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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
    • Pipes
    • Alternative Building Systems
    • Non-Toxic Prefabs
    • Building for the Chemically Sensitive
    • How to Test Materials
  • Healthy Interiors
    • Flooring
      • Gym Flooring
      • Flooring Underlayment
    • Kitchen Cabinets
    • Countertops
    • Mattresses
    • Sofas
    • Leather Furniture
    • Desks and Chairs
    • Sealers
      • Paint
      • Mineral Paints
      • Linseed & Tung Oil
      • Natural Wood Pigments
      • Natural Plaster
      • Natural Countertop Sealers
      • Concrete Sealers
      • Wood Finishes
    • Bathroom
      • Bathroom Vanities
    • Rugs
    • Wallpaper
    • Kitchen Appliances
    • 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
  • Healthy exteriors/gardens
    • Decking Materials
    • Deck Stains
    • Deck Cleaners
    • Exterior Paints
    • Sealant for Concrete Birdbaths
  • 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 that New Car Smell
    • Building for Chemically Sensitivity
  • Mold-Free Building
    • A Detailed Mold Preventative Build
    • The Causes of Mold in Tiny Houses
    • How “High Performance” can Help Prevent Mold
  • Mold-Free Interiors
    • Mold Testing Overview
    • Air Purifiers for Mold
    • Ozone to Kill Mold
  • Mold Avoidance Paradigm
    • 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 prevention

Hempcrete for Mold-Safe, Healthy Homes

November 3, 2021 by Corinne 1 Comment

Hemp can be used in building homes in many ways but building with hemp is very different than building with conventional construction methods.

Hempcrete can be tamped into board-formed walls, used as premade bricks, sprayed into cavities, or formed into precast panels.

It acts as insulation and as an interior and/or exterior surface, though it is not load-bearing – you still need a wood frame.

This article will review all the ways that hemp can be used to build a healthy home and is an investigation into whether it’s mold-prone.

[Read more…] about Hempcrete for Mold-Safe, Healthy Homes

Filed Under: Healthy Building Tagged With: Healthy building, mold prevention

Non-Toxic Decking Material Options

August 15, 2021 by Corinne 13 Comments

This is a complete guide to non-toxic decking – types, materials, additives, and brands.

For most people, the main choice is between composite decking and solid wood decking. For the chemically sensitive you will have to get samples yourself of the decking materials as well as the stains needed for real wood – as this choice is very individual.

The long-term benefits of not having to do any maintenance on composite decking can outweigh the initial concerns.

There are also some more unusual options to choose from like aluminum decking.

[Read more…] about Non-Toxic Decking Material Options

Filed Under: Healthy Building Tagged With: Healthy building, healthy exterior/gardens, mold prevention

Review of Boxabl Prefabs (Home of Elon Musk)

July 12, 2021 by Corinne 38 Comments

Review of Boxabl SIPS Prefab House

The company Boxabl has created a metal SIPs (structurally integrated panel) house that has caught a lot of folks’ attention.

The main reason it has gone so viral is that it promises it all – fast, easy, cheap, resilient, and healthy.

My job as a Building Biologist is to review homes for durability, indoor air quality and resilience to mold.

It may be cheap and fast, but is this home a durable and healthy home?

[Read more…] about Review of Boxabl Prefabs (Home of Elon Musk)

Filed Under: Healthy Building Tagged With: Healthy building, mold avoidance paradigm, mold prevention

Non-Toxic Insulation: A Complete Guide

April 5, 2021 by Corinne 188 Comments

There are so many excellent choices for non-toxic, healthy, green insulation, there should be one to fit everyone’s needs.

Look out for Greenwashing

There are many new options that claim to be “green” “soy-based” or are formaldehyde-free – this does not mean that they are VOC-free or safe. Look very closely at what’s in it. Also, flame retardants and mildewcides are not counted as VOCs.

Green Certified?

On top of that, certifications are not that useful: almost every insulation now qualifies as GreenGuard Gold, which for sensitive folks is not enough information.

The post includes the best of green non-toxic insulation and includes a cost comparison as of 2021.

[Read more…] about Non-Toxic Insulation: A Complete Guide

Filed Under: Healthy Building Tagged With: Healthy building, mold prevention

Non-Toxic Grout and Thin-Set Mortar

March 15, 2021 by Corinne 67 Comments

This post covers all of the materials you need to complete a tiling job without the use of toxic materials that offgas VOCs.

