Building a Mould-Free Tiny House

Building a Mould-Free Tiny House 

This article will discuss preventing mould in tiny homes that are custom built. Usually on wheels, but much of this could apply to lane houses and other tiny homes not on wheels (though I don't discuss foundations here). This will apply to some prefab but not all types.

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

Water on ceiling due to improper vapour barrier
When I first set out to build my tiny house I was mostly concerned with choosing healthy materials that were 0-VOC. It was only after I took the house apart (almost completely) to fix the problems my builder made, that I realised the extent of knowledge needed to build a mould-free home. I thought you just leave the construction details up to the contractor, but my builder made almost every mistake in the book.

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

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

Here are a few different systems:
  • Passive house design - Passive house design is a very detailed system that uses a lot of calculations to manage the moisture in a scientific way. You can check out 475 to learn more about this. 
  • Breathing walls - Check out George Swanson who uses breathing walls and look up the science behind not using vapour barriers. 
  • Walls with vapour barriers - Learn the basics on vapour barriers and what smart vapour barrier are. 
  • Wood frame houses versus metal framed houses.
  • Building with SIPs.
Here are a few terms and ideas to learn about so you can follow along with your expert:
  • Flashing of windows and doors - the instructions on this are fairly simple and yet they are often not followed precisely (they need to be!) 
  • Taping housewrap - there is a controversy about whether to tape the horizontal seams
  • Rainscreens
  • Solar vapour drive 
  • Vapour barriers and condensation
  • Insulation types and their permeability 
  • Perm rating of a material/barrier
  • Air barriers versus vapour barriers
  • Ventilation - proper exhaust fans, ERVs, HRVs, and dehumidifiers
  • Exterior foam insulation method
  • Steel frames versus wood frames
  • Zip systems instead of housewrap
Do not attempt to become an expert on these topics from reading about them online. There is not enough information online to become an expert in these topics. You simply want to be informed so you can choose a good architect and understand the system they are designing for you. You may also need to learn enough to supervise the build.

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

Slats in my loft were a very good idea
  • Window and door flashing not done in a detailed way. Also beware of 0-VOC peel and stick window flashing which doesn’t fit most codes and is not recommend by the companies themselves for the rough openings. I have also seen windows flashed with housewrap tape and not proper peel and stick flashing.
  • Silicone and other caulks skipped where needed on the exterior due to chemical sensitivities.
  • Having air leaks into the wall cavity.
  • Housewrap not applied to spec -  including the overlap and how it is taped.
  • Roof not vented properly (there is some debate here between passive house design and most builders) or double vapour barrier issues in the roof.
  • Putting the vapour barrier on the wrong side.
  • Planning the house to be used with heating but not planning for AC.
  • Exhaust fans over the stove that don’t vent to the outside. Exhaust fans in the bathroom that could leak moist air into the ceiling. The fan I used is pictured (doesn't leak moist air).
Proper exhaust fan. Click pic for link.

  • Not having a professional plumber install your plumbing system. Or reusing old plumbing pieces that could fail on you. 
  • Pipes not designed and winterized for the climate causing them to freeze and burst. Not providing the cold and hot water a low point to drain outside. If the power goes out you will need to drain them. You may also want to drain them if you are away. 
  • Inventing a new wall system that is not normally used. Make sure you understand your wall system and which direction it dries to. Don’t skip on things like rainscreens (if that is the system you are using) just because it is a tiny house. 
  • Using wood that doesn't hold up well to humidity in the framing.
  • Putting your mattress directly on a solid surface with no ventilation under it (use slats or a box spring).
  • Using natural latex. See my warning here
  • Not using a properly sized drainage line on a heatpump. Know how to flush it out, this tends to get clogged with mould.

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    Mould Testing Overview - Pros and Cons of Different Methods

    First I want to talk about the most reliable test which is how you feel in the house compared to other places. Unfortunately this is not always as simple as it sounds to execute. There are different ways to undertake this experiment. The simplest way is to stay in your backyard in a tent or all metal trailer without bringing any possessions from the house. The most obvious complication here is that you will need to go inside to use the washroom unless you get a porta potty! You may also be so sensitive that the house has contaminated the air outside (I have experienced being outside of a house and being able to smell the mould).

