect in a prefab process.

If the management changes in the future this could change.

Process

You have three primary routes you may choose: a pre-designed BrightBuilt Home (from 9 models), a modified BrightBuilt Home, or a custom home.

If you are happy with one of the standard designs, you will simplify the pricing. If you would like to make some modifications to the existing designs, you can make changes to the finishes, spaces/interior design. Or do a totally custom design.

They help you identify a builder.

BrightBuilt designs the modules, passes it on to a company that makes the modules—if anything goes wrong there, BrightBuilt may not be responsible, reports a client. The builder may have to pick up the mistakes made by the other two.

Factory. Subcontracts the manufacturing of their panels/modules out.

Established. They have been in business since 2013. Their parent company (architectural firm) has been around since 2004.

Geographical area. At this time, they construct, deliver, and complete within Maine and the Mid Atlantic region.

8. Module Homes

https://www.instagram.com/p/B601GTCBh7p/

Module uses both wood-based panelized and modular construction. Their houses are built off-site at the Bensonwood Tektoniks factory.

Their first home, the Latham house pictured above, was built to Passive House standards. In the future, all of the homes will be built to the Zero Energy Ready Home standards.

Geographical area. Based in Pittsburgh, modules are made in New Hampshire, they deliver to any area of the US. 

This is a design-build firm: they manage everything “from the first shovel to the last coat of paint”, they claim. Though it’s not clear in which area they provide the full service. The company did not respond by email yet to the question.

Materials

Zip panels with cellulose insulation.

The base model option has fairly standard materials (like IKEA cabinets and laminate countertops). The upgraded options have healthier materials like custom cabinets and solid surface countertops.

Factory. Just like with Bensonwood and Unity, you can tour this factory.

Tektoniks factory is owned and operated by Bensonwood; it’s not owned by Module.

The companies design the panels and send the design specs there to be made. On the Tektoniks site, you can see more info.

Cost. One of their two-bedroom homes is $250,000. An estimated 50K more for site work, foundation, and permits.

How long have they been in business? Since 2017.

You can see a video of their first house here:

9. Haus.me

https://www.instagram.com/p/B18aFNzFNUo/

I’m waiting for a prefab like this to really work for those sensitive to mold and not be too high in offgassing. Something like this has the potential to be very waterproof, with nowhere for moisture to condensate in solid plastic walls.

This prefab is modular; it arrives totally complete. It has a metal frame and then they show a spray foam “composite” that makes up the insulation and the exterior. It’s not clear what that is.

They claim it’s a 3-D printed composite polymer (which means some type of plastic). They don’t say what polymer this is. At first glance, it looked like fiberglass. On closer inspection, it does not look at all like fiberglass. They claim it is VOC-free.

The windows are 6 layers of tempered glass!

It’s mobile—not on wheels, but it can be moved anywhere.

You can schedule a visit to one of their demo units at this link.

Geographical area. They deliver from the facility which is in Reno, Nevada. It takes 2-3 weeks within the US to deliver a house. But they are currently backlogged 9 months.

It is possible to ship an assembled haus.me to any international seaport, which also makes this an interesting option for those relocating to Latin America/the Caribbean.

Warranty

For House Frame and Windows: Five year warranty or lifetime warranty.

Maintenance and Warranty Plan: One year of base warranty and free maintenance for home appliances and décor, including furniture and equipment or ten years of extended warranty and free maintenance.

Year Established. They have been in business since 2016 and this is the first prototype.

Keep your eye on them. When something like this passes the test of time, I will share it on my Facebook page and in my email list.

10. Log Cabin Kits

https://www.instagram.com/p/BxgFZ5Ljb9H/

Although log cabins don’t have a lot of insulative value, and they don’t completely skip past the need for intricate detailing, I like the simplicity of solid wood walls with nowhere for moisture to accumulate and hide (in theory).

The logs need to be debarked and stored properly in good mold-free conditions before the build.

And, as always, pay special attention to the roof and foundation which are done wrong in almost all assemblies, whether it’s in the design or execution. Most foundations have water damage.

They are prone to moisture damage in cold climates. Around windows, doors and building corners are vulnerable areas. Thermal mass improves the performance a bit, but air leakage more than counters any benefit. Cool surfaces + a source of moisture = mold.

I don’t know which log cabin company is the best, but I would use the same criteria of evaluation as with more conventional prefab houses outlined in the beginning of the article.

You still want to have this evaluated by a building science expert to see how log walls will perform in your climate and hold up to moisture and mold.

You also want to evaluate the companies based on their specific “log” system. As these walls are usually square or rectangular, not the classic real round logs.

I pictured Confederation Log Homes because they have a long record and have been in business for a long time. They look like they are building good quality homes, from what I can see in their photos. They passed the initial screening.

11. Method Homes

https://www.instagram.com/p/B5qe0Y3AJUf/

Method makes modular homes that can reach Passive House standards.

Method will build anything an architect designs, as long as it can still be shipped.

Process. You can use their design-build company, Method Contracting, or go with a local builder or general contractor of your choice (“under our direction,” they say). Method has an internal team of specialists and they have an external network of contractors throughout the Pacific Northwest (the US and Canada) that they can recommend and work with.

They don’t say quite as much on the website about building science as the others, but they do say they avoid thermal bridging through either double-stud walls, rigid foam wrap, or a combination of the two.

They do blower door tests to measure airtightness. In order to achieve a very tight envelope, they use the specialty (high performance) tapes like those used to seal the seams of the plywood during framing.

They also use ‘flash and batt’ which is a very tricky method to get right, explained here. I don’t use spray foam in walls due to off-gassing concerns as well as technical difficulties.

They use ERVs or HRVs for ventilation.

This has been reported to be highly customizable.

Materials. Real hardwood floors, 0 or low VOC paints and glues. In a message, a company rep said, “While we use no VOC products, we are not fully set up to build homes for the environmental sensitive community”.

Area served. Method has experience delivering and building in challenging and remote sites, including the San Juan Islands and British Columbia Islands.

Their manufacturing facility is located in Ferndale, Washington. They service the western US and Canada including Washington, Oregon, California, Alaska, Idaho, Montana, Wyoming, Nevada, Colorado, Utah, Hawaii, British Columbia, and Alberta.

Cost. Base price $162,000.

12. Artisans Group

https://www.instagram.com/p/BeFD8D9AjHr/

Artisans Group is a design-build firm in the Pacific North West. They build prefabricated panelized homes to Passive House standards. They can do custom designs or you can choose from their pre-designed plans. I had to email them to clarify: any in their current portfolio is a predesigned plan.

They work with their network of selected prefabricated Passive House builders who deliver the floor, wall, and roof assembly systems to your site.

They use the design-build model because communication between the design team and the construction team is extremely important in order to get things done right.

The assembly is overseen by a Passive House expert.  

Year Established. They are a large firm, in business for 20 years. They claim they have designed more homes to the Passive House Standard than any other US firm. (Ecocor makes the same claim).

They have a good team that is highly educated on building Passive Houses.

Materials. They have been using low and no VOC finishes since the days you had to special order them. (Another good sign they know materials well).

There is not a lot of detailed information on the website about the wall assembly and design. Like all Passive Houses, they do use HRVS (air exchange). I would make sure you can find out more before committing.

You can tour their houses during their yearly tours.

13. Phoenix Haus

https://www.instagram.com/p/BpPi1p9g3hV/

Phoenix Haus is a panelized system that is Passive House certified.

Design & Materials

The Phoenix Haus Alpha System is lightweight timber frame construction, insulated with cellulose, mineral wool and wood fiberboard. The system uses solid timber supports with timber I-beams in the roof. With a ventilated rain screen on the exterior.

An airtight membrane (Intello Plus) is used on the inside of the supporting joists (behind the service cavity). Tescon Vana tape is used on joints. The exterior water-resistive barrier is Solitex.

These are all low offgassing (or practically 0), very common Passive House materials. Most passive houses use these same membranes and tapes.

They do show the cross-section of the designs, which is important information to have.

Geographical area. They can work anywhere from the Midwest to the Rocky Mountains and Pacific Northwest.

Process

Phoenix Haus does the architectural drawings, makes the panels (the panels come with windows and doors), and they deliver them to the site.

The company assembles it and helps you find a builder from their network. You can also choose your own builder.

The general contractor does finishing work (mechanical, electrical, plumbing, flooring, drywall, etc.).

They are open to working with your architect.

Year established. Phoenix Haus has been in business since 2011.

Cost. A 1,500 sq ft cabin costs about $150,000, which usually totals $375,000 with finishes, excluding land and design fees.

They have no pictures of completed houses on their website or Instagram, which seems very unusual to me.

14. BONE Structure

https://www.instagram.com/p/B7WYat5B3Mz/

This is a Canadian company that can ship the components to the US. This is a non-wood based design that uses metal framing and spray foam. My post on insulation talks about spray foam, which I tend to avoid.

Materials and Design

They use both spray foam and rigid foam. They say they have reduced thermal bridging.

They don’t quite make Passive House airtightness standards, which seems strange to me for a house that uses foam as the only insulation product.

Process

BONE Structure will collaborate with 3rd party architects. They will go over their design with your architect.

The company will provide a project manager and can introduce you to builders, or you can find your own builder.

Time to build. On average, the envelope of a BONE Structure home of 3,000 sq ft is assembled in less than 10 days, they say.

I would have this design carefully analyzed by a building science expert before proceeding.

15. EcoCraft

https://www.instagram.com/p/Bf8joQzHvYW/

EcoCraft uses prefab building techniques, but the houses are all custom designed. They build in modules, as opposed to panels. They can be Passive House certified.

Process. They work with local architecture firms. This sounds like they don’t have an in-house architectural team.

They take care of all the building (and the cost includes this): basic excavation, an unfinished basement, walls, roof, finishes, plumbing, electrical, appliances, delivery, installation, and all finishes if you are in the Pittsburgh area.

Materials and Design. They use continuous exterior insulation (rigid foam). Like all Passive House homes, they are built airtight, with a heat recovery ventilator.

They use un-faced formaldehyde-free fiberglass batts within the walls and floors, and blown fiberglass in the attics, along with spray foam insulation to seal air leaks. (You will want to see how much spray foam is used and what kind.)

Fiberglass is a step down from Rockwool/mineral wool.

They use thermal imaging and blower door testing to test for air leakage (which leads to vapor movement).

On the interior, they use low or no-VOC paints and low or no-VOC adhesives and sealants.

Factory. You can tour the factory. You can even be there while your home is being constructed and take photos. The modules are manufactured in a factory located about 90 miles out of Pittsburgh.

Geographical area. They are based in Pittsburgh and build within a 60-mile radius of Pittsburgh. Sometimes, they build outside that radius, or you can use the panels outside of the radius, but they will not be able to complete the build.

Warranty. They carry a 10-year structural warranty and 1-year cosmetic warranty.

Cost. EcoCraft Homes start at $285,000.

16. Bamboo Living

https://www.instagram.com/p/BudE2i5HH_D/

This Hawaii-based company makes panelized bamboo homes. They have insulated walls and uninsulated wall options.

When going with a traditional indigenous building technique, keep it close to the original way of building. Bring in current experts in building science to analyze it, as well. That means no insulation for me with bamboo.

Bamboo is a traditional building material in a huge part of the world. This leads me to believe there is a way to build this in a mold preventative way.

But, bamboo being bamboo (quite the finicky material with moisture), probably means there are a thousand ways to mess this up. That means more research is needed here than usual.

I personally would not ship bamboo panels very far from where they are built.

Warranty. They give a 20-year structural warranty.

Tour: You can tour their homes. You must check out other bamboo buildings first, including a hotel made by this company, and, when they have listings, you can check out this condo made by them too.

Year Established. They have built 400 homes they say. The company started in 1995.

Cost. Base price of $89,000

17. Plant Prefab Living Homes 

https://www.instagram.com/p/BqptxXmll1F/

LivingHomes is Plant’s in-house design studio. I’m mentioning this company because it’s usually on non-toxic prefab lists, not because I’m particularly impressed.

Materials

The construction is standard. From what I can see, they use OSB, Knauf Ecobatt fiberglass insulation, and regular drywall. They use exterior rigid foam insulation, house wrap, furring strips, and Jamies Hardie siding.

They use Anderson Windows (you can upgrade to aluminum windows). Doors are by Thermatru, flooring Millstead Cork Floors (I’m not a fan of cork floors, explained here), kitchen/bath cabinets by Merillat Cabinets.

