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

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

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

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

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

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

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

Steps to Building a Healthy Prefab

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

Good Signs and Red Flags

• The age of the company is important to me. They should not be on their first prototypes. Ideally, you should be able to see some of their houses that are at least 10 years old. You should feel confident in the person running the company. They need to be in business (in the future) to honor warranties. There are two good companies, however, on this list that are less than 10 years old (Ecocor and GO Logic).

• A company without architects or building science experts on the team needs to be looked at more carefully. Who is in charge of the design and how knowledgeable are the project managers? Steer clear of any company that doesn’t promote their building science expertise.

• If the company provides the General Contractor or works with a network of general contractors, vet them just as carefully. If you don’t have enough choice in who you use to build it out on-site, you won’t get a well-built house.

• While you should expect to make minor changes to the design with your architect as a consultant on the team, any major design flaws in their models is a red flag.

• Talk to someone who built with the company recently. If the company is disorganized and the project manager could not coordinate all teams well, that’s going to be a huge mess. Things might not get done right due to this problem (which is a common one with prefabs).

• I look for the ability to tour the factory—ideally the company owns the factory—and make sure you see a house that is built. Even better if it’s a hotel or Airbnb you can stay in.

• You need to be able to see details of the building systems/designs system before committing any substantial amount of money.

Pros and Cons of Building Prefab

Benefits to Building Prefab

• Mistakes are limited in the really good factories—computer planning, precise cuts, fabrication by machines, and panels put together by highly trained technicians limit mistakes that are extremely common in traditional builds.

• Build out of the rain—the wood and other components are stored inside and stay dry (in theory, if it’s a good company). The panels or modules will be built in a climate-controlled factory. It goes up faster on-site, during a dry time, and should be watertight before it rains.

• Enjoy cost savings—it would be very expensive to build a house at as high of a quality as some on these on this list from scratch, with high-quality craftmanship like that accomplished in the factory. If you go with a predesigned layout (not custom), prefab helps you save even more. With many companies, you may also have a more fixed price than in a conventional build where many things tend to change.

• It’s faster—the whole process from start to finish is likely to be faster than with a conventional build.

• There’s less work for you — while you do have to tour the factory and have the plans reviewed by an architect, you don’t have to supervise as many parts as in a conventional build. Wall and roof panels, and in some cases whole modules, will all be done in the factory setting and, if the factory is good, it’s likely to be done very precisely and correctly. That is almost never the case on-site at a conventional build. Since most homeowners don’t have the knowledge to supervise a build, this can be essential.

Downsides to Building Prefab

• Have less control—while it might be possible to be in the factory during the manufacturing of your specific panels, you don’t have full control here over supervision in the same way you would on-site.

• If you are extremely sensitive, you need to have confidence in the factory that they are only using clean wood, stored correctly, etc. (The same goes for all the components, but with the wall systems the wood is clearly the most important part).

• Ability to analyze and review/change the plans—with some companies, you cannot see the full details of the plans (or the walls, ceiling, floor system) until you put a deposit. This is a huge problem. The good companies do show their designs.

• Some companies will not allow you to bring your own architect as a consultant on the plans (though most will). That would be a deal-breaker for me.

• Supervision is still needed—assuming you were able to have your plans reviewed by multiple experts, and feel confident in the factory making the panels or prefab, you still have a fair amount of planning and supervising on-site, making sure the local team knows how to put this together properly, that the foundation is detailed right, the land was prepared properly, and the final on-site details (like the roof) are done right.

• On the topic of supervision, if the prefab is a very unusual system, it becomes more difficult to have it confidently reviewed and to supervise it.

• Possible lack of coordination between teams—with some companies that don’t have a strong process in place and strong project managers, and/or if your builder is not on board from the start, you may have a lot of difficulties arising between the parties, with no clear person/company responsible when things go wrong.

• Prefabs aren’t typically inspected in the usual way—they are inspected in sections, and the companies have individual agreements with the states to allow them to do “inspections” out of state and/or off-site. When the local inspector checks in order to give you a certificate of occupancy, they are only checking things at the finished level, not the construction level.

Building with Environmental Sensitivities

If You Have Chemical Sensitivities

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

If You Have Mold Sensitivities

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

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

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

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

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

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

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

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

Materials and Design

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

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

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

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

Moisture-management

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

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

They use mechanical ventilation (HRV).

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

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

Here is a video tour about the company.

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

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

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

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

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

4. Morton Metal Siding Structure

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

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

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

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

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

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

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

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

Materials

Zip panels with cellulose insulation.

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

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

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

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

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

How long have they been in business? Since 2017.

You can see a video of their first house here:

9. Haus.me

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

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

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

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

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

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

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

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 

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.

Those that Didn’t Make the List

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

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

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

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

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

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

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

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

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

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

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

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

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

Concluding Thoughts

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

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

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

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

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

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

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

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

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

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

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