    The next option would be to stay somewhere where other people recovering from mould illness (and MCS) have felt better. This could be a campground, KOA cabin, Airbnb or other rental. I have a lot more details on this in my post on the Locations Effect and Mould Sabbatical.

    Once you have gotten "clear" and done some recovering you might be wondering how do you test a house to find out if it's good? Some people can walk into a house and know if it's good for them. But even the most sensitive people usually need to request to spend 3 nights trialling the house. This is not always an option, but you should ask. Usually people sleep better in a house that is mould free, but me and other CIRS patients have found that there is some mould that puts you into a zombie sleep where you sleep more (and then get sicker). So even a three-night test can be tricky.

    It is also good to verify the house is safe with mould testing. The most common test for CIRS (mould patients) is the ERMI. It is highly recommended by Shoemaker certified doctors as the test to use. The range of the ERMI scores goes from minus 10 to positive 20. You need a score or 2 or lower to be treated and recover from mould illness according to Dr. Shoemaker.

    Other types of mould tests can also be useful. A tape lift will get you definitive results on visible mould. I look at the options below. This is a very simple overview just to give you the general idea of what is out there in a way that is not overwhelming - you may want to look more into each of these different methods. Please note that my sources were biased towards mould advocates Lisa Petrison from Paradigm Change, Greg Muske from Biotoxin Journey, Dr. Shoemaker and Cheryl Ciecko, an architect who specialises in mould. I have attempted to cross-check their information. However, going with information from the companies that do house inspections can be biased and contradictory. (All sources at end of post, which you can read for more detail).



    - Doesn’t work well in brand new houses.

    - You need dust that has settled for a while (wait 4-6 weeks to re-test an area).

    - Having very little dust or a high amount of dust can skew results.

    - Having a high amount of outside dirt inside can skew results. Having high or low outdoor spores counts can skew results.

    - May not be an even distribution of spores throughout the house if mould is only coming from one place and the house is large.

    - It is known to miss major mould problems when people are very sick in their house. Similarly, after a remediation, a CIRS patient can still be sick from the mycotoxins left behind despite a low score.


    -"Only the ERMI and HERTSMI have been associated with sequential activation of innate immune responses, not air testing.” Dr. Shoemaker. Meaning it is the only test that he found that is consistently in line with lab results for CIRS, despite its drawbacks.

    - Vacuum method can pick of heavy spores like Stachy and the Swifer method can also be used to pick up places with accumulated dust that has been there for 4 months. John Banta always tries to use the vacuum method over swipe method.

    - It's pretty affordable at $300. You do it yourself. The lab recommended is Mycometrics.


    -Similar to ERMI but tests for a handful of moulds most commonly associated with water damaged buildings. It is cheaper than ERMI. I would go for the full ERMI and you can still calculate your HERTSMI value from that. Shoemaker certified doctors will consider your HERTSMI score as well as ERMI score.

    Tape Lifts


    - You need to have visible mould.

    - It assists you with what type of mould it is and not how widespread the problem is.


    - Tells you what kind of mould you have when you have a visible sample.

    - Allows you to know if this is a toxic mould.

    - You can do it yourself.

    - It's the cheaper way to test for visible mould.

    I used this DIY Tape Lift to test a few areas in a house I go into often. The results came back showing me what type of mould it was. It confirmed that the mould was one that is toxic that comes from water damage. Though you need to get a decent amount of mould on the tape otherwise your results will just show scattered pieces.

    Spore Traps (Air Test)


    - Needs to be taken near the source, so you have to know where the source is.

    - Shoemaker says: "The industry standard of sampling the air for spores is not an acceptable substitute for many reasons. One of the main limitations is that over 99% of the particles that carry the inflammagens from water damaged buildings are smaller than 3 microns. Spore traps can only detect particles that are larger than 3 microns and therefore, miss over 99% of the inflammagens.”