Luckily this is not too difficult to accomplish if we stick to the right kinds of products.

When tiling, first we lay down a mortar which is almost always a thin-set (not thickset anymore). We might need to use membranes or special backer boards depending on the project. After the tiles are laid, the grout is applied between the tiles. A non-toxic grout sealer is the final product needed.

[Read more…] about Non-Toxic Grout and Thin-Set Mortar

Filed Under: Healthy Building, Healthy Interiors Tagged With: Healthy building, healthy interiors, mold prevention

Mattresses for the Chemically Sensitive | A Complete Guide for 2023

February 21, 2021 by Corinne 167 Comments

This post started out with my journey to find the best mattress that suited my own extreme sensitivities. There are so many more options now. Still, many I don’t think are good enough.

We will look at my top picks for the best healthy spring mattresses (no latex or polyurethane) with price comparison (2023), all wool mattresses, and other futons, and why I don’t use natural latex.

There is no all-around “best” mattress for those with sensitivities. Sensitive folks can have a hard time with any of the following main materials used: cotton, wool, hemp, natural latex, and polyurethane. You will have to find out which materials work for you.

The article includes a look at more unusual options for those who don’t do well with any of those main materials, or who just want something simple.

[Read more…] about Mattresses for the Chemically Sensitive | A Complete Guide for 2023

Filed Under: Healthy Interiors, Mold-Free Interiors Tagged With: healthy furnishings, healthy interiors, mold prevention

Non-Toxic Flooring Underlayment

July 23, 2020 by Corinne 41 Comments

There are a variety of underlayments used under wood floors, click-together floating floors, as well as carpet and tile.

Underlay can serve various functions like cushioning, sound deadening, leveling, uncoupling, and moisture resistance.

The following underlayments are relatively high in offgassing (too high for me):

  • Polyurethane foam
  • Rubber
  • Vinyl
  • Most cork underlayments, except the ones listed here

This post goes over the best non-toxic low-VOC options.

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

Paper Underlayments Used Under Wood Floors

Silicone Paper

Silicone paper is usually used under real solid hardwood floors, but it can also be used under engineered wood. It is semi-permeable which is good, as you want your upper floors (over wood subfloors) to be breathable in almost all situations.

It meets perm ratings recommended by the National Wood Flooring Association.

Those extremely sensitive to chemicals have liked this product a lot. If you just need something simple that is not providing sound dampening or leveling this will do the job.

Red Rosin Paper

Tried a true, Red Rosin is the old school underlayment paper used under real wood flooring. It’s extremely low in odor and even that dissipates rather quickly. The extremely sensitive almost always do well with this, with only a few people mentioning that the undyed Rosin Paper was preferred.

This is what I would use under wood floors. Keep it simple and breathable.

Foam Underlayments for Click Together Floors

Basic Polyethylene Foam

For laminate, engineered and other click-together floating floors I prefer the most basic polyethylene underlayment. It’s very simple – it’s one of the safest plastics in terms of odors and offgassing (it’s zero-VOC).

This provides some cushioning which is necessary under flooring types like laminate.

It’s not a complete vapor barrier, so it can breathe, which is great for upper-level floors. Plus, it’s very inexpensive.

This is the type of foam that comes pre-attached in some laminate lines. I find that very convenient.

A “2 in 1” will usually have polyethylene foam and a thin layer of plastic. If you are looking for a vapor barrier, make sure it has one attached. The term 2 in 1 is rather confusing in this sense, as some are moisture-resistant and some have vapor barriers, but they are very thin.

Check with the flooring company and your contractor to make sure you have an appropriate vapor barrier, if one is required.

Cali Bamboo brand makes a good polyethylene underlay with foil as the vapor barrier, made for their floating floors. And Kahrs makes a polyethylene foam with 3 mil poly plastic for their engineered floors.

Some are just the foam, which is the type I would use over wood subfloors.

Polypropylene Foam

Polypropylene foam is another very safe plastic. It’s not as breathable as polyethylene and I have only seen it advertised as being a vapor barrier or as having a vapor barrier (another plastic layer) attached to it.

It’s used for laminate and engineered (mostly) when a vapor barrier is required. It can be used under solid hardwood floors to provide cushioning and sound dampening.

If it’s labeled 3 in 1 that usually means it’s cushioning, sound dampening, and a vapor barrier.