They claim to be low VOC by using 0 VOC paints and stains, millwork and engineered wood without (added, I’m assuming) formaldehyde, no wood-burning fireplaces. Vents in the bathroom—every house should have a vent in the bathroom, so this should not be their main claim to fame on mold prevention!

These materials are all very standard and any builder can build with these.

They say they include indoor plants to absorb “dangerous compounds”. This is a big red flag for me for greenwashing and lack of knowledge about VOCs, as these plants do almost nothing.

Process

They can work with your architect to create a custom design, or you can choose from one of their standard designs.

You can find your own contractor or they can help you find one.

They coordinate with the general contractor in charge of site work and foundation; they resolve any design issues and maintain oversight and quality-control during the construction process. This is good: if they have this much control over the process, assuming they know what they are doing, oversight is good. A clean line of responsibility between parties is good.

Factory. All Plant Prefabs are built in their factory in Rialto, California. You can visit the factory and see your home being built. (I like this part.)

Warranty. In addition to the standard warranty required by code, they provide a ten-year structural warranty and offer double warranty protection from 2-10 that ensures your warranty will always be covered.

Geographical area. The area they serve is the West Coast of the US and “select places elsewhere”.

Cost. $438,520.00 is the estimated total price for the C6 which has 3 bedrooms and is 1288 sq ft.

So, Which Ones are My Favorite?

Top picks for a regular, conventional house are Bensonwood and Ecocor.

Top pick for something simpler, less conventional are the log cabin kits.

I have my eye on Holz and Haus.me as potentially simple elegant and unique solutions to the safe housing crisis.

Join the mailing list and Facebook page where I will share updates on the companies—which ones have worked out well for folks and stood the test of time.

Thank you!

You have successfully joined our subscriber list.

Those that Didn’t Make the List

Reasons why these didn’t make the list: Insufficient focus on building science. Evidence of poor building practices or lack of anything to demostrate “above and beyond” mold prevention.

Don’t repeat the past with poorly made manufactured homes

Flex house | Delivered complete. The house is made with FSC certified lumber, low or no VOC materials and low Global Warming Potential. BaySeal closed-cell insulation. I’m not a fan of spray foam.

IdeaBox | These are modular homes that don’t look different than mobile homes or your average tiny home. The photos of the build appear to show standard construction with saggy fiberglass insulation. (Not good if it’s saggy).

Greenfab | Some info of green building, but insufficient evidence on advanced building science and mold preventative building.

Blu Homes | Make nods to green building and mold reduction by using wood floors and by “building well” with no actual evidence of how they build differently; how they build well; what their walls, roof, floor systems are; and how they are mold preventative. They do use metal framing, which is especially tricky to manage condensation and thermal bridging in.

Clayton homes | From what I can see from the video, it looks like an exterior vapor barrier, there is no rain screen, and the roof looks like it also has a plastic barrier. These look like typical mobile/manufactured homes.

Dvele | A new company, it sounds like they have display homes as of 2018 in California. They founded in 2016 after running a Canadian prefab company. They are Passive House certified. Use Roxul on all 6 sides, they say. They use some high VOC materials inside like epoxy. You can tour the factory. They use moisture monitors in the walls. Insufficient information on the website to make a call on this. This company might be decent, but if they are building to high standards, they should make this more obvious.

Deltec | Looks really standard. They make wall panels. Tyvek, plywood, regular framing. Not sure how those panels come together, still have to finish the rest of the insulation and everything as usual. They have pictures of what looks like vented crawl spaces (that’s a no from me), and gutters coming off the side close to the house with no kick out (that’s a no for me). I don’t have a lot of confidence in these panels, or the installation, from what I have seen.

MADI Homes | This flat pack house is beautiful and temptingly simple. But from what I could pull out of them in emails and from photos, it sounds like flash and batt insulation plus a poly interior vapor barrier (that’s a double vapor barrier). A no-no for mold prevention in my books.

IT House | I liked the IT House initially, because of the large amount of glass used, and elevated off the ground designs. The structure is metal beams. The panels which are not load-bearing are made of cement board 3form resin panels, and solid wood thin paneling (I don’t really know what that means).

Finish panels are either fiberboard cement or 3Form eco-resin (for interior wet location). I’m still confused on how they build and what the panels look like. Reportedly, they have changed the system since then. That’s why I don’t like protocols. They have not bothered to update the website.

Their display house is a bnb. A friend checked out the display house and wasn’t totally satisfied with the construction. The website says IT House is $150/sf but a client found it to be more like $400/sf in actuality.

The company has not updated the webpage or Instagram for a very long time. A reader reported that they are still very much in business and are busy and backed up.


Concluding Thoughts

Look at the story of Greenterra homes, a company on many green prefab lists just a couple years ago—the company went down epically.

My private notes on this company said “don’t see anything green about them—external foam on metal frame, with poly on the interior, double vapor barrier (no). Laminate flooring with OSB.”

They were clearly building cheaply. It turned out to be even worse than that.

Do not rush into a prefab purchase. As tempting as it can be with all the beautiful and affordable models, and the urgency of safe housing, you have to build this right.

Prefabs are not necessarily better or worse than custom houses. They can easily be worse than most, while many are better than what the average builder can produce. A really good prefab design has benefits, mainly being built out of the rain and with fewer mistakes.

If you need to build something less expensive and smaller see my post on small prefabs.

Contact me for the first steps – looking over which models you are considering, or, to work with a company you chose to make sure you get materials that will be good for your health.

healthy home build consult

Corinne Segura is a Building Biologist with 6 years of experience helping others create healthy homes.

Buy Me a Coffee at ko-fi.com

This post took 30+ hours to research and write and is not sponsored or affiliated with any companies.

If you found this post helpful, you can buy me a coffee to support the research behind this blog. Thank you!


Thank you to Bethany from Building Literate who contributed as a researcher to the post.

Filed Under: Healthy Building, Mold-Free Building Tagged With: Healthy building, mold free building, tiny homes

Designed for Mold-Prevention – Corbett’s Tiny House

January 15, 2020 by Corinne 2 Comments

building a high performance mold preventative tiny house

This post contains affiliate links. Upon purchase, I earn a small commission at no extra cost to you.

Intro

Corbett and Grace Lunsford’s tiny house on wheels (THOW), called the Tinylab, was made as an educational house to teach folks about home performance.

In this article, I’m going to outline the areas of this tiny house’s home performance that are relevant to mold prevention.

These mold preventative aspects of the house are:

  • Air sealing to prevent vapor from entering the cavities of the enclosure.
  • Using vapor retarders wisely, to prevent condensation in walls and the roof.
  • Insulation installed without significant air leakage (air leakage = vapor movement = condensation potential).
  • Windows flashed and taped correctly to prevent water infiltration.
  • Using ventilation to reduce humidity, and avoid negative or positive pressure which can push or pull air through the walls and cause consequences.

I also outline some other facets of the house that make it a healthy home. These are:

  • Low VOC materials
  • Improving indoor air quality by reducing carbon dioxide, carbon monoxide and VOCs
  • Controlling humidity
  • Managing microbial growth in tanks
  • Energy/Power system which provides for flexibility of location

I haven’t seen many tiny homes on wheels built really well. This is only the second one after Terran’s house that I have featured as a mold preventative build.

Air Sealing is Key

In Corbett’s High Performance house, air sealing is incredibly important. Air sealing is how you prevent air from entering the wall and other cavities. This is important because air carries vapor, and it’s usually at a different temperature.

Air leakage brings with it vapor that can condense on hidden surfaces.

This build used materials that are made for Passive House design. Passive House is a design process that includes a major focus on controlling for moisture and condensation within the walls, ceiling, and foundation.

The Exterior Water Resistant Barrier (WRB)

Solitex Mento membrane and tapes were used, just like in this detailed example.

Solitex Mento is a breathable house wrap/WRB that comes with a line of high-quality tapes for sealing around all seams and openings.

Most houses should have a breathable exterior water-resistant barrier over the sheathing, with a vented rainscreen system. A rainscreen is battens that create a gap behind the siding. This lets moisture escape and dry out.

These products are good at air sealing and they are also lower VOC than liquid applied barriers. Many high-quality builders are now using liquid applied barriers in many areas of the house, and that might not work for all chemically sensitive folks.

Interior Vapor Retarder

Inside, the Intello brand smart vapor retarder was used to prevent moisture from entering the cavity in the winter and let it breathe more in the summer, preventing condensation within the wall cavity.

We want to get away from using vapor barriers that trap moisture. Instead, these two permeable membranes, one on the outside of the wall and one on the inside, control air flow, and slow vapor flow but don’t stop it completely.

The Insulation

With Rockwool R 15 in walls and ceiling, the Tinylab house can be moved around the US to multiple climates. You always want to design the house with one climate in mind to optimize all the systems (and the whole house as one system).

This house was built for Atlanta. As they moved the country they had the most difficulty with humidity and condensation in very humid and very cold climates. They attempted to follow the weather to reduce this challenge before returning to Atlanta.

Rockwool is easier to pressure fit into cavities compared to cotton batt. They tried the recycled blue jean insulation at first, but it was sagging in the ceiling, and leaving a little bit of air gap in the wall cavities. You can see that here.

Rockwool holds itself in well with a friction fit in both the ceiling and the walls, without sagging and leaving air gaps. The tighter it is to the framing the better.

If your insulation is not tight to the framing air leakage can lead to moist air moving through the wall and condensating. A lot more moisture moves into the wall with air leakage than with diffusion. Diffusion itself moves very little moisture, not enough to cause problems in a well-designed wall. Matt Risinger explains that in this video.

You need to take your time to cut and fit the insulation as perfectly as possible so that you don’t have air leakage.

They didn’t use spray foam, even though folks like the idea of insulation that in theory is an air sealant and a high R-value insulation product in one.

In reality, spray foam often pulls away from the walls, in which case you lose the air seal. And in a tiny house on wheels that is moved around, it’s going to crack and come apart from the studs almost for sure. Bad idea.

Here is the interior air barrier and air sealing:

Low-VOC Materials

There was a big focus on 0 and low-VOC materials throughout the whole build which I appreciate seeing, even though the Lunsford family is not chemically sensitive.

Walls and Cabinets

Purebond plywood which is made with a “soy glue” (probably a polyurethane glue) was used for the interior walls and cabinets as well as the interior door.

If you are sensitive you should test this out for yourself. I prefer plywood made with phenol-formaldehyde which has a defined short period of offgassing before it cures, compared to an unknown glue and VOC that we know less about.

For the walls here I would have preferred just a solid tongue and groove wood. With plywood only used for cabinets.

Flooring

The floor is APC Cork, which looks awesome and is great for sound dampening. For most moderately to severe chemically sensitive folks, cork flooring is too high in polyurethane glue (and VOCs).

There are many similar floors you could put down in a tiny house that are extremely low (lower than this) in offgassing. I list them here in my flooring post.

Insulation

Both Rockwool and EPS (polystyrene) foam insulation are used in the house. Both healthy choices. Rockwool is my go-to insulation to consider before moving on to more unusual options.

My insulation post goes more in-depth into insulation choices and why rigid foam is still a good choice for most sensitive folks.

Rigid foams are frequently used as exterior insulation (outside of the framing) as part of the system design to prevent thermal bridging and to help prevent condensation.

This video has some good information on the insulation:

The Devil is in the Details (Like Window Flashing)

When designing and building a mold preventative house, the devil is always in the details. Flashing is an area that is more often than not done wrong on new builds (along with the air sealing layers like the house wrap).

I liked this detailed video below on how to properly install a new window to prevent future moisture issues.

Maybe this looks simple and like anyone who can follow instructions can do it, yet almost every builder makes mistakes here.

It’s rare that I see a build in progress with the house wrap/WRB and all flashing done right. You should supervise this part of any build.

When windows and other openings in the exterior are not detailed right, water that gets behind the siding finds its way to the plywood or OSB sheathing. Enough moisture will cause water damage and mold here. As damage continues it will get into the framing and wall.

In regular builds, other openings in the wall for vents or wiring are often left without any sealing (flashing)! Big problem for water and air getting in.

Water is expected to sometimes get behind the siding – that’s not a fatal situation. It’s supposed to be able to drain, dry to the top and bottom, and stay out of the walls.

The windows are Pella brand wood windows with aluminum cladding on the exterior. The caulking recommended for this combination of materials is DAP 3.0 Window, Door, Trim & Siding High Performance Sealant.

Here are the WRB instructions from 475 if you prefer diagrams to video. All the brands come with detailed instructions, there is no excuse for a builder to not know how to do this.