    - Spore traps identify round, intact spores. So they will not catch evidence of past problem that have left mycotoxins.

    - Can miss/underreport certain heavy species like stachy.

    - Expensive.


    - The test is more standardised than tape lifts, swabs, cultures, and mould-dogs, they claim.

    - It is the most widely used mould test.

    - You can compare inside and outside air.



    - Hard to know where to place the dish to get capture the mould if you don’t know where the mould is coming from.

    - Doesn’t get you an accurate relative reading since some mould is harder to catch and some proliferate faster in the dish than others.

    - Stachy is a slow grower compared to other moulds in the dish.


    - Can be used in multiple places to compare and for general observation.

    - Can give you more details on the exact type of mould than other tests.

    - Inexpensive.

    - John Banta does a culture of the dust used for ERMI to compare and get more details

    Here is one you can do yourself.

    Mould Dogs


    - Can only detect a handful of moulds.

    - Hard to know if they are well trained, look for good references of the company.

    - They can’t tell you if it’s high amount of mould or a trace from after a remediation.

    - The dog can only sniff in areas where they can reach.


    - They are good at finding the source if it is within their reach.

    - The dog can smell both live and dead mould.

    - You can pinpoint the area where you need to do further testing.

    VOC testing


    - There is controversy around the accuracy of this testing.

    - Not widely used.


    - Test the levels of mycotoxins and other VOCs in the air.

    Here is a company that does this kind of testing that is recommended. It goes to an AIHA accredited lab.

    Public postings by Cheryl Ciecko (Architect)
    John Banta interview
    Dr Shoemaker Q&A

    Converting a Cargo Van - Chemical & Mould-Free Camper Construction

    This post will cover converting a cargo van into a camper. I will focus only on a few key areas. The key factor here is insulating in a way that will not go mouldy - as metal walls are the trickiest thing to insulate because of the condensation factor. I will also look at MCS safe materials for the interior, and a few appliances that are recommended by others. Building a camper that will be both mould-free and chemical-free is tricky!

    Keep in mind a cargo van can be anything from a metal box with a bed to a fully decked out camper with a stove, fridge, sink, heater, AC, and even a full bathroom. 

    This will also be a review of the technical aspects of Camp Like a Girl and The Vanual

    Insulating a Cargo Van 

    The most important aspect of creating a mould-free camper is the insulation. Here is the key point: no water vapour can enter the wall cavity. With exterior metal walls, as soon as you are heating the van to the point where the exterior wall will be dewpoint, you have a serious risk of condensation and mould in the walls. So again, to keep it simple, no water can enter the walls if you plan to heat your camper when it's cold. 

    Rigid Foam

    The Vanual
    In Camp Like a Girl, Sara uses some XPS and some EPS insulation. XPS is a vapour barrier (meaning no water can pass through 1.5 inches), and EPS is not. So using XPS foam is one option to insulate your van.  XPS or polyiso with foil backing are usually tolerable for most people with MCS. Johns Manville Polyiso is the only foam without flame retardants. 

    However, just the foam on its own will not be airtight. You can used canned spray foam to fill in the gaps if that is tolerable for you. It is not chemical-free but I have found it odourless once dry. Handi-Foam is the safest one, as it is GreenGuard Gold certified.

    If you are putting the plastic covers back on the walls like Camp Like a Girl, I would silicone/caulk around those to make it airtight. The most tolerable caulking is Eco-bond.

    Robert Lawson, another van owner, is trying this strategy to fill in all the gaps: he says: "I have 1-inch polyiso foam on the walls and ceilings. I plan to put Reflectix between the foam sheathing and the steel body so there will not be an air space where condensation could form. I will put another layer of Reflectix on top of the sheathing as well in order to cover all the irregularly shaped frame members."

    Camp Like a Girl also uses insulation in the bed platform to keep the bed warm. Here I would definitely go for insulation that doesn't have flame retardants instead of XPS. If you are putting your bed on something solid in a camper I would cover the bed in a plastic waterproof cover otherwise it's a mould risk. 

