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Simple, Small Modular and Custom Homes for those Sensitive to Mold and Chemicals
These are small and tiny houses (not on wheels) that are suitable for those with extreme sensitivities to mold and or chemicals.
Not all materials will work for all folks, that is why this article features everything from all wood, to all plastic and all metal homes.
I have natural materials on the list as well, like hemp and concrete.
These small houses are ideal to create a healing space away from conventional housing that is so prone to problems.
This post contains an affiliate link to a home sold on Amazon. This home was on this list before they starting selling through Amazon. Upon purchase, through affiliate links I earn a commission at no extra cost to you. This post is not otherwise sponsored by any of the companies.
1. Passive Home Tiny Homes
Besonwood is a high-quality passive home custom prefab company. Their custom Thoreau Cabin home is 150 sq ft. The owner chose the stone facade but that is not a typical facade. They are custom homes so they can build any size.
Their predesigned wing is called Unity Homes. Their smallest house “Nano” is 477 sq ft.
They are wood framed with passive house design, made to high standards. This would not work for those extremely sensitive to offgassing as their walls include OSB and engineered wood framing.
The insulation used is Rockwool and cellulose in the model I saw (they have different wall systems to choose from).
This is a house that mold sensitive folks should consider due to their high-quality design, high-quality factory-built, and indoor factory conditions. This is at the top of my list for a reason, I would build with this company.
You still have to have planning and supervision on the site prep, foundation and the installation of the prefab components. Every detail matters for mold prevention.
2. All Wood Prefab
Photo Here: https://www.instagram.com/p/B0WFlacAU-2/
The Holz100 homes come in all sizes from very very tiny, small and large.
The walls, floor and ceiling are all wood, no glue, no nails. The roof will not be all wood, there will need to be another roofing material there.
I have a more in depth review in the general prefab post.
I think this house is very promising but needs more investigation. If you tolerate wood there is nothing else in the interior.
To hit codes you will need to put exterior insulation on it. Exterior foam insulation would also be a fool safe method to prevent possible condensation within the air pockets of the wood wall. That is how I would detail it for mold prevention. This would make it quite pricey.
3. Wooden Treehouse
From Out N’ About, a company that rents out treehouses, sells plans and parts, this 16′ Treezebo Hexagon could be a great non-toxic home.
The plans for the treehouse includes a 3-hour consultation.
I like this simple option if you don’t need insulation. Using a rot-resistant wood and no need to worry about the foundation type simplifies everything here.
This can be a mold preventative option.
4. Arched Cabins
The basic kit for Arched Cabins includes floor plates, ribs, ridge beam, standard R13 insulation, Super Span Roof Paneling, trim, and fasteners needed to assemble the cabin.
Arched Cabin kits do not include the foundation, installation, interior, end caps, delivery.
What I like about arched cabins is that there could never be any leaks with this one-piece roof/siding.
In this design, you can use spray foam insulation (with or without rigid foam) without worrying about exterior leaks getting in behind. Spray foam, while it does offgas, is a vapor barrier and the best bet for insulating metal walls in heating climates. It’s risky though to use anything with an exterior vapor barrier (no rain screen) in a heating climate. Spray foam could pull away from the skin. Plus spray foam off gasses too much for chemically sensitive folks.
Either closed cell (2 part) spray foam is used to form an airtight vapor barrier in any climate where you heat, or not quite as foolproof is rigid insulation installed with canned (1 part) spray foam).
This could work for preventing mold, but I don’t think anything with a metal exterior is a good idea in heating climates, it’s far too dependent on spray foam holding up perfectly or a plastic barrier holding up perfectly. I would not risk that myself. And I would not use anything with an exterior metal or fibreglass vapor barrier in a heating climate myself.
The large overhangs are also superb protection from rain over the windows and doors on the ends.
The 12×12 kit is $2400. This is a simple, mostly metal kit that you could then customize to be chemical-free on the inside.
5. Plastic Domes
These cool Intershelter domes are easy to transport and assemble and have a lifespan of 30 years.
The larger domes are made of a fiberglass composite material that the company says does not emit an odor. Some sensitive people say fiberglass needs some time to offgas (1-2 years or more) and others find it OK fairly soon after production.