Exhaust and Ventilation

What Happens if you only have Exhaust Fans

The object in the Tinylab is to have active balanced and controlled ventilation.

It’s easy in a tiny house to create negative pressure with a high CFM (CFM is the amount of air it’s moving) bath fan or range hood. This pulls way too much air out for such a small space. This can happen in any well-built air-sealed house, but it’s exaggerated in a small space.

The problem with that is that you start to pull in air back through any gap that the air can find a path through. And back through places you don’t want to pull through – like exhaust vents or even the composting toilet in this case! You might also be pulling in moist outside air.

You aren’t getting healthy make-up air this way (which is the air that’s coming in to make up for that exhausted air).

Why you want Air Moving In and Out

Without enough air exchange (air coming in and going out) in a small space, you can also raise your carbon dioxide.

Having air exchange (meaning you replace the indoor air with fresh outside air in a controlled way) is the best way to reduce carbon dioxide, VOCs and other pollutants, like those produced by a gas stove.

This house has a number of high tech ways to manage the air quality and replace the air.

An Energy Recovery Ventilator

A Broan HRV (later switched out to an ERV) exchanges indoor and outdoor air in a balanced manner. The ERV is working better for them in their climate because it buffers both humidity and temperature.

You need to look at the house as a system and your climate to determine which one you need.

The negative air (exhaust) side of the ERV is venting out of the bathroom, and the positive air (incoming air) is coming in over and under the loft.

The fresh air comes into the loft area with a damper to control whether it goes down to the sleeping area below.

This video explains what an ERV and HRV do and what the difference is.

Exhausts and Make-up Air

The composting toilet and kitty litter box area has a 3 CFM exhaust vent to keep that air moving out (a very small fan, just enough to keep it moving out).

The gas stove has an exhaust fan venting out over it, to pull out moisture, carbon monoxide and other pollutants and particulates from cooking. When this fan kicks on, it opens up a damper that brings in fresh air right under the stove. This keeps air circulating and moving out right where you want it to.

You can see it in action here:

Monitoring the House

The house has a number of cool monitors that help you know that everything is functioning as it should be.

Carbon Monoxide

Defender brand low-level Carbon Monoxide monitors detect low levels of carbon monoxide. This is important if you are running appliances on fuel. Your carbon monoxide level should be 0 in a healthy home.

Elderly, children and those with compromised health are more affected by low levels of carbon monoxide. The cheap monitors are only going to show you when the level is already too high.

Radon

Corbett has a radon monitor from Trutech tools, which is useful in a regular house. Though here it is used for teaching purposes. If you are not on a foundation you don’t need a radon monitor. (Though if you have a granite countertop this might be interesting to see!)

Corbett is aiming for 0 radon in all his houses.

C02 & VOCs

The Foobot monitor tests for carbon dioxide (what you breathe out, this will show you if you have enough fresh air), VOCs, particulates, temperature, and humidity.

Pressure

Retrotec manometer measures the pressure inside, making sure it’s where you want it to be. In the Tinylab they are making sure it’s more or less equalized.

It also monitors the pressure of the incoming air through the ERV. Just an extra data point to show Corbett that everything is functioning, and for educational purposes. For most people, this extra step would not be needed.

Though it would be interesting to see the pressure in the house as a whole. Just seeing that would tell you if something is wrong with one of your fans or exhausts.

Temperature

Two Dwyer temperature gauges measure the temperature of the incoming air through the ERV, and the air inside the wall on the backside of the insulation. These show how well the house is managing the temperature.

The temperature gauge on the inside of the sheathing can help you to calculate if there is a risk of condensation on the sheathing or exterior vapor barrier (if you have an exterior vapor barrier). Especially if that is coupled with air leakage (which you can use an infrared camera to check for).

A third gauge wraps around a plumbing pipe under the stove to see if there is a chance that pipe will freeze. Smart!

Mechanicals / Systems

Greywater & Blackwater

The greywater tank is on the exterior and is portable and on wheels. I like this idea as you don’t have and scum build-up inside hidden tanks. And not having a blackwater tank definitely cuts down on the kinds of bacteria and mold you might be fermenting in your tanks. (They use a composting Air Head toilet instead).

Freshwater

The freshwater tank, stored inside under the sink, won’t freeze. It uses chlorine to keep it bacteria and fungi-free, it’s not for drinking unless you want to filter the chlorine out.

In the last section, you can see the major leak they had with this tank and how they put more precautions in place after that.

Fuel & Electrical Systems

They have three solar panels that are portable, on a long cord and are set up on the ground. They can be moved around to maximize sun exposure. It’s not a great idea to put panels on the roof; more holes = more chance of leaks there.

You can also plug the house in; the whole house runs on one extension cord that runs off a regular house outlet (15 amps). That is an impressive (low) amount of power usage. It gives you the ability to be super flexible with where you live. Either going off of solar and propane, or one plug into any house.

The stove and hot water heater run on propane, which cuts down on electrical usage.

The Mitsubishi mini-split only needs to produce 5000 BTU of heat, 4000 BTU of cooling to keep this house warm and cool enough for their climate. It runs off only 200-300 watts.

This is something you need to calculate in at the design stage. You don’t want an oversized or undersized system.

Mini Split heat pumps are ductless systems, they do not bring air in or out of the house.

This does a little bit of dehumidifying, and in some conditions, the ERV helps too. But they also found they had to add this desiccant dehumidifier.

This video shows the mechanical systems and is a good overall tour:

Design of Walls, Ceiling, and Floor

Floor Design

The base of the house was designed to use the trailer cavity as an insulation cavity. EPS foam with foil backing was placed in between the metal trailer joists.

Underneath the whole trailer, there is a metal barrier to prevent water from splashing up. There is no thermal break underneath the metal trailer framing. This is a typical design for tiny homes on wheels.

On top of the framing, plywood is placed against the metal. It looks like there might be a slight gap between the EPS and the wood.

I wouldn’t recommend this design of the floor system in terms of preventing condensation and mold.

In fact, the flooring system is where you should put the most thought and planning. Bring in an architect like Cheryl Ceicko, or Passive House designer like Mike Maines.

It’s easy and common to have condensation in the flooring of a tiny house on wheels. The metal trailers make this difficult. There is a lot of thermal bridging. You need to decide between thermally breaking this underneath with foam or building up a breathable system on top.

Those who have designed with mold prevention as the main goal have all built up on top of the trailer. This post shows a detailed example.

EPS is also used around the metal wheel wells, a place that is prone to condensation.

Roof/Ceiling

The roof has plywood decking with foam exterior insulation on top (1 inch EPS), then Solitex Mento, then a rainscreen, then 26 gauge metal roofing.

Walls

The walls are regular 2 x 4 framing with Rockwool, plywood sheathing, a rainscreen, and is breathable to both sides with the Solitex and Intello products.

Make sure your rainscreen is vented, it’s a tricky detail in tiny houses on wheels.

What went Wrong?

A Flood

The Freshwater bladder did leak and it was quite the flood. After that, the Lunsfords put some precautionary measures in place.

Anyone preventing mold would want to do this from the start, making sure a leak-prone area is a waterproof protected area and you have these leak alarms.

Mattress on the Floor!

The foam mattress was put right on the floor. Always a no-no! This causes mold underneath. They changed over to an air mattress which does not let moisture transfer through it.

Condensation in Storage

They also had condensation on the wall in the backside (at the back of the drawers that were full of clothes and things) on the really cold days. That’s a place to keep an eye on. You may even want to design your storage a little differently in a cold climate.

Realistic Expectations

Corbett doesn’t have unrealistic expectations on how long a tiny house will last. He says no more than 30 years.

They put a lot of miles on the house but it was designed with an engineer to make sure that it would hold up to those forces. In that sense, it was designed well for the motion.

Building a tiny house when you have sensitivities is in a way a trickier endeavor. You are in a much smaller air space with all the items that offgas that you can’t avoid – appliances, flooring, caulking, glues, windows, doors.

You are also in a much smaller space with EMFs and you cannot get away from that.

In the end, I still like tiny houses for those with mold and chemical sensitivities, but only if you know full well what you are going into and have taken the time to design a detailed mold preventative build.

There’s a lot of work involved here – you are designing a full system. Just about as complicated as a regular-sized house.

The only part that is easier due to the size is that you have an easier time supervising the build. The HVAC is also less complicated.


I am currently taking Corbett’s course in Home Performance to become certified with the BPI as a Building Analyst. Corbett consults on home performance, and you can contact him here.


Corinne Segura is a Building Biologist with 6 years of experience helping others create healthy homes.

healthy home build consult

Did you find this post helpful? If so you can buy me a coffee to support the research and writing behind this blog. Thank you!

Buy Me a Coffee at ko-fi.com

Filed Under: Mold-Free Building, Tiny Homes and Trailers Tagged With: mold free building, tiny homes and trailers

What are the Causes of Mold in Tiny Houses?

November 25, 2019 by Corinne 1 Comment

 

common areas that go moldy in tiny homes


This post contains affiliate links, upon purchase I earn a small commission at no extra cost to you.

1. Built by Non-Experts

Highly skilled builders are rare. They tend to focus on upscale houses because that extra work and time they spend to build something right does translate to more expensive homes.

Most tiny house companies I have seen were started by contractors who don’t have much experience, they certainly don’t have the expertise in building science (which is mold prevention), and high craftsmanship.

Most small companies I have looked at started with someone who had not even managed a whole house build before! That was the case with my builder.

Even if a company is well established, it’s rare that an architect or other building science expert is recruited as a designer and consultant on a tiny house build. It is necessary to have that building science expertise to building anything that will hold up to mold, no matter the size.

My resource page contains links to architects, builders, and building science experts who I think are good.

I certainly wished I had chosen an experienced builder who really cared about details, and hired an architect to design and manage the project.

2. Building Codes not Followed 

Building codes are not perfect, they are only the bare minimum requirements and even though they are just the absolute bare minimum of what needs to be done on a house, they are not usually followed.

To build a truly mold-resistant (regular) building you have to hit many of those codes right on and in many other areas go above and beyond those codes if you want the house to hold up to moisture and mold.

Tiny houses don’t even meet those codes on some of the most basic building standards. If you are having trouble finding a regular house that does not have mold, I don’t have good news, tiny houses are built even more poorly.

For some areas of the build, RVIA certification could help ensure things are done better. But some RVIA codes are not mold preventative (like the requirement a vapor barrier), that could make things even worse!

Look at RVIA codes and see if that will work with your moisture management system. You may have to forgo that certification. There may be important guidelines to follow there for general quality (plumbing, electrical, fire safety), but not necessarily for mold prevention.

You can build a mold preventative build (like this one) and also meet the International Residential Code (IRC) (which would be a good idea).

 3. The Trailer is Tricky to Insulate

All Tiny Homes on Wheels are built on a metal trailer – that’s a tricky interface for condensation in most climates. Building the house by using that trailer as a floor cavity is a bad idea.

The house should be built up on top of the trailer, and even then there are many very detailed decisions and details to consider and execute. See this post on a Mold Preventative Tiny House for details on the trailer base.

4. Metals Frames 

Many THOWs are also made with metal framing. That is really tricky too! Now you have a whole house with thermal bridging and the possibility of condensation in the wall. Even if you go with all foam for insulation, this has to be well thought out and designed well.

I have seen trailers with a metal frame and then an organic insulation! No!

The wheel wells, another metal area, are also particularly difficult to insulate and are usually done wrong. The wheel wells in my tiny house went moldy within the first 3 years. They need to be thought out and detailed right.

Hire a building science expert to design your building envelope.

5. Which Climate is it Built for?! 

Tiny homes are often moved throughout many different climates in the US and Canada. Which climate was it designed and built for?

Even if some thought was given to design the building envelope and HVAC for that climate, will it now be moved to many different climate zones? How will the house perform in those?

If the house is made for multiple climates that has to be factored into the design of the entire envelope and moisture management system as well as the HVAC right from the start.

WUFI is one program that you can use to model the moisture in the house and see how it will perform in various climates.

6. Movement is not Your Friend!

Taking a house and then jostling in on the highway does not lead to something very durable. All those little details that need to add up to have things perfectly sealed and flashed do not benefit from a lot of movement.

You can easily lose the integrity of your sealing or flashing here, you may even have trouble with your framing or siding. Problems with your framing could lead to problems with your doors and windows and more…

7. A One Year Warranty??

Many tiny houses are very expensive and only come with a one year warranty! What!

What other 60K item would you buy that only has a one year warranty? Builders can get away with a lot because major mold problems will take longer to show up than one year.