    Spray Foam

    Spray Foam is going to be your safest bet for preventing mould, as the foam will get into every crevice and form an airtight layer that will prevent all moisture from getting into the walls.

    The best spray foams are Heatlock Soy line at Demilic (GreenGuard Gold certified) and Icynene Proseal (GreenGuard Gold certified) (closed cell). Both are polyurethane foams, from reputable companies that are usually easy to source. It must be closed cell, which is a vapour barrier. I recommend these to healthy people who are set on spray foam. I don't usually recommend them to people with MCS because I have heard bad stories (and there are better options for most homes). However, I have an extremely sensitive client who can tolerate Demilic. In theory, they do not offgas, but if not done perfectly they do, and that is a huge risk.

    It is worth considering in a van, especially if you are mould sensitive but not chemically sensitive. You can also then try and put a vapour barrier over this or use metal walls to prevent the possible offgassing from the spray foam from entering your space. 

    Walls and Ceiling

    Metal is your safest bet unless you are putting the plastic covers back on. This all depends on what kind of van it is, as they are all different. But if you can use metal walls, that is your safest bet. For an extra layer of protection, caulk around the seams to prevent moisture from going in the walls. If you are not using spray foam or canned foam then this caulking sealant around the walls is crucial.

    Sara used PVC ceiling tiles which are toxic, but real tin ceiling tiles could be used as a non-toxic alternative which add a fun look to your camper. 

    While The Vanual looks very pretty with its wooden ceiling, but I would avoid plywood as walls, ceiling or subflooring. There are just too many points where the wood hits the metal. If you are intent on getting this look, you would have to have lots of insulation at all the metal ribs to make sure dewpoint would never be hit. If that is possible, then you could use formaldehyde-free plywood with strips of wood over it to get the look in The Vanual. 

    Marmoleum floors

    I wouldn't feel comfortable using wood to raise the floor joists as the wood right against the metal could be a recipe for condensation and mould. Riged foam may be your best bet for floors to solve the thermal bridging there. Or else spray foam between the joists and then use metal flooring.

    Different flooring materials could be considered - metal, which could be painted with different designs for a pretty effect, or covered with rugs, or Marmoleum (if you can tolerate the smell of natural linseed oil). You could also cover it with EVA mats. You could use wood if you are sure you have enough insulation underneath to prevent condensation from forming under the wood (and the wood can withstand high humidity). MgO board could be used as subflooring here if you are using Marmoleum or wood. The MgO will crack though.

    Interior Structures: Bed, Cabinets

    The Vanual
    Sara and the Vanual used plywood for their bed bases which if softwood plywood needs some time to offgas formaldehyde and also doesn't let the mattress breath. Mattresses are very susceptible to becoming damp in campers. It would be best if the bed base was made of planks that allowed some airflow. The bed should be flipped and checked often for dampness, especially if you cook or shower inside. Even better, in such a humid environment cover the mattress with a waterproof protector before installing it in the camper. This one is highly tolerable.

    For cabinets, if you do use hardwood plywood, go for a formaldehyde-free plywood like Purebond or use solid wood.


    You need fans that move air out - one above the shower if you have one, and one in the general space. My CampLite had two fans and we still have problems just with cooking humidity making the mattress wet. The standard camper fans are Fan-tastic.


    The Vanual has some cool tips for solar power, wiring and appliances. If you want to go off-grid you will need solar and you will need to tolerate a fuel stove. The Vanual and other van owners speak highly of Goal Zero solar systems because of how easy it is to install. See comments in this post on others who do not like it.

    The other option is to wire the van to plug into a campground plug (or modify to plug into a house), this would allow you to cook on an electric hotplate and would allow an electric heater. Using an electric blanket or pad is  a good heating option to save energy.

    For off the grid heaters I would go with the rooftop propane heater/AC combo that many trailers have. Though extreme mould avoiders have said these can get mouldy.

    I would not use the stand alone propane heaters that go inside as they will not be safe for those with MCS.