The small domes are 14 feet and are made of ABS plastic, which is a really safe plastic (the same plastic the LEGO is made of). This one they say has an integrated foam component.
I would look closely at the details on the panels that have integrated foam. You would want to make sure this is not likely to leak.
If this is done well this would be much easier than trying to put foam insulation on the inside of the one-panel fiberglass domes yourself.
The integrated foam would be ideal for heating climates (cold climates).
Installing foam in the larger domes with an exterior vapor barrier is not simple in heating climate. If you are in a tropical climate this might be ideal.
6. Plastic “Lego” Home
EverBlock makes plastic blocks that fit together like lego. You can make a simple structure out of these.
It’s a safer plastic than fiberglass that is much more tolerable for the chemically sensitive.
7. Plastic Module Homes
There are a few designs that are using metal framing with a plastic body. I find this design extremely promising.
The Coodo above is made in Germany and can deliver all around the world.
The downside is that fiberglass does offgas and won’t work for many sensitive folks, at least not right away.
Both have the potential to be very waterproof and mold-resistant designs. Neither one gives too much away on how it’s built exactly, so we cannot evaluate it in great detail.
Just like when looking at larger prefabs you have to go through the reconnaissance process outlined here.
Another similar model is the Haus.me which I go into more detail on in the prefab article. This one looks to be a different type of plastic, not fiberglass, though they don’t say which type. They claim that it doesn’t offgas.
Photos here: https://www.instagram.com/p/B1916GAIsFr/
8. Log Cabins
For a thicker wood wall look at a company like Montana Mobile Cabins. This true round log cabin does not use insulation.
I much prefer this simple design than to try and insulate a wood-framed cabin. This is a much safer bet for mold prevention.
It’s not perfect as I have heard of condensation in log cabins, I would consult with a building science expert on how to make this work in your climate.
Prefab Square Log Cabins
Photo here: https://www.instagram.com/p/BJi5A7SgtDQ/
I like the thick square logs too. I like that they would fit together well. In theory, this might create a more airtight assembly which might help prevent moisture and condensation issues.
Confederation Log Homes above makes custom prefab log homes with square-cut logs. The company has been around for a long time.
This is the first log home company I would look at due to their extensive experience.
9. A Metal SIPS House
The Nomad Cube
The Nomad Cube is a promising little metal SIPs house. It can be built out to be very non-toxic.
Metal SIPs make up the main walls and roof of the house and are made from laminated steel-EPS white styrofoam-steel. They are essentially 0-VOC and extremely resistant to mold as long as the panels stay laminated together and assuming there are no leaks into the panels.
The smaller Nomad Micro has been redesigned since I originally wrote this. That one is no longer a SIPS house. Also be sure to ask about and eliminate wood in the structure.
The Nomad Cube is 13 x 13.
You need to add: shipping (From Vancouver BC), platform/slab/or piers, installation, wiring, heat, plumbing, hot water heater, roofing membrane, interior walls, baseboards, shower door, ladder/stairs, fridge, range, and hood vent.
My most sensitive friend tested the SIPs and thought they were good. It is possible to complete the interior with non-toxic materials.
The basic design of this house is metal framing with metal SIPs. It appears in one of their videos that there is plywood in the base, which I would change.
You will need to have a building science expert review this design and help with the details along the way.
I consider this one of the most promising designs here. It’s the first option on this list I would look into for something really small and simple.
Metal SIPS homes work really well for mold and chemical sensitivities.
Make Your Own SIPS House
These are also metal-EPS foam-metal and have an internal locking together system that allows them to quickly snap together.
In this design the panels are fully structural elements, there is no additional metal framing. The panels make up the walls and roof.
To create a long-term structure you would use siding on top of the SIPS and pour a cement slab to the same standards that you would use on a house.
But quick and dirty, you can throw up these panels fast and get away without siding if you don’t need it to last forever.
This is the fastest and safest (for both mold and chemical sensitivity) option on the list.
Art Span Inc
While I have no problems with the two above, I really like this Canadian company Art Span that makes SIP panels. It can be difficult to source the panels from the companies above and this one is easier to buy from.