Floor Muffler has not tested their products with carpet. Their polypropylene underlayment is free of any added flame retardants.

They have a high acoustical rating, the one below can meet IIC up to (74) dB per ASTM E 492 / ASTM E 989, STC up to (73) dB per ASTM E 90. Mohawk Silent Guard is STC 73, IIC 71.

EVA Foam

EVA foam is another safe foam. Compared to polypropylene and polyethylene it does have slightly more of an odor.

EVA foam underlayment can be used under floating floors like engineered wood, laminate, bamboo, and vinyl as well as carpet.

IIC (Impact Sound Transmission Test) rating is 73, STC (Sound Transmission Class) is 72.

Felt Underlayment For Engineered Floors

Felt + Vapour Barrier

Quietwalk is felt and a vapor barrier made for under laminate and engineered wood as well as other floating floors like bamboo and luxury vinyl plank.

The felt and (polyethylene) plastic layers are quite safe even for the chemically sensitive. It claims to be zero-VOC.

This one does contain Microban (Microban can refer to hundreds of chemicals, so this could be anything from silver to something more synthetic). If you want it without antimicrobials you can get Quietwalk from Green Building Supply.

Because this has a vapor barrier it’s meant for on top of a slab or basement floor. If you do lay down laminate, engineered, or another organic-based click-together floor on a slab or basement you do need a vapor barrier.

Best practice, according to mold preventative architects, is not to apply flooring that requires a vapor barrier over a slab because a concrete floor is always trying to dry to the inside. As a mold-sensitive person, I can smell the mold that festers underneath when a vapor barrier is applied. And it happens in most homes in my experience.

Available on Amazon or Walmart.

Natural Material Underlayment For Many Floor Types

Breathable Cork

Cork underlayment is one of the most expensive underlayments. It provides good cushioning and sound dampening as well as some leveling.

It can be used under engineered hardwood, laminate floors, hardwood flooring, and ceramic tiles.

The small pieces of cork are usually pressed together with a polyurethane glue which I find to be quite strong in offgassing, so I don’t personally use this underlayment. However some brands are made with polyethylene as the binder, which is much much better in terms of odor and offgassing. Eco Cork Foam, says they use polyethylene as the main binder.

They also recommended to glue the underlayment down.

There are many flooring types and brands that come with an already attached cork underlayment, which also always has this polyurethane offgassing odor.

1/2”(12mm) cork underlayment has STC 49 and IIC 48 sound ratings.

Cork with a Vapour Barrier

Eco Cork Foam is not as natural as the pure cork above. This version combines cork with polyethylene foam and a 6 mil poly vapor barrier.

Pressed Wood Underlayment

This Steico product is a lot more unusual than the others. This is different from the old particle board underlayments. They claim it is more water-resistant than particleboard.

It’s a pressed wood product, but they don’t mention what kind of wax, oil, or glue is used to make it. They do claim it is zero-VOC.

It can be used under floating floors like LVT, laminate, and engineered wood, as well as hardwood floors.

It seems to be very good at sound dampening.

Available on Amazon or Walmart.

Vapor Barrier for Over a Slab or Basement Floor

6 Mil Poly

This is the most common vapor barrier for slabs and basements. If I was going to put down a vapor barrier (which I wouldn’t due to the reasons discussed above) I would go with plain 6 mil polyethylene plastic. There is no need for anything fancy here. Though it does not provide cushioning. If cushioning is required it makes sense to buy a foam and vapor barrier in one. I would make sure it’s 6 mil though.

Flooring with Attached Underlayment

Many click-together floors come with an attached underlayment. This really helps in simplifying things.

I like laminate floors with polyethylene foam backing attached, LVP with rubber underlayment attached, and engineered flooring with cork already attached.

Luxury Vinyl Plank (LVP) with a cork backing does not make sense to me in a basement, slab or wet area since one of the main benefits to LVP is that it is waterproof and very mold resistant.

Some LVP comes with a EVA underlayment.

Underlayment for Tile

I like the Schluter system under tile.

If you need zero-VOC acoustical control under tile Schluter DITRA-HEAT-DUO providers a ΔIIC contribution of 20. Cork underlayment can also be used under tile.

Many acoustical underlayments for tiles are rubber-based, and I would personally avoid those as they are one of the highest offgassing products in a home. (Whisper mat is one that is mostly foam with some asphalt adhesive, so that would be an improvement over most rubber underlays).