    For cooking, if you are off the grid you will need to burn some fuel to cook. Cooking outdoors is safer. Alcohol burning stoves are safer than propane. Though this won't be tolerable for many.

    For a fridge I would go with a 3-way fridge that can run on propane solar or AC electricity. Unlike in most trailers propane is stored inside so this could become a problem. The Vanual recommends running this fridge on solar or the car battery.

    An Overview of the Process

    I like this YouTube video because it gives a good overview of the whole process and how complex it is. With a few tweaks this van could also be very suitable for a chemical or mould sensitive person.

    If the insulation is sealed up perfectly by the Reflectix and tape, than no vapour will pass through. If you have a high enough R-value to keep the wood walls from getting condensation then this could work. (You would still want to use a wood that holds up well to high moisture areas).

    A few materials need to be tweaked: use solid wood - no laminate or plywood, natural bedding and cushions, slats under the bed for airflow (which I think he did), gas stove may or may not be tolerable, a better extraction fan, and I would look for an alternative to that vehicle carpet.

    Here is an example of one custom made for MCS, you would want to see how the construction was done.


    An All Metal Tiny Home

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

    Here are the specs:

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

    The trailer is a custom welded steel channel beam trailer.

    There are options for the paint used on the trailer.

    The frame all ready to go! Photo: Tiny Green Cabins
    Steel Underbelly 2 x 4, 16 gauge joists.
    The cold-formed steel joists are bolted to the trailer frame.

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

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

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

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

    For the bathroom there are different options - yu can have RV hook-ups or a composting toilet andgrey water system. (Nature's Head is the best composting toilet. Others like Sunmar have major issues.)

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

    Fabral smooth painted steel to wrap the exterior walls, and Fabral “w” metal roofing for the roof. Metal at walls is riveted and steel roof and trims screwed. Fabral should be tested first to make sure the paint finish is tolerable. Other metal finishes are available with different brands.
    Ceiling is corrugated steel.
    Interior walls are Fabral steel attached with screws. Interior comes in different colours, or can be painted later with metal primer and paint. Caulking is used to prevent water vapour from entering wall cavity.
    Metal flooring is 2 layers of 18 gauge steel layered. Foam is used as a thermal break and insulation.
      Doors are metal and glass.

      Insulation options are XPS foam or Johns Manville foil-backed polyiso (the late is the only foam without flame retardants). Foam is being used as exterior sheathing/thermal break as well. Other materials could be considered for insulation but riged foam was our top pick here. Tyvek tape is used to seal the sheathing if tolerated. I would also caulk the insulation or walls on the inside side for an extra barrier to water vapour entering the walls.

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

      For a hot water heater we are using propane on demand. This is the best way to go for water to keep the house to 50 amps or less.
      Exhaust fans are very important in an all metal house to keep the humidity as low as possible. In the bathroom it should be exterior mounted as to not leak moist air into the ceiling. An ERV could be a good option if you have a composting toilet (this depends on your climate as well). In the kitchen the exhaust fan needs to vent to the outside. A dehumidifier may also be needed if condensation forms on the walls or the mattress becomes damp.

      For appliances, a propane fridge should be considered to reduce electricity needs (2-way or 3-way refrigerators can be good depending on your needs and if you are incorporating solar). An apartment sized stove can be used or else a small convection oven with a cooktop. If you can tolerate propane or alcohol stoves those can be considered for an off the grid house.

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

      I can help you work with your builder to come up with a customised list of materials that will work for you and your tiny house. Please see my consulting page for more details and contact info. Tiny Green Cabins specialise in building for people with sensitivities. Thanks to Luke Skaff for help on the technical aspects. Always consult with an architect or engineer on moisture management in your building envelope.

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      What Green Certifications Mean for Those With MCS

      Here are some of the most common certifications for VOC levels and what they mean for the chemically sensitive.

      Green Label Plus - Certifies "very low" emissions on carpets. They test for 35 compounds listed under California Department of Public Health’s Section 1350. Each product category also includes additional compounds for certification, six for carpet, two for carpet pad, and seven for adhesive. They meet or exceed California’s indoor quality standards for low-emitting products used in commercial settings such as schools and office buildings. Here is the list of their levels of VOCs. I would find these levels to be too high for people with chemical sensitivities.