They also have a couple of simple designs that are already kits. I like the little ice shack as well as the little houses.
I have a friend that built one and liked it and here is a full post about this with cost breakdown and photos.
Review of Boxabl SIPS House
The company Boxabl has created a metal SIPs 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.
First, is it good for chemically sensitive folks?
Yes, the basic structure of steel/foam SIPs is very safe for those with chemical sensitivities. That part has practically no offgassing.
They also use MgO board on the interior surfaces which is generally safe for most people with MCS. It’s not clear how that is attached, it’s likely glued on, which could be a problem for offgassing.
The flooring appears to be glue down vinyl, though they have described it in different ways. The countertops and tabletop are laminate. And the interior cabinetry is conventional. These three elements will contribute to offgassing of some VOCs, plasticizers, glues, and formaldehyde.
Is it a mold preventative design?
In general, metal SIPS are very resistant to mold because as long as the wall remains laminated they are immune to condensation problems. The waterproofing will depend on how well the seams are connected.
There are a number of concerns I have with this house:
- There is a clear negative lap at the bottom of the first piece. It’s not just an exterior trim detail, it’s integral to the design. I don’t see how you would not always be battling water pooling up and soaking the wall.
- It’s nice that it unpacks quickly into a full livable house but how are all those seams waterproofed? I do not think we have enough information on that right now.
- Because it’s done almost entirely in a factory we would need to see a detailed factory tour to see if this is a good design. There are so many details I would want to see including how the windows and all seams are waterproofed.
- The house, like all prefabs, needs to be seen in person, especially during installation to see if there are any vulnerable to water areas.
- MgO and steel have not gone well together in the past. In Denmark, massive problems were caused when salts naturally leached out of MgO and corroded the metal in the buildings.
- The website says that Boxabl “doesn’t use lumber or sheetrock” and in an email they said “we do not use wood or materials that can rot or mold”. But in multiple videos, wood appears to be the framing of the edges of the SIPs. Hidden wood in a metal-based house is a problem in my books.
For more thoughts on this prefab I have a post on this company.
Ecosteel homes are made of metal-foam SIPs, but this company uses polyurethane which usually has a little bit of offgassing (from the foam, blocked by the metal but it could come through at the seams).
They have a one bedroom that is already designed. It’s 165K which only includes plans and panels.
10. Hemp House
Hemp House Pods – a simple 8 x 12 structure meant to qualify as an ADU (without a permit) is made from hemp and a wood frame. Hemp may be mold resistant in certain climates. I would likely only use this in dry climates. My post on Hempcrete has more info.
I would have this reviewed just like all the others. I would use huge overhangs and I would look more closely at a foundation type that does not wick moisture up.
The cost does not include plumbing, electrical, or the deck.
They say they go up in a week.
11. Concrete AirCrete Dome
I reviewed the AirCrete dome for mold resilience and I have a few thoughts on it. (Note this is different from AirKrete with a “K” insulation, though it’s a very similar material).
AirCrete domes are made of a mix of concrete and a foaming agent. You can use a natural dish soap like 7th Generation.
They were originally used in tropical settings and I do think they might this is simpler in climates that don’t require heating.
Mold Preventative Design of the Roofs
I do not like any of the designs that have multiple domes coming together creating valleys where water will not drain well. In some designs, debris is even accumulating in those valleys. I would only do single domes with as steep of a slope as possible.
No valleys where water and debris collect and soaks in. This is always best practice for mold prevention in houses.
The steeper the slope the better it will shed water.
The Challenge of the Exterior Coating Creating a Vapour Barrier
The exterior is coated with waterproof exterior stucco and then acrylic or similar concrete sealer.
The coating would have to be waterproof which creates a dilemma in heating climates.
If it’s waterproof then it is usually an exterior vapor barrier, which can cause condensation and mold in climates where heating is used. This is fine to use in climates where only cooling is used.
I might put this whole structure under a second roof, like a carport (or a souped-up metal roof like this house has). That way you don’t have the conflict of the need for a waterproof but also breathable sealant on the exterior of the dome.