Laticrete Fracture Ban is not toxin-free but it’s one I have seen that is breathable. LL Floors Fiber Fusion Anti-Fracture Crack Isolation Membrane might also be breathable.

They have different membranes that I discuss more in the grout and thinset post.

They are made of a non-toxic very low odor plastic that even chemically sensitive folks do well with.

Photo Schulter membrane from Amazon.

Underlayment for Carpet

The main healthy options are natural wool felt for wool carpet, polyethylene, EVA foam, low-odor synthetic rubber, or built-in synthetic felt.

My carpet post goes into detail on underlayment for carpet.

Corinne Segura is a Building Biologist Practitioner with 8 years of experience helping others create healthy homes.

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Filed Under: Healthy Building, Healthy Interiors Tagged With: Healthy building, healthy interiors, mold prevention

17 Non-Toxic Eco Prefab Homes Compared

February 4, 2020 by Corinne 27 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 closer inspection.

When considering a prefab, it’s important to see the detailed 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 a 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.

This post focuses on standard size homes. If you are looking for smaller and more affordable homes, my post on small and simple homes covers those.

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

  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. 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 of 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 down 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

If You Have Chemical Sensitivities

  • Another thing I look for is to make sure we have control over the finishes in a way that suits your environmental sensitivities.
  • 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.
  • 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.

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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 the 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.

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.

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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 demonstrate “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 on 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 prototypes. 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.

Corinne Segura is a Building Biologist Practitioner with 8 years of experience helping others create healthy homes.

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

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Filed Under: Healthy Building, Mold-Free Building Tagged With: Healthy building, mold prevention, tiny homes and trailers

Designed for Mold-Prevention – Corbett’s Tiny House

January 15, 2020 by Corinne 3 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 Practitioner with 8 years of experience helping others create healthy homes.

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

Get Rid of Mold in Your Car, Including AC System

January 8, 2020 by Corinne 9 Comments

prevent and treat mold in vehicles

This article covers the sources of mold growth in vehicles – AC system, high humidity storage, spills, leaks, and design malfunctions – and how to prevent them.

I go into detail on the four methods used to clean the HVAC system out, as well as methods to clean mold and cross-contamination in the vehicle as a whole.

The AC is usually the most difficult area in the vehicle to manage microbial growth. While there are certain makes and models of vehicles where this is more of an issue, to some degree it’s a problem in all vehicles due to the inherent design of the AC system.

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

Preventing Mold in Vehicles

Preventing Mold in the AC and Heating System (HVAC)

prevent mold in the car's AC system

The fungi and bacteria grow mostly in the evaporator core and immediate surrounds, due to humidity and moisture that forms when AC is in use. Mold can form in the ductwork as well.

To help reduce mold formation in the AC system, run the fan for the last 10 min after using the AC. (Defrost is also AC, so you need to run the fan for 10 minutes after defrost as well). This helps the evaporator dry out.

Using recirculate can worsen the problem in some situations. Bringing in fresh air (if the outdoor air has drier absolute humidity) as opposed to using recirculate can help the evaporator to dry out.

Another thing you can do is to avoid parking in areas where a lot of debris can enter the air intake.

Similarly, when driving through very dusty areas, you are bringing in dust and spores through the air intake. You may want to turn off the HVAC system completely in those conditions.

Maintenence on the vehicle should include changing the cabin air filter as needed (when it’s dirty).

I would include one of the four HVAC cleaning methods below as a preventative (before you start smelling or reacting to mold) if you do use the AC system regularly.

For those Extremely Sensitive to Mold in HVAC – How do you Turn off the AC?

Many folks who are extremely sensitive to mold do not use the AC system in their vehicle at all. If you refrain from using this right from the start with a new car, you will avoid most of the problems here.

If you want to avoid AC use altogether, using just the heating system should be fine. But, keep in mind many new vehicle models have automatic climate control which will use both heating and cooling under many different conditions (not just when defrosting). If you want to turn off the AC, look for a vehicle where this can be done – new cars have a way to disconnect the AC compressor. Ask a mechanic how to do this.

Does the auto setting on cars use AC and how to turn off AC

If you have already used the vehicle’s AC or you bought a used vehicle that has some funk in the HVAC system, then even the heating setting will circulate the fungi and bacteria throughout the vehicle.