My house had a few problems in the first year, but there were other major problems that took more than a year to show up. Mold above the shower in the ceiling, mold on the framing, an insulation system in the floor that was not done right – I fixed these myself on my own dime.

Ben Garrett (Tiny Healthy Homes) who built my house only paid for things that went wrong in the first year. He then changed the name of his business (and so I could not sue him). That’s another reason these small companies are very risky. I lost 100k as a result of the building defects in that house.

Though I did learn a lot about building science when I took it apart! And this did lead me to become certified as Building Biologist to help others build low offgassing, mold-safe houses.

The most helpful course in mold prevention is Cheryl Ceicko’s Building a Healthy Home.

8. Siding is Prone to Mold

Siding is frequently done wrong on tiny houses. Mold preventative siding almost always has a rainscreen with very few exceptions.

Regular wood-framed houses almost always require a vented rainscreen siding system to prevent water damage and mold. This is rarely done on a tiny house.

Most houses I have seen have siding right up against the sheathing. Sometimes it’s permeable siding, meaning solar vapor drive can drive moisture in, but even if it’s not, it prevents drying from the inside out. And you are losing your layer of protection from water entering behind the siding.

A rainscreen helps water that will get behind your siding drain out.

I highly recommend Cheryl Ciecko’s course on building a mold preventative house which is now evergreen, you can start the course at any time.

To hear about future course you can sign up for my email list:

Thank you!

You have successfully joined our subscriber list.

9. Roofing Prone to Mold 

Regular sized houses have a fairly complex roof system that often has venting. An unvented roof (like tiny house roofs) would have to be done really carefully.

In a small space, your roof cavity can start to mold fast. Mine did over the shower as the builder had no interior vapor barrier and the breathable roof sheathing membrane was enough to trap moisture there.

Many tiny houses also have roofs that are flat or don’t have the right material for the slope.

Here is an example of a highly detailed mold preventative roof.

10. Details not Done Right 

The devil and mold prevention are in the details. Window flashing, house wrap installation, house wrap taping, metal head flashing, the detail below the rainscreen, flashing on any permeations going through the wall, details around the door- all of these are super crucial.

It’s especially important to get right due to the lack of overhangs over windows and doors on most tiny houses. This means everything has to be done perfectly. The overhang on a regular house is insurance against too much rain hitting these vulnerable areas.

healthy home build consult

Filed Under: Mold-Free Building, Tiny Homes and Trailers Tagged With: mold free building, tiny home

Building for the Chemically Sensitive

September 15, 2019 by Corinne Leave a Comment

Those who are building and have moderate to severe chemical sensitivities have a number of factors they need to consider in the very early stages of the planning of the build. You could easily end up between a rock and a hard place without considering these details in advance. I have seen it many times!

It’s incredibly important to build in a mold-preventative manner in order to recover in the new house, and it can at times be difficult to balance those two needs together. So the following areas to consider also apply to those building for mold prevention.

This post contains affiliate links to educational products I use and recommend. Upon purchase, I earn a small commission at no extra cost to you.

Here are areas that must be considered in the very early stages of planning a house if you are chemically sensitive:

“Sv sava topography P.Cikovac” by Orjen is licensed under CC BY-SA 4.0 

LOCATION – BEFORE YOU DRAW UP THE HOUSE 

1. Climate

Before you draw up plans for your house, you need to know the location primarily because you need to know the climate zone. This will impact your design significantly.

This can impact your foundation type (and many who are building mold preventative want to use a specific type of foundation), it will also impact insulation requirements – with many areas in the US starting to require exterior insulation, you need to know if you can tolerate Rockwool Comfortboard, rigid sheathing or cork, for example.

It will impact many other materials choices as well as HVAC system requirements.

If you are deciding between two cities or towns we can still start to put your materials list together and see if that impacts the type of house you can build in each area.

2. Topography

The exact piece of land can impact the design as well, since you will look at the topography of the area and site itself, and how that will impact the design – this could influence the size and shape of the house for example, as well as how the crawl or basement is designed, where you will place the garage etc.

This is also important to factor into your budget. If you have a slope or are creating a hill for the house drainage it will impact costs as well as the lot size (distance you need from other houses/property lines).

Though you could work the other way around, pick land that is flat enough and large enough to fit your design.

3. Building Codes

Another reason you will want to know the location, including possibly the exact location, is because building codes and neighbourhood requirements will impact which materials you can use.

These could be codes around things as major as the minimum size of the building, and as small as the type of plumbing you use, for example. Those with MCS are often on a budget and want to build small, and you will almost certainly have materials that you have to rule out due to sensitivities.

4. Neighbourhood or HOA Requirements

Neighbourhood requirements can impact facets of the build like the type of siding that is required. In some historical areas wood siding is required, sometimes even a specific type of wood. Wood siding is not the most durable option for rot prevention, and those with MCS may need to avoid certain types of wood (like cedar).

There are areas where roof types are dictated by the local requirements, this could rule out a metal roof (which is what most with MCS want to use). There are areas that require flat roofs (though you can make it look flat usually and meet that requirement). Those are just a few examples.

EARLY STAGE DECISIONS- AFTER LOCATION BEFORE DESIGN

1. Wood Framed House?

At this point in the process, you will need to have an idea of what materials you tolerate. The more info you have on which materials you tolerate the better.

Most who are sensitive to wood are not sensitive to wood when it’s in the walls – but you need to know which category you are in. You need to know if you are designing a wood-framed house or something entirely different!

If you are avoiding wood altogether you may want to consider other climate-appropriate options which could be metal and foam, metal SIPS, adobe, hempcrete, concrete, and insulated forms.

I discuss alternative walls systems in this post. The post on tiny homes talks about some other unusual systems.

My post on (regular sized) prefabs covers more alternative systems.

Choosing the materials that are tolerable and healthy for you is one of the main things we will cover in a one on one consult.

2. Plywood and OSB?

While many with MCS want to avoid plywood and OSB, avoiding those two items will create a lot of “work around”. Most sensitive folks do use plywood though not all.

You may be able to use alternative sheathing, or you may have problems with code, you may have a much more expensive house, or you may in the end have to go with a totally different type of house than a wood-framed one.

I encourage those with MCS to read through this post on plywood and OSB before ruling it out.

I help folks go through these areas of the build that they have to consider, test options, and weigh the pros and cons of the alternatives.

There are ways to offgas and even seal plywood which could in the end save a lot of money and worry. Or you might want to build with an alternative wall system.

3. Insulation?

You should also have an idea of which insulation you can tolerate. This is another main area that comes up in every consult.

Your typical build has rigid foam in the slab, breathable insulation batts in the walls and depending on the design and climate, spray foam in the attic.

If you need to avoid spray foam insulation (which in general I would), you need to make sure your design takes that into consideration.

With batting, go through the options in the insulation post, as those are the ones we will go over in a consult. If you cannot tolerate any of the insulation batts, again, this will dramatically change the type of house you build.

“WALLTITE spray foam insulation being applied” by Cdpweb161 is licensed under CC BY-SA 3.0 

DURING THE DESIGN PHASE

Decisions that impact the design

1. Avoiding Spray Foam

If you don’t tolerate spay foam insulation make sure to design a roof and foundation that do not require it.

2. Avoiding Laminated/Engineered Lumber

If you want to avoid laminated/engineered lumber to avoid extra glues (see this article to see what I mean), this has to be considered very early in the design. You can only span so far with traditional lumber, so this will change the whole design of the house.

3. Avoiding Ductwork

If you want to avoid all ducted HVAC due to extreme mold sensitivity, this has to be factored into when designing a house.

If you want to avoid AC altogether due to sensitivities, that part definitely has to be factored into even earlier into the location. Even if you don’t mind hot temperatures, you have to look at summer humidity since AC brings down humidity.

4. Design Areas to Consider

Consider simple roof designs to cut back on where things can go wrong, consider large overhangs to protect the walls, simple floor plans can help with cost reduction, carefully design plumbing in an interior wall that has access panels.

5. Avoiding Toxic Windows

You need to design the house around the windows! Yes this is that important of a factor. Many super chemically sensitive folks have run up against this problem too late in the build.

First, the very sensitive will want to go with aluminum windows (see my post on windows), and those can only be found in certain standard sizes (unless you go for totally custom, very expensive windows).

Aluminum windows are already expensive. If you don’t design around those sizes you are going to end up with either windows that you don’t tolerate potentially (fiberglass, vinyl), reframing the house (big expense), or custom windows (another big expense).

“House Plans: Front” by Fugue is licensed under CC BY-SA 2.0 

AFTER DESIGN BUT BEFORE BUILDING 

1. Testing Materials

In order to not delay the build you want to make sure you have tested out all the materials needed down to the caulking, glues, sealants, grouts, thinset, and all the major materials as well.

What can happen here is that if you need to make a substitution, some items are special order and need to be considered early on.

You don’t want to delay the project with special orders and you also don’t want to delay the project because you need more time to test out materials.

If you are extremely sensitive you will either be factoring time in for the house to offgas before you move in, or possibly building a type of wall system that limits the types of glues, caulks, tapes that you are reactive to (alternative wall systems are listed here).

There are certain corners that cannot be cut while trying to eliminate offgassing. I’ve seen it done a lot in houses built for the extremely chemically sensitive. But long-term, you cannot cut corners on the integrity of your building system which is designed to keep out water, moisture, and air. Preventing mold is very important for those with MCS. Cheryl’s course on building a mold preventative home is essential.

You want a builder who understands when materials can be substituted out and when they can’t. Some builders will do whatever you want done because they don’t have a high degree of understanding of building science, and so they don’t know why that will fail.

Or, on the other hand, they may be too rigid and reluctant to change anything, again because of lack of knowledge of how to keep the integrity of the system while doing something slightly different.

I will work alongside your architect and builder to make sure that the right compromises are made.

2. Contracts

Make sure the builder understands your level of chemical sensitivity and how important this is. You need to have certain requirements here in your contract to protect your site and your build. Paula Baker Laport outlines this in her book Prescriptions for a Healthy House and Cheryl also covers key areas of the contracts in her course Building a Healthy Home.

You also want to work with your architect to produce a contract that will help protect you on the mold-preventative building front.

CHOOSING AN ARCHITECT AND BUILDER

1. Your Architect

An architect is needed in any build to help design the moisture management systems.

An HVAC specialist will likely be needed if you are doing a ducted system (or any other complex system).

When looking for an architect, you need someone whose specialty is mold prevention and/or high-performance systems like Passive House.

Anyone who has a high commitment to design and details that prevent moisture problems, rot, decay, and mold is what you are looking for. This can be worded as fine craftsmanship, high performance, increased durability and similar terms which are geared at the non-sensitive.

These builders do higher-quality work, their houses cost more and they have to market this to the general public as high performance or durability.

This video goes over the conflict between finding a builder who builds high quality mold preventative houses and one who will build for MCS. Many get scared away by clients with MCS as it costs them money and time and so it’s important to have your materials list well thought out before contacting them.

2. Your Builder

The same thing goes with a builder. A builder should be highly skilled, highly detail oriented, a perfectionist with getting the details right, someone who understands building science and has an interest in it. A good problem solver, can think outside of the box to accommodate you, while also understanding any repercussion of going too far against the norm.

The builder should have total buy in to the idea of building to accommodate your sensitivities and be thoughtful and mindful so that the wrong products are not brought in accidentally, in a hurry or to clean something up.

You builder should also be highly cooperative with your architect and with you (or your supervisor).

Highly skilled builders will be interested in building a well planned and very well executed house and will not have a problem with working with your architect and you to get it done right.

If they are not used to building high quality work, this will be a battlefield.

You can find a good builder through a good architect or you can find one on your own who you like. When I see high quality builders I list them here (though I don’t know all of them well, and they are only as good as the weakest labourer or as good as their supervision).

Please get in touch if I can help you through the process, especially to make sure you know which materials are best for you so you can design your house around it. And we will make sure you have the right experts to build a high quality, mold-preventative, low offgassing home.

healthy home build consult

Filed Under: Healthy Building, Mold-Free Building Tagged With: Healthy building, mold free building

Passive House Tiny House – A Detailed Mold Preventative Build

September 4, 2018 by Corinne 11 Comments

Intro from Corinne

What it takes to Build a Mold-Preventative House

This post is about a meticulously built tiny home, designed to hold up in the long run to mold.

The post is written by the owner/builder who did years of research and consulted with many building science experts.

There was an extreme attention to detail on preventing mold.

