Updated in Spring 2020
Simple, Small Modular and Custom Homes for those Sensitive to Mold and Chemicals
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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 built any size.
Their predesigned wing is called Unity Homes. Their smallest house “Nano” (pictured) is 477 sq ft. Nano Shell packages start at $65,000, and for a complete house it would be roughly $150,000.
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 buils and indoor factory conditions.
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
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. 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 preventing possible condensation without the air pockets of the wood wall.
That is how I would detail it for mold prevention. This would make it quite pricey.
$35,000 BASE PRICE (CAD) for the 93 sq ft little module.
3. Metal Yurts
The metal yurt from Clean Air Yurts is 18 ft in diameter. The shell is made of galvanized steel coated in zinc. The door is metal as well.
You would need to build a foundation and choose materials for the exterior and interior, provide insulation and wiring and plumbing (if desired).
Though you could just leave it as a steel structure. The yurt can be assembled in one day and can be taken down and moved if needed.
Metal walls are very difficult to insulate in cold climates. In a cold climate you would need a perfect air tight insulation. See the section at the end about exterior vapour barriers in cold climates. Metal houses can work well in places where you don’t need insulation.
In some very dry climates, you can get away with loosely fit foam insulation but you would want to be able to check on that and make sure there is no condensation behind it.
The cost of the metal yurt is 10K
Grain Bin Home – Another Yurt Like Option
These Grain Bin Homes are also 18 ft in diameter and made of galvanized steel. There is room for a loft and it has louvers that can collect rainwater if desired. Other options include solar panels.
It does not come with options for interior/exterior or foundation, so those would be up to you.
The homes are around 10K but there is a big discount for non-profits who are purchasing them.
Same as above section regarding metal walls – tricky to insulate in heating climates.
4. 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 are $450 and that includes a 3-hour consultation. The metal parts are $2000-2500 and the wood would come to around 5-10k, not including materials for wiring and plumbing.
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.
5. Arched Cabins
The basic kit for Arched Cabins includes kits include 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 vapour barrier and the best bet for insulating metal walls in heating climates.
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.
6. 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).
The domes start at $7,500 for the 14′ model in 2017.
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.
A similar dome, the Intergalactic, is also fiberglass, and the insulation is integrated.
7. 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.
8. 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. A similar company, AluHause is American, with a show house in Palm Desert.
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.
Just like when looking at larger prefabs you have to go through the reconnaissance process outlined here.
The Coodo is 61K British Pounds for the base model.
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.
9. Simple Wooden Cabins
Solid wood very basic wood cabin
Leisure Cabins bare bone wooden cabins are made of solid wood. I see some OSB in the subfloor but that could be avoided. Opt for solid wood for the roofing as well.
There is no insulation so they would be difficult to live in in extreme temperatures.
It does not include roofing shingles and roof prepping, stains, railing, foundation and deck or windows. You do your own wiring, plumbing, and systems as well.
This version is a thin wood wall, not very warm. And when you start to insulate something like this you start to get into a complicated design.
In that case I would prefer to go back to a prefab like the Unity Homes on this list which already has a well thought out wall system, or even design a house from scratch.
Trying to make one of these kits work with insulation is working backward from a plan that won’t likely come together in a mold preventative way in climates where heating is used.
It is $6500 CAD for a 14 x 14 foot cabin. They are produced in Canada.
Amish Built Wood House
From Backyard Buildings in Maine, these tiny houses are a good deal. They are custom built. This one pictured is from a member of the EI groups on Facebook and I have her permission to post about it.
The house is made of local wood, non-fiberglass insulation, low VOC adhesives, a woodstove (but you could use electric heat), wired for on-grid (but can do off-grid as well), cedar siding, metal roof, and plumbing.
This does become a complicated system to design when you add insulation.
When I tried to work with this company, it was difficult to communicate with the builders (because of lack of technology/being Amish). They were mixing some traditional building with some more modern techniques like adding exterior foam insulation and I didn’t think it was mold-safe or detailed right.
They can be moved though they are not on wheels. This one is 400 sq ft and was only 14K. I would only get a shell if buying something like this so that you can detail it yourself.
When buying a shell you also want to make sure it has a rainscreen if you are going to insulate it, otherwise you won’t be able to build that out properly.
A Traditional Log Cabin
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
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.
10. A Metal SIPS House
The Nomad Micro is a metal SIPs house. It can be built out to be very non-toxic.
They are 28K CAD for the 10×10. You need to add: shipping (From Vancouver BC), platform or slab, installation, wiring, heat, plumbing, hot water heater.
There is an option to complete the inside with non-toxic materials. My most sensitive friend tested the SIPs and thought they were good.
Nomad has stopped production of the 10 x 10 and only produces the 13 x 13 now. They have also changed the basic design of the units since I first posted this.
I do see wood mixed in with this metal structure which I would remove in the design.
But the basic design is metal framing with metal SIPs, and I still think this is a good idea.
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, but I have not been able to have a full review done by an architect. In theory a metal SIPS house could work really well for mold and chemical sensitivities.
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 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.
The houses are 15K and 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 that 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 rood, 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 vapour 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.
Humidity Control is Required
Climates that are hot and humid should use AC or a dehumidifier in any concrete building. AC acts as dehumidification.
It can take 2 years for concrete to fully dry and in humid countries that don’t use AC, concrete goes musty fast.
Many people might not notice this low level of mold but I can smell it and mold sensitive people do often react.
I’ve stayed in many simple concrete builds in the tropics.
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.
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 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 as maintained.
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Corinne Segura is a Building Biologist with 6 years of experience helping others create healthy homes.
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