Buying a vehicle with heated seats is a good idea in case you become sensitized to the vented HVAC and need to turn it off for a while (and try and clean it). Some very sensitive folks have had to turn it off permanently if they have not had success with the cleaning methods.

One other hack is that you can externally mount the HVAC system to get easy access to the evaporator. This is a very unusual hack. You can find photos of it in the group Mold Avoiders on the Road.

Alternative Ways to Stay Cool in the Car

Cars that Come with Cooling Seats

Some of these built-in systems blow unrefrigerated air through the cushions. And some use refrigerated air that is tied into the main AC systems. The unrefrigerated air system may be safe in terms of mold prevention.

Safer Cooling Seats (or Heating)

You can also add your own cooling and heating seats to avoid the use of your car’s HVAC system.

Cooling seats that you add yourself work simply by adding a fan that blows unconditioned air which helps to cool you down.

Some use fans and those can be affordable. (Though they might be made of vinyl).

The heated seats use coils, just like a heated blanket or heated jacket. Some models do both.

Then there are gel seats, I like the idea of the ones you put in the freezer first, then you bring it out to the car with you. This is a kids version. If you know an adult version let me know, I think it’s a good idea. You will want to dry those off though, when they come out of the freezer they are probably going to condensate.

Cooling Vests

When I used to have severe heat intolerance, I used cooling vests on my body – both active and passive vests work.

The active vests provide more cooling but are more expensive.

They were life-saving for me until I healed from heat intolerance.

Preventing Mold in the Car (as a Whole)

does mold grow in cars just from sitting in humid climates
Many of us stored our vehicles in the humid winters of the Pacific Northwest, to come back to moldy cars

Why Mold Grows Inside Vehicles

There are a few ways your vehicle can become moldy inside on the seats and upholstery. Sometimes just leaving a car to sit in a very humid place for long periods of time can cause mold to start growing on the seats.

More common though, is a spill or window left open that wasn’t dealt with fast enough.

Other sources of water damage are less common:

  • Debris accumulating in the air intake areas and connected drains (keep your air intake area clean, and change the filter). The cowl intake and drain area can collect debris. Those areas are connected to body cavities that can harbor microbial growth. Thus structural mold is possible in a vehicle, though this is less likely than mold growth in the HVAC and inside the vehicle.
  • Rainwater that has gotten into the HVAC ducts and car interior in some past Ford models – causing hidden pooling of water.

Ways to Prevent Mold Growth in Vehicles

Prevention here is key. Once mold is actively growing and has made it through to the foam in the seats, it’s a huge problem that is hard to fix.

When storing your vehicle for long periods of time in a constantly humid climate, it’s best to leave it in a sunny spot and leave it with a dehumidifier. Climate-controlled indoor storage is of course ideal.

Though generally, a vehicle should be able to withstand a good amount of humidity while being stored, really high humidity for long periods has been a problem. I left a truck in 70-95% humidity for a couple of months and came back to mold growth. No known water intrusion.

Many others in the Pacific North West or in semi-tropical and tropical areas have left vehicles sitting to come back to visible mold growing (and not from leaks).

Both active (electricity-powered), and passive dehumidifiers will help. You can also monitor the outdoor humidity.

I would check on the vehicle (or have someone check on it), both to empty the dehumidifiers and possibly to dry the vehicle out actively with heat and airing every few days if necessary.

When you spill something or leave the window open, just do everything you can to dry it out within a day, which includes the above: usually sun and air, or heat and air. Add dehumidification only if it’s going too slowly.

Decon/Clean Mold or Cross-Contamination in a Car

DISCLAIMER: Some of the cleaning methods discussed in this article, which include ozone, chlorine dioxide, hydrogen peroxide, and quaternary ammonia, require knowledge of safety precautions for handling the materials, and executing these methods. Please take full responsibility for your health and wellbeing and make sure you understand the risks, precautions, and procedures – not all of which are explained here in full (please research them before proceeding or consult with an expert). Full disclaimer here.

use a HEPA vacuum to decon mold in a car

If you do have some light surface mold in the car or cross-contamination, I would start with a deep clean.

If you had a big spill that didn’t dry out, or you suspect someone else did in your vehicle, you might want to open the seat covers to check on the foam. Some have zippers. If they don’t you would have to cut them open to check.