The main reason almost every house is moldy is because of the many mistakes made in both design and execution.

These mistakes can be even more prevalent in tiny homes – which are less regulated and often built by non-experts.

This post serves as an example of the care, research, consultation, and attention needed to build a tiny house that will hold up to mold. There is no other article like this online nor in books so I’m very grateful to Terran!

The owner/builder, Terran, also has TILT (also known as chemical sensitivity). There is a focus on healthy materials in the build as well as mold prevention.

This post may have ideas you can use in your own build and it is also interesting to see the kind of detail needed to carefully build a house.

The build itself took over a year.

This house uses many practices from Passive House building so there are some unique aspects, but many of these designs can be applied to most tiny houses.

Never simply copy someone else’s building practices without consulting with your own architect or engineer who specializes in mold prevention. If you change the materials due to availability, or your own sensitivities, or you live in a different climate your house will likely be different.

Any ideas here should be reviewed by you and your experts. That is not a legal disclaimer, that is just what needs to be done to build a home that will last. 

This post does not go over every detail of the build, as that would take a whole book. But it does cover the main tricky areas and how they problem solved for mold-prone areas, as well as the main materials used.

Even if you choose just to look at the pictures, this will be interesting to anyone looking to build a safe and healthy tiny house.

Whether you are a beginner who does not know the full complexity of housing systems or a contractor this post has new ideas presented in detail.

I am very excited about this post. I think it adds something really important to the tiny house conversation.

The following is written by Terran and has a few comments inserted by me. It has been edited for grammar and length by me. The owner himself will be away from the internet for 3 years from the date that this was first posted. His personal website is here.

This post is not sponsored by any of the companies mentioned. Some products mentioned have affiliate programs. Upon purchase, I earn a small commission through affiliate links at no extra cost to you.

For individual help finding a skilled builder and selecting healthy materials for you and your building system, you can contact me for a one-on-one consultation.

Enjoy,
Corinne

Intro from Terran the Builder

About three years ago I set out to build a Tiny House to help with chronic health problems I’ve had since childhood.

The structure would need to be free of chilling drafts during colder weather (it gets down to around -30 F), free of building materials that caused Toxicant-Induced Loss of Tolerance (TILT), have a good (and properly sized) supply of fresh air in the form of Heat Recovery Ventilation, and would need to be as efficient as possible.

Early on we struggled to find materials that would fill these needs. We thought it seemed likely that we would wind up building more or less another version of the kinds of structures that have made life challenging for me in the past. But then a retired contractor mentioned Passive Haus/Passive House (PH) to me.

For several months, I’ve been living in the final product of what we built, and it has changed my life. It is by far the most beneficial structure for my health that I’ve ever lived in. Because of that, I really wanted to take the time to explain our build.

I’d be really happy to know that others in the Tiny House community might be able to build on what we’ve done, and improve it. They’re awfully small spaces to share with moldy surfaces and cavities of walls, roofs, and floors that have moisture issues over time. I have heard horror stories of how much these factors can impact Tiny House occupants.

The envelope design we settled on has a number of points where it differs from other Tiny Houses I’ve seen, so I’ll try to explain why and how it differs in this post.

I’ll start with how we went about planning the design.

Part I: Design and Testing

During the early part of the planning phase, the amazing and kind Hans at Pinwheel Structures in Ontario, Canada suggested that I try using U-Wert in order to test moisture and efficiency performance of my wall, roof, and floor assembly ideas. U-Wert (German for “U-Value”) is a program that people can use for free online to perform basic WUFI-style analyses of any given assembly in their building envelope.

There are more advanced features available through subscription.

The English version of the program itself is still partially in German.

There are full listings of analysis information for nearly all brands and styles of Passive House Certified Materials, as well as a wide selection of the other common building materials.

The listings include factors like permeability, u-value, thermal delay, thermal mass, and nearly all the other important statistics for Passive House consideration.

Once putting together a given assembly design, one can set interior and exterior temperature and humidity to see how the assembly performs under different conditions.

Because I figured I only had one shot at getting our design right, I got a little addicted to the program.

At 475’s recommendation, I also bought a copy of the Passive House Planning Package (PHPP). The PHPP was learnable, with some real attention and effort, for a layperson like myself – and the amount of climate-based information it offered was invaluable for understanding what’s required to build a Passive House.

After working with the PHPP for many hours, I was able to get a sense of how much energy I’d be using for the plan I settled on.

What I needed was a design that could be potentially mobile, was specifically designed around environmental health issues, and that fit into an incredibly small budget.

The home will also be empowered by the fact that it can be physically moved (and therefore re-oriented) each season, to give it the best performance for any particular time of year.

After more U-Wert and PHPP test-runs than I could count, we settled on a design that has a few calculated risks, largely for the sake of maximizing foam-free efficiency. I want to be sure to explain those.

Part II: Walls, Roof and Floor

Walls

The first of these risks is that instead of using a continuous layer of exterior insulation, such as Gutex (covered by battens and siding as normally prescribed) we chose to go with Facade-Grade Thermacork.

Facade Thermacork has essentially the same u-value as wood-fiber insulation, but can be left exposed to the elements for a lifetime, and is designed and tested to stand up to almost any kind of natural exposure (except woodpeckers…it doesn’t like woodpeckers! Just put up some mylar balloons when it first goes in, and they’ll stay away).

This function of Thermacork is not a risk, it’s been relatively well tested in many places around the world and is undergoing some data collection in the temperate rainforest of Washington State.

(Note: In a three year update Terran has reported that there is no moisture behind the cork!).

The risk for us is that we could not find anyone who had used Thermacork on a Tiny House and then moved it on the highway.

Some of the people we spoke to about the idea seemed completely unworried about the material in highway conditions (after all, it survives extremely high winds on building exteriors all the time). Others felt we might want to plastic-wrap the house if it ever gets moved. We’re thinking we’ll probably be safe and wrap it, just as most conventional mobile homes are wrapped for transportation.

This seemed like a reasonable risk to take, as we’re not planning on moving the house often (only once or twice in its lifetime, if needed).

Additionally, the Thermacork allowed us to save a great deal of weight over the normal exterior insulation-batten-siding approach – no matter how we sliced or totalled different materials. Thermacork also had a major advantage for sound: one inch of it cancels as much as 50 dB equivalent.

Most importantly, though, the Thermacork saved us space.

After repeated U-Wert analyses, it became clear how important every inch used for insulation can be in a Tiny House, due to size restrictions. Tiny Houses generally need to be less than 8’6” total width, and less than 13’ 6’ total height for road legal transport in most areas.

Additionally, since we were trying our best to make sure that the structure could be certified as a legal residence (we are now nearing receipt of a Certificate of Residence or Occupancy) we had to hit the International Residential Code (IRC) requirement of 7’ interior space in length and height of all habitable areas.

These factors place a clear limit on how much space there is in a Tiny Home for insulation.

A note on foam vs other insulation: under these circumstances, foam can be tempting. It’s light, it appears to have the maximum R-value per inch of all available insulations save for Vacuum Insulated Panels (VIPs). It can also come in differing forms (spray, board, roll, exterior roofing spray, etc.).

However, even the most trustworthy professionals in the foam industry I spoke with emphasized that spray foam will lose significant R-value over the course of its life.

It will be dimensionally unstable, eliminating its proposed air-sealing value, and potentially creating gaps in wall-cavities over-time. It is expensive. Almost all foam is heavily vapor-closed, and so does not allow breathing of moisture in most building assemblies like ours.

Most of it also outgases for the life of the product, and spray-foam can lead to disaster if minor aspects of the install go astray.

For more information on why we chose to avoid foam in our build, please see 475’s excellent blog series “Foam Fails.”

A final note on our framing design: it could be said that we took a risk by utilizing advanced framing techniques for a mobile design. This has become a commonplace approach among Tiny House builders, but it does require care.

The architect who volunteered to help us, John at Rebuild Studio, as well as the seasoned framer we consulted with, took every opportunity to emphasize that.

We made sure to install metal braces at pretty much every connection point (between floor and wall framing, between roof rafters and sill plates, etc.).

Our framing consultant really did want to see us use 2×6’s – rather than the Tiny House standard 2×4’s – and for a lot of reasons (see the “Interior” section on Windows, Doors, and Interior) we decided to go with that suggestion.

Here are more pictures of the framing.

Roof

If we had anyone nearby who could do dense-pack cellulose affordably (or there was a machine we could rent nearby to do it affordably ourselves), I would have insulated the roof with cellulose to be sure we got the weight balance right.

Aside from the sheer lightness of cellulose, dense-packing cellulose or fiberglass might have also allowed us to save considerable additional weight by removing some of the secondary stick-framing we put in, in order to add additional layers of Rockwool around an interior thermal break space.

There are also fantastic cellulose batts on the market, but they would have cost us about twice as much as Rockwool (due to the fact that we can easily drive across the border into Canada and buy Rockwool near the factory).

I want to highlight this risk, because I would not want anyone else to take the same approach we did, only to find that their building is top-heavy and dangerous.

I have not taken our Tiny House on the road yet, and so I cannot confirm that it will be functionally balanced. Based on our best weight calculations, and the considerable weight of the floor assembly and heavy-duty trailer we built on, we felt like the building would be alright traveling at moderate speeds.

Here on the build site, it has never so much as swayed a millimeter. But I remain agnostic about how this aspect of our build turned out, and we may not know for many years how it will fare on the road.

(In a three-year update, Terran mentioned to me that the house has done well in very high wind storms, but has not yet been moved).

That R-60 roof value was very challenging to reach without foam, we had weight restrictions, and it required some sacrifice in space.

Many Tiny Houses really skimp as much as possible on insulation in the roof and floor, so that they can have enough space for a functional lofted living/sleeping area.

A major factor that encouraged us to go with our approach is that, due to the IRC’s size requirements for habitable spaces, most Tiny House lofts are illegal for sleeping or any other habitation activity.

Knowing that, we were willing to sacrifice a loft. Instead, we made what is essentially a permanent bunk bed – and since one of the main concerns I’ve heard with Tiny Houses is closet space, we made it into an inexpensive pull-out closet.

There would have been no way to make a legal living space underneath.

We could have also gone with the approach of putting the bed underneath a platform living space, and rolling it out on casters (to see how this approach works, see the Minim House.

If I had needed a larger bed, that is most certainly how I would have done it (and I would have made sure to get an out-swing door, rather than an in-swing!)

Floor Assembly

Another aspect of our design that might require some explanation is the floor assembly. We went through a number of ideas for how to create a truly thermally broken Tiny House floor.

Along the way, we also had to face the fact that there were no known ways around using vapor-impermeable materials for the interface between the floor frame and the trailer – at least none with proven longevity.

I really wanted to be sure that the floor had vapor permeability because I’ve seen deconstructed Tiny House floors that had gone rotten after some years due to impermeability issues.

Floors, especially those elevated off the ground and exposed to air and wind, can really have a tendency to deal poorly with vapor drive. They are the coldest assembly in a Tiny House.

After some great advice from many professionals, we decided on using ¾” marine-grade plywood for the underside of the floor assembly – with some added tricks and layers.

Floor Trick 1: We built the floor upside-down, in sections that we could manipulate without heavy equipment. While the marine-grade ply bottom was exposed, we taped all ply seams with Extoseal Finoc, as well as all parts of the ply that would interface with the trailer.

This not only provides a great self-sealing water-proof layer but also enables meaningful amounts of capillary action to wick away any moisture that comes between the floor-frame and the trailer in those interface spots.

Floor Trick 2: We then coated the remainder of the exposed marine-grade-ply-surface with Prosoco R-Guard Cat 5, which was extremely impressive.

As many Passive House Professionals have pointed out, relying upon liquid-applied layers for air and moisture sealing on walls and roofs can be unreliable. Many such layers can fail over time. Also, they are not produced in a factory (like Solitex Mento or Intello) and are essentially “manufactured” on site. This creates significant added potential for failure/error during application and curing.

However, in our case, we were not relying on the Cat 5 for air sealing, since we would be taping all seams by the end of the install.

What we wanted was a thick, durable protective layer over the ply surface that would completely repel water, and be moisture permeable from the interior. CAT 5 fit that description very well: it’s thick, water-immune but breathable, and incredibly strong (almost like dolphin skin when wet).

Prosoco’s amazing field rep emphasized that Cat 5 should always be covered and protected by rain-screens, etc., as it can definitely be damaged.

However, because our application was sheltered and downward-facing, and we were not covering the surface with siding or anything of that nature, we felt all the more confident that we would be able to patch the material over time with a brush-stroke or two anywhere it might get damaged during sitting or road-travel.