      Green Seal - Follows CARB levels of VOCs (more on CARB below). For example, on paint, this is between 100-300 g/l depending on the type of paint. This is not a low enough level for people with chemical sensitivities.

      GreenGuard - GreenGuard has two levels of certification, GreenGuard - 500 μg/m3 total VOCs, and GreenGuard Gold - total VOCs 220 μg/m3. (GreenGuard Children and Schools which also measured for phthalates no longer exists). For reference, the average house has a total VOC level of about 200 μg/m3 and the outdoor rate is about 1/10th of that. GreenGuard levels claim to keep VOCs below limits that would adversely affect health. However for extremely sensitive people the level in an average house is unacceptable, so GreenGuard Gold level may not be tolerable. I recommend GreenGuard Gold for people who are healthy but I would always aim for outdoor levels of VOCs for those who are ill. Because it states that the levels are below the given threshold, you don’t know if the product is 220 or 0 μg/m3. You still have to contact the companies to find out what the VOC level is. Note: GreenGuard measures the emissions and not the content in the material so these numbers cannot be converted to g/l.

      OSHA Guidelines - CA OSHA has the strictest government guidelines for VOCs in buildings. Here are their limits on VOCs. While CARB and OSHA are definitely steps in the right direction, they promote levels of VOCs that will not cause adverse effects in healthy people. These levels will not be acceptable for the extremely sensitive.

      CARB - Establishes a maximum VOC-content for consumer products sold in California. These are not necessarily low VOC. For example, low-VOC paint means less than 50g/l, while CARB levels for paint are 100-300 g/l. (Note: zero-VOC means less than 5g/l)

      Certi-Pur - Certifies polyurethane foam. All polyurethane foam can basically meet this level of 0.5 ppm (or 500 μg/m3 total VOCs).  A level that is too high for most sensitive people. They would not give out info on how long it takes to completely offgas. While this certification provides a maximum level of VOCs, some polyurethanes can be as low as 72 μg/m3 which would be an acceptable level for many people. It also certifies that they are made without PBDE flame retardants (although they almost always do contain other flame retardants). They say the are made without formaldehyde but the limit for formaldehyde in the foam is actually 100 μg/m3 (compared to the GreenGaurd Gold limit of 9 μg/m3). They say made without prohibited phthalates (not free of all phthalates).

      What Should the Chemically Sensitive Look For

      I always choose zero-VOC materials when available. You can find zero-VOC options for wallboards, insulation, siding, sheathing, flooring, paints, sealers, caulking, grout, thin set, tiles, beds, furniture, flashing, windows, roofing, and underlayments.

      Also, look for products without flame retardants, biocides, phthalates, and lead. (These are not listed as VOCs).

      There are very few areas in which we have to use VOCs such as pipes, some glues, wiring, and appliances. Flame retardants cannot be avoided in appliances and electronics.

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      Now Certified as a Building Biologist!

      Hi everyone,

      I am now certified as a Building Biologist with the International Institute for Building-Biology and Ecology. The Institute's mission is "to help create healthy homes, schools, and workplaces, free of toxins in the indoor air and tap water, and electromagnetic pollutants."

      This certification has helped me deepen my knowledge of how we can create homes that will aid in improving the health of their occupants.

      I am available for consultations by phone and email and can assist you with the following areas:
      • Choosing zero-VOC materials for a new build or renovation
      • Selecting non-toxic materials best suited to a tiny house
      • Discussing common trouble areas and mistakes made in the build of tiny homes
      • Sourcing special order zero-VOC materials 
      • Remediating a home that is toxic or scented
      • For those wishing to go GreenGuard Gold, selecting conventionally priced materials that are very low in emissions
      • Working with you and your builder by providing ongoing materials selection and sourcing support throughout your build
      • Tips for building a mould-free home
      • Experience with which materials tend to work best for the most sensitive individuals
      • Selecting non-toxic furniture, decor, bedding and other household items for your home
      • Research into the toxicity profile of specific items or materials you are interested in using
      • Choosing the best water filter for your home
      • Buying, customizing or building a less-toxic trailer, camper or RV 
      You can also opt for a team approach with a Building Biologist and Engineer to help select the best non-toxic materials that fit the technical needs of your build.