Mold in the foam cannot be properly remediated other than with replacement.

Deep Clean your Vehicle

You can remove light surface mold or cross-contamination by steam cleaning or shampooing the seats.

Make sure it is dried out quickly after that. Car detailing shops can do this. Just make sure you know which products they are using, as some might not be acceptable, toxin-wise.

A mechanic I talked to near Vancouver BC, does a shampoo of the seats with high temp extraction, then an enzyme spray on the seats instead of ozone to reduce odors. I use natural enzymes to break down odors.

DIY HEPA Sandwich for a Car

If it’s not so bad as to warrant a steam clean or extractor shampoo, use a HEPA vacuum, which you can do yourself. Vacuum the seats, carpet, and upholstery.

For a vehicle, you want a rather flexible hose. I would use a shop vac. I’ve used one before with the HEPA filter and HEPA filter bags.

You can then wipe down all surfaces with quats or the cleaning product of your choice. A proper “HEPA sandwich” clean would involve another round of vacuuming.

Having your car or truck professionally detailed can help, as they do a very thorough clean, though I haven’t seen them do HEPA vacuuming.

Using Ozone on Cross Contamination

If those methods don’t cut it, and you are still sensing mold in the vehicle, you will want to use the methods below.

Many people do use ozone and it does work, but it leaves behind oxidation, which smells quite terrible.

Depending on how long you ozonated it for, it can take a while to die down.

I don’t agree with some who say that you will damage the wiring easily, you would have to use extremely high levels for a very long time to do damage like that.

Many mold-sensitive folks have ozonated vehicles at very high concentrations for 24 hours, many times. I have done a couple of 24-hour treatments on my truck.

Car dealerships use this all the time as well (but normally in much shorter treatments, like 1 hour). Many people only do 2-hour treatments for mold, which should not cause damage to the plastics, and would only cause minimal oxidation odor after.

There is more info below on pumping ozone through the HVAC. If you don’t need to pump it through the HVAC, just see my general post on ozone and run it inside the vehicle. I use many of the little ones from Amazon (like this one).

Please read through the precautions thoroughly, since ozone is a dangerous gas that can be deadly.

Another oxidization method, though it is a weaker oxidizer than ozone, is to use chlorine dioxide gas. That method is explained below, in its own section.

Other Fogging Methods for Mold

If you have another decon method that has worked well for you in decontaminating your house from mold, it’s likely you can use that here – like thieves oil fogging, Concrobium fogging, or using quats.

Silver Hydrogen Peroxide though, is likely too much oxidation for most vehicles, though it can be used in the empty part of metal cargo vans.

Chlorine Dioxide Gas to Treat Mold

Chlorine Dioxide, like ozone is an oxidizer. Like ozone, there is evidence that it breaks down mold and mycotoxins.

Although it’s weaker than ozone, you should take the same safety precautions outlined here. It is dangerous to breathe in and it’s explosive in certain concentrations.

You may not need to be so far away from it like with high doses of ozone, which is an upside. It’s also cheaper and easier.

Keep it simple and buy the ready-made tablets or packets on Amazon. They are inexpensive and work just as well as mixing it yourself. NosGuard is one brand, Reset is another one.

Read the safety instructions carefully on the product and make sure you understand them. Never use a chlorine dioxide product in occupied spaces.

If you want to make it yourself, please take full responsibility for your safety and wellbeing. Here are the instructions:

How to make chlorine dioxide gas treatment for the home or car: 6.5 oz (roughly 3/4 cup) Oxine plus 3-4 tsp citric acid in glass or heavy plastic container, one for each room. Leave it for 3 hours for a shock treatment or 24 hours for a deep treatment.

You can make a smaller batch for smaller spaces with the same ratio. It takes about a minute for the reaction to take place, the liquid will turn yellow, and for about 3 hours it will release chlorine dioxide as a gas. Take similar precautions as with ozone for airing it out and re-entering.

Four Methods for Cleaning Mold from the AC (HVAC) System of the Car

1. Take it to a Dealership – Have them Clean out the System

Skill Level – Easy. Results – Can work, depending on which methods they use.

how to clean mold out of the AC system of a car

There are a number of different cleaning methods used by automotive repair shops to clean out the AC system. Some use ozone and even run it through the HVAC in the same way as described in the next section on ozone.

There are also treatments that are similar to #4 on this list, introducing a product into the system to clean the evaporator.