We figured we’d just schedule logical times to check the surface and see if it needs repair (zero repairs needed so far).

Although the material should never be exposed directly to the sun and other elements, because we were installing on the underside of a floor-frame and taking the above precautions, Prosoco agreed that this was a feasible approach for our application.

Floor Trick 3: After a lot of consideration, we settled on putting the thermal-break layer for the floor to the interior.

Placing a thermal break to the exterior of a THOW floor frame either left significant thermal breaks (as in insulating the trailer frame), created a danger of decay (SIPS), or other problems.

Placing the continuous layer of insulation inside the building envelope allowed us to not only to ensure we had a robust thermal break but gave us the ability to build our floor sections with 2×8’s (again, without heavy equipment) because we would not need to lift the added weight of wood-fiber insulation board with the sections, during placement on the trailer.

Floor Trick 4: The engineer we worked with said that we should use stainless steel bolts and nuts to be sure we had enough strength, and he gave us a pretty large number to install.

It was a really fail-proof way to ensure connection to the trailer – and will allow the Tiny House to be removed and put on another trailer or a foundation when this trailer reaches the end of its life.

Because our floor frame was so thick, we had to use an extremely long metal drill-bit meant for aircraft, but it was available locally and worked very well (with a lot of elbow grease – Kangaroo Trailers makes a seriously beefy trailer). Dave at Kangaroo was able to get us additional attachment points via welded flanges on the sides of the trailer, and very well-made cross-bars going across the center.

His design also saved significant amounts of weight over many of the other approaches we’d seen – while still keeping a maximum amount of strength on the main frame and the tongue.

We had been hoping to avoid the use of sheet-goods with formaldehyde of any kind on the interior of the structure, so we used tongue and groove pine instead.

Above the pine, we installed the wood-fiber insulation, and above that, we laid Intello Plus and connected it on all junctions with the wall membranes.

This very effectively sealed the pine out of the interior living space. However, we were left with a surface that would have been difficult to install a conventional floor over (i.e. the top of wood-fiber insulation, with relative blindness to the studs and tongue & groove below).

Floor Trick 4: In the end, after a lot of research, we used Marmoleum Click for our finish floor.

Marmoleum makes the only linoleum certified by several international health organizations – and takes great care to ensure that all materials used in their products are low-off-gassing.

Running a simulation of the product in U-wert (using the top-surface, the low-VOC HDF, and bottom cork layer) tested to have acceptable vapor permeability – although we were never able to get official perm ratings from the company.

More pictures of the flooring process here. 

Part III: Air Sealing, Ventilation, and Heating

Because we wanted to avoid drafts, foster dry wall cavities, avoid the formation of mold throughout, and have good control over the interior air-quality of our Tiny House, air-sealing and ventilation were incredibly important to us.

We were extremely happy to find products that worked perfectly for these purposes and had extremely rigorous testing and research backing them.

Air Sealing

We used a carefully detailed continuous layer of Solitex Mento 1000 as our primary exterior air-sealing layer, and vapor-permeable secondary Weather Resistant Barrier (WRB).

We applied a similarly detailed interior layer of Pro Clima’s Intello Plus as our interior air-sealing layer and intelligent vapor control layer.

We then applied Tescon Profil tape for all our window connections to the interior and exterior membranes (taking care to seal and connect the junctions between Mento and Intello). 

We also used Tescon Vana to seal the seams of the exterior sheathing as a back-up, to help ensure we got a good air-seal – since it was our first time around the air-sealing-block.

475 believes in redundancy, and although taping all plywood seams below a layer of Solitex Mento is not a step they suggest, we really wanted to be sure we got a proper air seal, regardless of any novice mistakes.

Along the way, we sealed all seams and penetrations of the interior and exterior membranes with Tescon Vana as well.

Extoseal Encors was used for all the window and door sill-pan details. 

Encors is able to flex and shape itself around corners in ways that are genuinely unbelievable, especially when compared to normal materials – and its self-sealing and waterproofing capabilities are essentially superpowers.

Note: 475 (and most architects) recommend applying this directly to the wood in the rough opening. However there was some disagreement among experts at the time of building.

We also wanted to experiment with trying to save vertical space by using Solitex UM on the roof.

This allowed us to save the inches of vertical space that would have otherwise been taken up with battens, while still allowing moisture from under the roof panels a pathway out from under the standing seams.

We had to take special care when lapping the drip-edges to be sure the moisture would escape on the mesh, as planned, and also had to take a lot of care while installing the roof panels over it, but we all wound up being impressed with the functionality of the membrane design.

Because we had to have some extended conversations with 475 about how to detail this particular process, and we haven’t seen it elsewhere on the 475 blog, we wanted to list the steps here:

  • Install Wood-Fiber Insulation properly over the roof sheathing.
  • Properly stretch, mechanically fasten, and tape the Solitex UM over the wood-fiber insulation.
  • Make sure to properly connect the Solitex UM (or plan so that you can connect it later) to the air-sealing layer over the walls.
  • Be sure that you are placing the edge of the mesh so that it allows water to drip properly over the edge of your roof, and not down behind any part of your wall.
  • Integrate the fabric part of your Solitex UM properly with your wall’s air and weather barriers so that there are no gaps.
  • Follow manufacturer’s instruction for the proper order of installation of the Standing Seam Roof panels, drip edges, etc., while taking the following steps:
  • Each time you fasten any material through the Solitex UM, cut a small slit in the mesh layer above the fabric, to be sure that your fastener doesn’t catch a strand of the mesh, and leave a pathway for moisture to travel along the fastener, and below your fabric.
  • As you place the roof panels, fasten them through backer plates to ensure that the fasteners do not damage or puncture your insulation board.

A final note on Solitex UM: If you’d like to experiment with saving wall space, you can also use this on the exterior of your walls, instead of battens, and apply your siding directly on top of it.

Here are some detailed pictures of the roof install. 

Ventilation

For ventilation, we went with a pair of Lunos E2 units, and an eGo for the bathroom fan.

The units provide pressure-balanced ventilation, and the upper end of their CFM capacity is more than what we wanted for the tiny space, even given how much I appreciate fresh conditioned air.

Despite that, I would not recommend using just the E2 units without a proper bathroom fan of some kind. E2 pairs are not rated for enough moisture to be used in a bathroom.

In the warmer shoulder months when it’s often too cold or wet to comfortably open a window, and too warm for the air to tend towards dryness – it’s really important to get shower moisture out of the bathroom effectively.

Using both the E2 and a bathroom fan (especially the eGO) made the humidity manageable.

A bathroom fan also ensures that unpleasant bathroom odors do not become a problem.

(As an important side note: Lunos HRVs should always be located at least 1.5’ from the ceiling in any location. These are often not placed correctly.)

Three year update:

I had some bad luck with the E-Go as a bathroom fan in a tiny space. The small channels in the ceramic core got moldy, and there’s no way to clean them. Luckily the problem was isolated.

There are a lot of factors that could have caused this, and it’s possible I could configure things to make sure it won’t happen again, but as of now, I can’t recommend the E-GO’s for THOWs. 

It’s important to me that I be able to clean all the air-flow-related appliances if needed. It’s possible to clean the E2’s very effectively – which I’ve done now, on multiple occasions. 

Luckily, all the Lunos products are easy to remove from their install tubes and replace them with any other Lunos product. so I replaced the E-GO with a normal bathroom exhaust fan from Lunos.

Dehumidifier

With the smallest 25-pint Kenmore Dehumidifier (Note from Corinne, they no longer make this size but this is another good dehumidifier) the house has been able to maintain 50% humidity or below at all times, even during the wettest moments of the summer months (most of the time the dehumidifier is not needed, but when it is, it clears out the humidity quickly, and much more effectively and reliably than any of the smaller options I looked into).

Here is a good and well-priced humidity meter. I have several thermometers with humidity meters on them – some positioned high, some low in the house, some floating so I can place them in corners or under surfaces to check levels everywhere. 

Range Hood

The final piece of the ventilation picture was a 24” recirculation range by Summit. I had to remove their foam filter (which was supposed to be what caught non-oil food-particulate, but was shockingly diffuse, and wasn’t even cut to the right size) and replace it with cut-to-fit carbon. I was happier with the carbon than a cheap foam filter anyway.

Three year update:

At first but we used the mini-split circulating air an E.L. Foust 160R2 air-purifier, and the Lunos units running we were able to manage with this set up. But we did change this out to a vented range hood.

I should have installed a vented range hood to begin with — one that was sized large enough, and close enough to the counter, to ensure capture of all cooking vapors.

I wound up having to do this over time — the recirculation hood simply allowed too much humidity to stay indoors, and overloaded the Lunos units with more moisture than they could handle.

After consulting the technical teams at Lunos and 475, I went with a high-quality Vent-A-Hood unit that was several inches wider, and deeper, than the cooking surface, and installed it about 18″ above the cooking surface (shockingly, that’s the minimum recommended height for most high-quality hoods. And it works well for me.)

They had very specific air-flow requirements for the hood I should get, given the nature and size of the space.

Because of the air-tight construction, a vented hood absolutely requires make-up air – and both 475 and the Lunos technical teams assured me that the E2 units could handle what I needed. 

If anyone goes with this approach, make sure to place the Lunos E2 units on walls that are opposite to the kitchen vent hood — so that there is no chance of them sucking kitchen exhaust back into the house.

I’ve lived in tiny houses before that became very moldy as a result of not being able to effectively vent and/or filter the steam from cooking – and the food particulate within it that creates the odors.

Heating and Cooling

For heating, we decided on an LG Artcool Premier mini-split heat pump, which is LG’s highest efficiency model.

Mitsubishi makes the lowest BTU output model on the market at 6,000 BTU’s, and their models have fantastic quality and durability. I have relatives who’ve owned their units for years now and have also made many calls to local HVAC companies, as well as Mitsubishi and Ecomfort’s customer service staff.

All the agents I spoke with were very candid about the different brands and models.

Given all of that, as far as well could tell from initial research, the smallest Mitsubishi unit seemed like the best for tiny spaces. So why did we choose the LG Artcool Premier?

It turns out that even though the smallest LG Artcool Premier model puts out 9,000 BTU, the inverter LG uses allows the unit to step down heat output to just a bit less than the Mitsubishi Unit (at least at the time of my research, that is what both companies confirmed for me when I contacted them about the numbers).

This actually put the LG unit closer to the number the PHPP gave for the total BTU’s we’d need to heat our house (PHPP will tell you exactly how large your heater needs to be, among many, many other useful things).

So in this case, the LG unit will be able to almost match its output to our exact needs, under any circumstance.

As it turned out, the small amount of research I’ve seen from the Department of Energy indicates that having units be oversized for the space and unable to step down to the given needs, is a major factor decreasing efficiency.

Another factor is that the Mitsubishi unit automatically shuts off at around -13 F according to the submittal. The LG unit does not have an automatic shut-off.

Field reports from users as well as the company would indicate that it can continue to put out enough heat to heat a tiny space like ours down to as low as -20 F.

So in the end, the fact that our unit puts out 9,000 BTU is not a problem due to the inverter flexibility, and the extra BTU capacity also gives us some extra breathing room to keep using the unit as temperatures drop into negative digits.

Beyond all that, the LG was significantly less expensive, which I appreciated. You also get some additional items that cost extra with Mitsubishi (like the drain-pan heater).

The folks I’ve spoken with who’ve installed these units have emphasized that they tend to have very few problems – IF, as with any brand, they’re properly installed by a professional, and well maintained.

At this point, we can heat and cool (and ceiling fan!) the house for around 200-300 watts in most cases. This is amazing.

The dehumidification function is disappointing, and in general please remember to use the “self-cleaning” setting on the remote if you buy one.

Running A/C and dehumidification on these units can lead to them developing some mold after a while if you don’t run the fan enough to dry the fins out. 

The “self-cleaning” setting does that to some degree, but I try to run the fan function as much as I can, and that also keeps really good air-mixing going in the house (and helps make up for the fact that we placed the Lunos Units too close to the ceiling!)

One final note about mini-splits: our installer seemed short on time, and insisted that he wanted to put the indoor unit on the same wall as the exterior compressor.

This is not what we had previously planned on, and came as a surprise.

Unfortunately, this meant that it was not only right over the foot of the bed, but would be somewhat obstructed by the only cabinet we had installed.

The location worked out fine, and it heats the space wonderfully regardless. However, I hope that if you’re thinking of getting a mini-split for your Tiny House, you might be able to account for putting it in the spot that will be most straight-forward for the installer (and least expensive for you).