      The rate for consultations is $50 per hour. Feel free to email me at corinnesegura[at]

      Zero-VOC Sheathing & Subfloor

      Here is an overview of low-VOC and zero-VOC sheathing and subflooring options.

      Structural Plywood

      Structural plywood (Softwood Plywood - SWPW) can be used for exterior sheathing, roof decking and subfloors. It is made with phenol-formaldehyde glue (PF) in the US and Canada.

      The Rate of Formaldehyde Offgassing in PF Plywood

      "Formaldehyde levels in this test chamber were well below 0.1 parts per million (ppm) in air from all tests of fresh panels, and emissions rapidly approached zero as the panels aged. In fact, the levels were so low and so close to the "background" levels in the test chamber that is was not possible to measure them accurately." Source APA

      The rate in outdoor air is about 0.0002 - 0.006 parts per million (ppm) in rural and suburban outdoor air. Source

      While 0.1 ppm is high for someone sensitive, the fact that the panels rapidly offgass should make them tolerable for someone with MCS. I would suggest testing plywood that is a few months old.

      A Note on Purebond Formaldehyde-Free Plywood

      Purebond plywood is not rated structurally or moisture-wise for sheathing, subfloor or decking. I have spoken to the company and they don't recommend it used for this purpose though I do see people building with this product. I am not sure the consequences of building your subfloor or decking with a non-structural plywood.

      Non-Wood Options:

      Exterior Sheathing

      A non-wood option is Georgia-Pacific DensGlass, which is around 3 times the cost of OSB. It is very low VOC; they are going for GreenGuard certification. It is also a lot more mould resistant than OSB or plywood. Make sure with all materials it fits the codes where you live (in terms of high winds and earthquakes). Make sure it is also compatible with your exterior finish.

      MgO board is now starting to be used as exterior sheathing. Another zero-VOC option. It is heavy, structural and more expensive than plywood.

      Rigid foam can also be used as exterior sheathing without any ply or OSB. The rate of XPS offgassing is very low, but it does contain a flame retardant. The other option is Polyiso. The Johns Manville brand does not contain a flame retardant. Here is some info on how to brace when using rigid foam as sheathing. This is not structural and should be checked against local codes.

      Another structural option is Rewall which is made of recycled beverage cartons and cups shredded and compressed. It claims zero-VOCs. It is paper-faced.


      It is possible to use structural cementitious sheeting board (MgO) as a zero-VOC option however when I did this in my tiny house I needed additional framing support underneath. It worked out well for me. Here is an example of the support you need underneath. This is probably only suitable in a tiny house.

      For those who can't tolerate wood it is possible to pour a concrete upper floor.

      Roof Sheathing (Decking)

      Purlins or skip sheathing can be used as an alternate form of roofing which eliminates the need for solid sheathing. This will only work with certain roof types (metal vented attic, in some cases cedar).

      Pre-Plywood Options

      In the days before plywood, solid wood was usually used:

      For exterior sheathing, 1-by lumber laid diagonally was used. This is not an airtight option so humidity and energy issues should be considered. Make sure to use housewrap. Consider double sided housewrap tape so that you get more of an air barrier.

      For subfloors, 1-by subfloor were laid diagonally to the floor joints. The subfloor could be planks or tongue and groove. Here is a little more info and a pic of planks. This is a zero-VOC option but it will cost you quite a bit more. If you use this method make sure you use a subfloor adhesive otherwise you will have a very creaky floor. Liquid Nails is the lowest VOC option I have seen at less than 20g/l, but I find Almighty Adhesive to be more tolerable.

      For decking, 1x decking butted up to each other can be used. This is how roofs were built before plywood or OSB. This will allow for many types of roofing types over it.

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