One mechanic explains: “one is a mist treatment, using a product which foams up. You drill a hole in the case and then introduce the mist to the evaporator core and let it sit, give it time to work, and then flush it out.” (source).

Some of these might have fragrance of other toxic additives but others would be acceptable for many folks who are sensitive to chemicals.

2. Using Ozone Through the HVAC

Skill Level – Intermediate. Results – works on most mold and bacteria.

how to use ozone to clean out a car or AC system

This is a technique used by some car detailers and dealerships and mold-sensitive folks.

The simplest way to do it is to run an ozone machine in the car while the vehicle is running so that the ozone is pulled in through the air intake. Most people would run this through for a couple of hours. Depending on the amount of ozone and the time you run it for, you may need a window open to provide oxygen.

If you are running the machine in the car I would use a small machine like the ones on Amazon for under 100$.

Instead of running the vehicle, you could alternatively, hook up the battery to a battery charger to run through the HVAC settings that way.

For any serious contamination or if you want to blast this more directly through the HVAC, mold avoiders tend to use an external ozone machine that pumps in the gas, giving the machine full access to oxygen outside. Bioblaster is the most popular one.

If you are in the Facebook group Mold Avoiders, you will be able to see an example of a Bioblaster hooked up right to the air intake here.

That machine is overkill for me. But others may need this. I would have no problem running the smaller ones on Amazon that I have used many times and pumping those through the HVAC system with tubing from the outside.

To get it through all the different parts of the HVAC system, the ozone needs to run through it on all settings (heat, AC, recirculate). Run it through each setting for at least 20 min. The next section explains more about how to access the air intake.

This is tricky because of how far away you need to be from the ozone. Let it air out each time before coming close enough to the vehicle to change the settings. Again, ozone precautions are here.

3. Spray Through the Air Intakes

Skill Level – Beginner to Intermediate. Results – May or may not work.

spray in the air intake to kill mold in a car
The air intake is usually right under the front windshield

In this method, hydrogen peroxide or quats are sprayed through the air intake.

Some very mold-sensitive folks have had success with 10% hydrogen peroxide sprayed into the air intake with these video instructions (not with toxic products like scented Lysol). Seeing the process in a video really helps to make sense of it.  

Spray the hydrogen peroxide through each setting for 3 min. You can use this mister.

You will be using 29, 30 or 35% peroxide (depending on what you can source) and diluting it down to 10% (here is the dilution table). Please research and take full responsibility for handling and spraying this concentration of hydrogen peroxide.

Some people found this worked better with quats (a type of ammonia). This ACDelco product was recommended.

4. Greg Muske’s Quats Cleaning Strategy

Skill Level – Very Advanced. Results – Likely to work if you do it right.

how to clean the evaporator core
From http://biotoxinjourney.com/clean-driving-machine/

Greg Muske from Biotoxin Journey has a detailed and more complex method of accessing the entire HVAC system and runnings quats (i.e. quaternary ammonium) through it.

You need some mechanical expertise for this method as it does involve drilling into specific parts of the system, which differ depending on your make and model.

You need someone who can understand the heater core diagram for your car, which you can look up online. You’re going to locate the evaporator core. Then drench the two cores by running about one gallon of quats solution into 3 access holes. Followed by a water rinse.

Greg also misted quats through the ductwork via the vents and the opening for the cabin filter directly above the blower (after removing the filter), and air inlet holes located under the hood next to the firewall. Unlike when cleaning the cores, this was not rinsed out. It was dried out by running the heater and fan on high.

Greg then cleaned out the rest of the car by using a steam cleaner on the carpet with Thieves Oil Cleaner. (You can use the cleaner of your choice). All other surfaces in the vehicle were wiped down with quats.

Full instructions and a video can be found here: Clean Driving Machine. This section was printed with permission from Greg Muske.

Corinne Segura is a Building Biologist Practitioner with 8 years of experience helping others create healthy homes.

This post was written with input from two engineers, a mechanic, and a car detailer.

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 Avoidance Paradigm, Mold-Free Interiors, Tiny Homes and Trailers Tagged With: mold avoidance paradigm, mold prevention, vehicles

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Hi, I’m Corinne Segura, I hold a certificate in Building Biology, and a certificate in Healthier Materials and Sustainable Buildings, among other credentials below. I have 8 years of experience helping people create healthy homes.

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