By having the lines from the indoor unit come straight out the wall above the outdoor unit, we saved him an immense amount of time on working with the copper lines, etc..

Part IV: Windows, Doors, Interior and Framing Details

Windows

Windows, for a Tiny House on Wheels (THOW), were items that we had to research and reflect a great deal on.

There are many different standards for what counts as “high performance” windows, depending on who you’re talking with.

For a certain section of the market, Marvin and Andersen are considered high performance and efficient. We’d had experience with them in the past, and although we were pleased with the workmanship and quality of service, they always became drafty in our region and could be frigid to sleep near.

In sections of the truly high-performance market, we found triple and quad-pane windows that were of incredible quality, but also way outside of our weight allowance and budget.

Luckily, we found that there is a small section of the Passive Haus and high-performance market that has been working with Heat Mirror technology – which is essentially a special kind of heat retentive film used in place of ordinary sheets of glass.

It is cost-effective and comes close to being in the same range of efficiency as panes of glass.

However, after speaking with some fantastic (and very honest) engineers at companies with some experience in Heat Mirror use, it sounded like most of them hadn’t really figured out how to make the technology reliable in the long-term.

Right around then is when we were referred to Alpen High Performance Windows.

Alpen (formerly Serious Windows) has arguably more experience with Heat Mirror technology than any other company in the industry. They’ve learned how to secure and seal the Heat Mirror film properly, as well as suspend the film so that it does not sag or cause distortion over time.

They’re accustomed to using Heat Mirrors between glass of varying thicknesses and types, for all applications – and they do so for both triple and quad-pane units. This saves enormous amounts of weight.

Their manufacturing takes place in-house at their factory in Colorado – so they are able to have excellent levels of quality control over both the process and the product.

After a lot of pricing and research, I honestly cannot recommend any other company for high-performance windows to be used in THOWs.

They were also able to work with me to eliminate PVC from the windows I bought (replacing PVC glass stops with aluminum ones – the rest of their windows are made from an amazing low-toxicity fiberglass).

I found the PVC used in many PH windows to be a major problem in a tiny space, and many companies unavoidably include PVC and do not offer any flexibility to allow you to eliminate it.

All of the people I spoke with at Alpen were wonderfully kind, and either had the information I was looking for or readily put me in touch with someone who did.

If you’re looking for PH Certified Windows that will fit into the weight constraints, efficiency standards, and budget for a Tiny House, I just can’t imagine buying anything else.

For those who are very sensitive to off-gassing VOCs from window seals, there will be some of that with Alpen windows – as with any window.

People like us just need to plan some time in for things of that nature to off-gas before moving in. It didn’t take long before they were fine for me.

I’ve never felt uncomfortable in front of one, even in -20 F weather – and I haven’t yet seen even a speck of condensation on them (although the space has been extremely dry during the winter much of the time, often sub 30% humidity).

Here are more photos of the window install.

Doors

Researching high-performance doors for a tiny space was similarly challenging.

Again, weight was an issue for the extremely high-quality PH certified doors I saw – we just wouldn’t have been able to balance it properly, or account for it in the overall weight budget.

They were also incredibly expensive and outside our financial budget.

Due to a recommendation from Alpen, and other folks we spoke with, we began looking into local ProVia dealers. They make high quality, well-crafted steel and fiberglass doors with R-values around 5, solid air-sealing values, and options for quality multi-point locks.

Just about a year before we contacted them, ProVia began manufacturing what they’re calling the “Embarq Door.” They claim that it’s the highest R-value unit on the US market, and many reps at their company seem to consider it to be the ultimate in high-performance entryways.

Although I feel someone at the company should inform these employees that there is an entire world of PH doors out there – many of which blow the Embarq away in pretty much every category.

I hope more people get a chance to look into it and see if it’s a good fit for their project. It has some improvements to make, but it’s a very high-quality American made door, for a decent price (depending on where and how you buy it).

The Embarq door is R10. ProVia built it more or less like a vault-door: with a tapered interior edge.

Based on our research into door options, it came in at between ½ and ¾ the cost of a certified PH door, depending on the given model and quote.

The Embarq makes use of ProVia’s impressive Signet fiberglass technology – which is not only light but can also imitate a number of different wood grains, to the point of being almost indistinguishable from wood from six feet away.

On the downside, ProVia hasn’t yet figured out how to use multi-point technology in the door (due to the vastly increased thickness over their standard doors).

Because of this factor, and the fact that they’re still tuning their manufacturing process for such a thick slab, the air-sealing figures suffer a bit compared to their normal doors – despite the multiple layers of seals they use.

They seem to be figuring out the manufacturing process and how to work around the slab thickness and seals, which can make for tricky installs – especially if you’ve ordered a wide-jamb door, as we did.

For our interior bathroom door, we picked up a free slab with hinges from Craigslist. I apologize to those who were hoping for something prettier!

Interior Framing Details

On the interior of our envelope, after much debate and reflection, we decided to go without a service cavity in the walls. This is not a choice that we made lightly, and I wish we’d been able to include one.

Because we had the space, we were able to use a service cavity in the ceiling – and we packed as much electrical into that as we could, and fit 100% of the plumbing into the interior bathroom and countertop space.

For what little wiring was left over in the exterior walls, we settled on surface-mounted outlets which allowed us to avoid large holes in the membrane.

Air-sealing a Romex cable is pretty straight-forward with Tescon Vana and it saves a lot more air-leak risks than a larger hole.

We did use one air-sealing outlet-box from 475, and it was awesome (i.e., sleek, space-saving, easy, effective, etc.).

If I had the chance to go back to the electrical phase, I’d just use the air-sealing boxes everywhere instead of the surface mounts.

If I had a chance to do the whole project all over again, I would want to do a full-on service cavity in the walls.

Here are more pictures of the electrical.

Using a service cavity is the best way to assure a fully intact and functional interior membrane, and it just makes everything in the finish phase more straight-forward.

In our case, we would have either had to trade the 2×6’s we used (to increase structure and insulation) for the service cavity space, or make the interior an illegal living space by making it smaller than 7’, side to side.

We made the best choice we could at the time, and I was very focused on trying my best to get as efficient and moisture-sound as we possibly could.

As an additional note on where I was coming from, no matter how I configured it, U-Wert consistently showed us significantly better efficiency and moisture numbers for a 2×6 wall cavity with 2” of exterior insulation, than with 2” of exterior insulation, 2×4’s and a 1.5” service cavity.

I don’t know if this was just a glitch in U-Wert, but especially the moisture performance calculated as clearly superior, even when using a 2.5” service cavity.

I think this might be due to the fact that the inboard membrane had all of the insulation to the exterior of it so that the total amount of wall insulation was not broken up by a second set of framing members, and the membrane.

U-Wert also showed a clear improvement in moisture performance when the service cavity was left un-insulated, so I imagine that the additional insulation on top of the Intello created more of a temperature difference between the inside air and the Intello’s interior surface, which made for greater condensation risk there in the winter.

I hope those who are much more in the know than myself, and with expertise in WUFI, will chime in with their thoughts.

Obviously, both wall cavity sizes are far, far smaller than any truly Passive House in the Northeast. Based on my tinkering with U-Wert, I do not imagine anyone with a Passive House in this region would see moisture dynamics of that kind in their assemblies, due to the much larger amount of insulation exterior to the Intello.

The U-Wert analyses certainly support that idea – and I can see that principle at work in how the numbers for our roof assembly worked out.

Because of the greater amount of insulation exterior to the Intello membrane, we could have easily insulated the service cavity without much condensation risk.

However, given that we wanted to squeeze as much insulation into the walls as we could, we just couldn’t see making wall service cavities and not insulating them.

To moderate the risk we faced by not using a service cavity on the walls, we worked with John Kingsley, at Kingsley Woodworking in Ithaca NY, to come up with a creative approach.

John was the only person we found who could mill us ½” Poplar T&G panelling (or ½ panelling in any wood species). He did a beautiful job milling and sanding it. Because John knew we were trying to save weight, he mentioned to us that he could remove a small rectangular portion of wood from the back of the panelling, without compromising the structural integrity.

He calculated that this would save us quite a significant amount of weight over the whole structure. Once we saw the kind of thing he was talking about, we also felt like the extra space behind our panelling might provide a least a little bit of additional room for moisture and air exchange, which helped us feel a bit better about not having a service cavity.

Because we knew at least some of the paneling would have to be in direct contact with the Intello during its least permeable mode, we made sure to paint all four sides of the paneling boards with highly permeable Romabio mineral paint.

Romabio felt that the paint did a good job of protecting wood from liquid moisture, while at the same time remaining vapor open.

We won’t know whether this approach worked until some years have passed, or we cut a paneling sample to see what it looks like on the underside.

Note: in a three year update, Terran reports that the walls have been opened for inspection and it’s been dry as a bone!

There were a lot of approaches we took with the interior, in order to try to maximize the efficiency of the space or minimize weight while maintaining high-quality.

Countertops

Eco Supply Center, which was the source of our Facade-Grade Thermacork, also very kindly walked us through the process of buying and DIY-ing Richlite for our countertop.

Richlite was by far the best material we found for this purpose, after a lot of searching and ordering samples.

Richlite is 0 VOC, waterproof, far more durable than wood, and weighs a tiny fraction of stone or other high-quality non-paper-based solid-surface options.

Cutting and installing it ourselves was a little daunting, but between the amazing assistance from folks at Richlite, and the great people at Eco Supply Center, we were able to do it (at least to our standards!).

In the end, we were able to use a totally normal saw blade for the cuts, but it did need to be high-quality, and sharp – at least in the beginning.

After making our cuts, the Richlite dulled our blades to the point of them being basically useless. We certainly took that as a testament to how robust the material is, and it was great to be able to DIY it since most other non-wood countertop materials must be cut with professional equipment.

Part V: Water and Electrical

Water Heater

The folks at Stiebel Eltron were an incredible resource for water heating. I searched an awful lot for a hot-water heater that would allow us to avoid plumbing propane (and re-filling propane tanks) and would give us on-demand levels of efficiency for the small amount of hot water I needed.

All the on-demand electric water heaters I found required much more amperage than we would be able to run to the THOW, even the amazing range of on-demand units that Stiebel Eltron makes (their lower-flow, lower-power sink units just weren’t designed to put out enough water for showering).

After using an incredibly effective little 6-gallon water heater in India, I started looking into similar options on the US-market but found them to be generally unreliable based on reviews.

They were disappointingly inefficient.

They were also not built for long-term serviceability and became trash as soon as most anything needed to be replaced.

Stiebel Eltron makes by far the most efficient small-tank water-heaters on the market, and during my search, they released their 6-gallon model. It is serviceable across the board, and replacement parts are available through Stiebel Eltron for anything you might need.

In my experience, with a low-flow showerhead from Niagra I can have all the water I need to take a more-or-less normal (though by no means long) shower, so long as I make sure the tank is up to temperature before I start.

It takes some care and practice playing with the hot and cold, and my preference is to keep the tank temperature right about 115 through most of the day, then turn it all the way up before taking a shower, and wait for it to get up to temperature before jumping in (there is a light on the side of the unit so you can tell when it’s running, and when it’s up to temperature).

The unit has been extremely quiet and draws 1300 watts when in use (according to the literature, it has around ½ KW standby usage per day, at 120 F, if you leave it on all the time).

That was low enough to fit within the bounds of the underground electrical service we were able to run to the house, and I am extremely grateful for that.

Electrical

Along with an induction cook-top, and the previously discussed heat-pump mini-split, everything fit just fine into a 50 amp service.

With some care, we could run the house on an extension cord in the future if needed – and we’re now all set to run on renewables like solar, if I ever have the money for them.

After talking with a number of people in the industry, it seems like with decent sun exposure, we would need very, very little in the way of a solar array to off-set the entire foot-print of the THOW.

And here is one last album with general construction details!

Closing Thoughts

I hope that we might have shared something here – either through the text, video, or pictures – that will be helpful to others.

There are so many good intentions in the Tiny House community, and I worry that far too many people wind up with spaces that fall short of what they expected in terms of comfort, health, and efficiency.

I’ve been inspired by folks who broke out of the main-stream to experiment with addressing those problems – like Robert and Samantha at Shedsistence, and Leaf House in Canada.

I hope we can all work together to make tiny structures live up to their potential, and become healthy, comfortable, efficient, affordable, and legal spaces for people to live.