You may also consider a sealer that sheds water but is breathable – a layer of concrete stucco sealed with sodium silicate might work. Just like polished concrete which is vapor breathable but should shed water. Consult with a building science expert to work this out.
Can Concrete go Moldy?
Conventional wisdom is that concrete cannot mold because it’s not organic. As a mold-sensitive person, I would say every basement, most slabs, and almost every concrete building in the tropics shows otherwise.
Mold can grow in anything porous, I have found.
Slab Must be Detailed Right for Mold Prevention
It’s also incredibly important to detail the slab right for mold prevention. Slabs are very prone to going moldy in all climates and are rarely detailed properly.
Because slabs are made of concrete and the dome is concrete you also have to take extra precautions with the slab and site details to not have wicking up of water from the ground up through the structure. This could easily happen in rainy climates.
The final flooring over any slab also needs to remain breathable to the inside in best practices for mold prevention. If the slab does take on water through wicking or through water coming in through the sides it needs to dry up.
Only polished concrete, tile (including stone tile), or earthen clay floors should be used as the final floor.
Does the AirCrete Dome Work for Extreme Chemical Sensitivity?
I think this dome would work for many people with MCS.
Admixtures are used in the concrete, you would want to check those out.
The foaming agent can be a non-toxic soap if you tolerate one of those.
The interior can be finished with natural plaster which does not contain additives.
The exterior finish needs to be looked at carefully, synthetic stucco might not work for everyone who is chemically sensitive. That won’t work in most heating climates anyway. Sodium silicate is considered safe for the chemically sensitive.
The slab would have the same concerns as all slabs. You don’t have to use rigid foam in the slab in many climates, but you do need a thick vapor barrier like Stego. It needs gravel underneath and proper grading.
A polished concrete or tile floor works well for chemical sensitivities.
You can find the workshops and the tools needed to create the concrete foam mix at DomGaia.
12. Container Homes
I have not been a fan of container homes in the past because the exterior metal envelope creates a really tricky situation for condensation in every heating climate.
More on that below, but if you are somewhere where you only use AC or no heat or AC this can be just fine.
When I saw that a company is making exterior insulation for shipping containers this changed my mind on the topic. The foam contours to the container and insulating it on the exterior eliminates the condensation issue.
You will still have to detail around the window and doors, and make the steel envelope airtight (I would try to weld all seams) but I really like this idea.
A Note on Exterior Metal and Fiberglass Shells and Mold Prevention
A prefab house that has a metal or fiberglass shell that does not have a rainscreen system is extremely difficult to insulate in most climates where houses are heated. This includes container homes.
“In a cold climate during the heating season, moisture vapor inside a building is driven outward into exterior walls. When it reaches a surface that’s below the dew point, the vapor condenses into a liquid.” (source).
In this case that “surface” where moisture in the air condensates is that metal or fiberglass shell.
To try and work with this problem you need airtight insulation. This could be 2 part closed-cell polyurethane spray foam insulation. This offgasses too much for most people with chemical sensitivities. It also causes the challenges of exterior leaks going undetected. Arched Cabins has a nice design because there are no seams or permeations. The challenge here is when spray foam pulls away from the metal or fibreglass.
The second strategy is to use rigid foam insulation and make it airtight. This is also tricky. Foam can be taped or sealed with caulking or 1 part canned polyurethane spray foam, but it’s difficult to keep it airtight. And any gap of air behind the foam can have air with enough moisture to condensate in some climates.
Mold Preventative Design
- In heating climates, it’s easier to have a well-designed wall system that has the proper air barriers (likely no vapor barrier), and a rainscreen – in short, built like a regular house with all the complexities of the wall system but with great attention to design and execution of detail.
- A monolithic wall – I tend towards simple buildings that have fewer areas where mistakes can be made. Monolithic walls (a single wall, made of one solid material) is easier in this sense. Log cabins, solid concrete walls, and solid earthen walls are examples. This doesn’t mean they will work in any climate and are foolproof. You still need a building science expert (like an architect) to design the system as a whole and make sure that the wall type is properly designed and executed and well maintained.
Corinne Segura is a Building Biologist Practitioner with 8 years of experience helping others create healthy homes.
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