-Terran (owner/builder)

This post was written by Terran, whose expertise was self taught and informed by multiple building science experts like the engineers at 475, and John, an architect at Rebuild Studios.

To donate to help Terran cover his living expenses you can find more info here.

healthy home build consult

Corinne Segura is a Building Biologist Practitioner with 6 years of experience helping others create healthy homes.

Did you find this post helpful? If so you can donate to Terran to help him with living expenses.

Filed Under: Mold-Free Building, Tiny Homes and Trailers Tagged With: mold free building, tiny homes and trailers

Building a Mold-Free Tiny House

December 24, 2016 by Corinne 13 Comments

Building a Mold-Free Tiny House 

This article will discuss preventing mold in tiny homes that are custom built.

Usually on wheels, but much of this could apply to lane houses and other tiny homes not on wheels (though I don’t discuss foundations here). This will apply to some prefab but not all types.

This post contains affiliate links to products that I use and recommend. Upon purchase, I earn a small commission at no extra cost to you.

Major problems with tiny houses that cause mold:

Re-doing my insulation
  • Very few people hire an architect, engineer or other building science expert to design the system.
  • Many tiny home companies are new and the builders lack experience or are not experienced enough in all aspects of building (from plumbing to roofing, to installing heat pumps, to insulation, and moisture management).
  • The DIY movement is a problem because the size of the home makes it seem like you can do it yourself, yet you still need all the knowledge of all the contractors: electricians, plumbers, roofers, architects etc. to build a house. The size of it does not necessarily make it simple!
  • DIYers ofter learn from other DIYers via the internet, copying others’ mistakes.
  • The movement is new and it can take 10 years for some mold problems to show up.
  • Most tiny homes do not need to follow building codes. Almost anything goes in most places, resulting in poor building practices.
  • Homes are built in one climate and shipped around the US and Canada to other climate zones where the moisture management system may not fulfil its function. Owners may also move the house to a different climate zone. 
  • Only one year warranty on many houses will not be long enough to cover mold issues. 
  • Many tiny homes I have seen have simply invented wall systems that would never be used in a regular house. 
  • I have seen major problems with the moisture management systems such as vapor barrier errors, and smaller but still problematic practices like lofts built with mattresses right on the floor with no ventilation, and inadequate exhaust fans.
  • Lack of attention to detail that comes from inexperienced builders or those not concerned about mold.
  • Building by prioritizing non-toxic materials over building the correct moisture management system (because you remove or replace a part of the system with something non-traditional).
Condensation on my tiny house roof cavity

When I first set out to build my tiny house I was mostly concerned with choosing healthy materials that were 0-VOC.

It was only after I took the house apart (almost completely) to fix the problems my builder made, that I realized the extent of knowledge needed to build a mold-free home.

I thought you just leave the construction details up to the contractor, but my builder (Ben Garratt, Tiny Healthy Homes) made a long long list of mistakes.

I lost 100K dollars, my health and housing stability needed to stay healthy and on budget.

From interviewing and working with dozens of contractors in my area, I have found one out of a few dozen who was knowledgeable and detailed enough to renovate the house in the correct way.

The two most important aspects of designing a mold-free tiny house are:

  1. Have an architect (or other building science expert) who specializes in mold prevention design the moisture management system. This is everything from the wall system to the roof, the floor, and the ventilation. They will also need to take into consideration which materials you can and can’t use to design the system. Take the time to do this in detail before you hire your tiny home builder. I can help with consulting on materials at this stage because the architect needs to know which materials can and cannot be used/tolerated.
  2. Extremely detailed supervision. I have fixed everything from my bathroom fan to my walls and roof. Taking my attention away from the project for more than an hour led to mistakes by the contractors who simply do not care about mold prevention. Even if you find a good owner, that person leaves the work to his laborers or subcontractors who are not well supervised. Here you can either hire someone extremely competent to supervise, or you can supervise yourself. If you supervise yourself, take the guidance from your architect, and learn the basics in order to follow those guidelines (or you will be calling him or her every few hours). Make sure the builders have a very detailed plan of how you want things done so that when you come into supervise you are staying on plan. There may be a clash of egos here, but you need your house done right and most contractors do not have the right skills. 

Of course, choosing the right expert to guide you is also important, so before you do that you should be aware of a few different ways to manage mold that are popular and get a few opinions before you decide on hiring someone.

Here are a few different systems:

  • Passive house design – Passive house design is a very detailed system that uses a lot of calculations to manage the moisture in a scientific way. You can check out 475 to learn more about this. 
  • Breathing walls 
  • Walls with vapor barriers – Learn the basics on vapor barriers and what smart vapor retarders are
  • Wood frame houses versus metal-framed houses.
  • Building with SIPs.

Here are a few terms and ideas to learn about so you can follow along with your expert:

  • Flashing of windows and doors – the instructions on this are fairly simple and yet they are often not followed precisely (they need to be!) 
  • Taping house wrap – there is a controversy about whether to tape the horizontal seams
  • Rainscreens
  • Solar vapor drive 
  • Vapor barriers and condensation
  • Insulation types and their permeability 
  • Perm rating of a material/barrier
  • Air barriers versus vapor barriers
  • Ventilation – proper exhaust fans, ERVs, HRVs, and dehumidifiers
  • Exterior foam insulation method
  • Steel frames versus wood frames
  • Zip systems instead of house wrap

Do not attempt to become an expert on these topics from reading about them online. Though there are more resources and online courses available online now.

You want to be informed so you can choose a good architect and understand the system they are designing for you.

You may also need to learn enough to supervise the build.

Some basic mistakes you can avoid to keep your house as mold-free as possible:

Slats in my loft were a very good idea
  • Window and door flashing not done in a detailed way. Also, beware of 0-VOC peel and stick window flashing which doesn’t fit most codes and is not recommended by the companies themselves for the rough openings. I have also seen windows flashed with house wrap tape and not proper peel and stick flashing.
  • Silicone and other caulks skipped where needed on the exterior due to chemical sensitivities.
  • Having air leaks into the wall cavity.
  • Housewrap not applied to spec –  including the overlap and how it is taped.
  • Roof not vented properly (there is some debate here between passive house design and most builders) or double vapor barrier issues in the roof.
  • Putting the vapor barrier on the wrong side.
  • Planning the house to be used with heating but not planning for AC.
  • Exhaust fans over the stove that don’t vent to the outside. Exhaust fans in the bathroom that could leak moist air into the ceiling. The fan I used is pictured (doesn’t leak moist air). (As an Amazon Associate I earn from qualifying purchases through the Amazon links.)
Proper exhaust fan. Click pic for link
  • Inventing a new wall system that is not normally used. Make sure you understand your wall system and which direction it dries to. Don’t skip on things like rain screens (if that is the system you are using) just because it is a tiny house. 
  • Not having a professional plumber install your plumbing system. Or reusing old plumbing pieces that could fail on you. 
  • Pipes not designed and winterized for the climate causing them to freeze and burst. Not providing the cold and hot water a low point to drain outside. If the power goes out you will need to drain them. You may also want to drain them if you are away. 
  • Using wood that doesn’t hold up well to humidity in the framing.
  • Putting your mattress directly on a solid surface with no ventilation under it (use slats or a box spring).
  • Using natural latex. See my warning here. 
  • Not using a properly sized drainage line on a heat pump. Know how to flush it out, this tends to get clogged with mold.   
healthy home build consult

Corinne Segura is a Building Biologist with 6 years of experience helping others create healthy homes.

Buy Me a Coffee at ko-fi.com

Did you find this post helpful? If so you can buy me a coffee to support the research behind this blog. Thank you!

Filed Under: Mold-Free Building Tagged With: mold free building

An All Metal Tiny Home

July 30, 2016 by Corinne 12 Comments

Here is the tiny house being built for my client right now by Tiny Green Cabins. The house is made with no wood whatsoever, including plywood and OSB! This is made for someone who cannot tolerate wood of any kind. She is extremely sensitive to offgassing and mold. 

This post contains affiliate links to products that I use and recommend. Upon purchase, I earn a small commission at no extra cost to you.

Here are the specs:

Size is 8’ x 20’ x 12’-5 1⁄2” tall, with an approximate weight of 9k GVW.

The trailer is a custom welded steel channel beam trailer.

There are options for the paint used on the trailer.

Steel Underbelly 2 x 4, 16 gauge joists.

The cold-formed steel joists are bolted to the trailer frame.

Walls are framed with 2 x 3 18 gauge cold-formed steel studs @ 19.2 on center, fabricated with screws and welded connections. 

Rain screen (furring) is made of metal (Rain screen in important in case moisture does get into the walls).

Roof structure is 18 gauge cold-formed stacking above joists, fabricated with screws and welded connections. No wood used!

The loft has metal floor sheathing. The kitchen has a stainless steel sink with metal cabinets and countertops.  Other countertops options can be considered.

For the bathroom there are different options – you can have RV hook-ups or a composting toilet and greywater system. (Nature’s Head is the best composting toilet. Others like Sunmar have major issues.)

There are a few options for windows. I prefer aluminum, but they cannot be sourced everywhere. There are other options in my window post that people tolerate well. Typar zero-VOC window flashing is being used.

Fabral smooth painted steel to wrap the exterior walls, and Fabral “w” metal roofing for the roof. Metal at walls is riveted and steel roof and trims screwed. Fabral should be tested first to make sure the paint finish is tolerable. Other metal finishes are available with different brands.

Ceiling is corrugated steel

Interior walls are Fabral steel attached with screws. The interior comes in different colors, or can be painted later with metal primer and paint. Caulking is used to prevent water vapor from entering the wall cavity.
Metal flooring is 2 layers of 18 gauge steel layered. Foam is used as a thermal break and insulation.

Doors are metal and glass.

Insulation options are XPS foam or foil-backed polyiso. Foam is being used as exterior sheathing/thermal break as well. Other materials could be considered for insulation but rigid foam was our top pick here. Tyvek tape is used to seal the sheathing if tolerated.

They also used caulk on the inside side for an extra barrier to water vapor entering the walls. (This is a double vapor barrier – note the risk. Please consult with an architect if you can only tolerate metal and foam).

Heating and cooling a 12-15,000 BTU inverter heat pump, Daikin LV series or Mitsubishi hyper-heat models installed by an HVAC company is recommended. Other heating options such as wall mounted electric heaters or propane RV heater/AC combos (off-grid) could be used. Another propane option that is tolerable is a direct vent heater.

For a hot water heater, we are using propane on demand. This is the best way to go for water to keep the house to 50 amps or less.

Exhaust fans are very important in an all-metal house to keep the humidity as low as possible. In the bathroom, it should be exterior mounted as to not leak moist air into the ceiling. An ERV could be a good option if you have a composting toilet (this depends on your climate as well). In the kitchen, the exhaust fan needs to vent to the outside. A dehumidifier may also be needed if condensation forms on the walls or the mattress becomes damp (do not put a standard mattress straight on the ground).

For appliances, a propane fridge should be considered to reduce electricity needs (2-way or 3-way refrigerators can be good depending on your needs and if you are incorporating solar).

An apartment-sized stove can be used or else a small convection oven with a cooktop. If you can tolerate propane or alcohol stoves those can be considered for an off the grid house.

Flooring can be left as metal. Tiles can be considered although this would add considerable weight. Natural carpet or rugs can be considered as well to cover the metal.

Corinne Segura is a Building Biologist with 6 years of experience helping others create healthy homes.

I can help you work with your builder to come up with a customized list of materials that will work for you and your tiny house. Please see my consulting page for more details and contact info. 

Thanks to Luke Skaff, electrical engineer, for help on the technical aspects.

Always consult with an architect or engineer on moisture management in your building envelope.
SaveSave
SaveSave

Filed Under: Mold-Free Building, Tiny Homes and Trailers Tagged With: mold free building, tiny homes and trailers

Primary Sidebar

Follow along for the latest!

  • Facebook
  • YouTube

ABOUT ME

Hi, I’m Corinne, I am a Certified Building Biologist Practitioner with 6 years of experience helping people create healthy homes.

More about me…

Footer

Categories

  • Healthy Building
  • Healthy Interiors
  • Mold Avoidance
  • Mold-Free Building
  • Mold-Free Interiors
  • Tiny Homes and Trailers
  • Uncategorized

Amazon Affiliate Disclosure: As an Amazon Associate I earn from qualifying purchases.

Privacy Policy, Disclaimer, Disclosure

Do Not Sell My Personal Information

Resources

Business inquiries

Copyright © 2021 · Corinne Segura | My Chemical-Free House Consulting