This post is an overview of low and zero-VOC sheathing, decking, and subfloor options
This post contains affiliate links to relevant products that I use and recommend. Upon purchase, I earn a small commission at no extra cost to you.
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 the 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 it was not possible to measure them accurately.” APA Source
While 0.1 ppm is potentially high for someone sensitive, the fact that the panels rapidly off-gas makes them a safe option for most people with chemical sensitivities.
If you are building new, I would suggest testing plywood that is a few months old before ruling it out.
For a detailed review of the glues and chemicals that off-gas from plywood and OSB sheathing see the post on formaldehyde and pressed wood products.
A Note on Purebond Formaldehyde-Free Plywood
Purebond plywood is not rated as a structural plywood for sheathing, subfloor, or decking.
It also doesn’t handle moisture as well as typical plywood.
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.
Please don’t do this!
Purebond is made with “soy-based glue” which can be quite tolerable for the chemically sensitive.
Plyboo is a bamboo-based plywood made from soy glue as well, and is also not structural.
Exterior Sheathing Options
The three main types of sheathing are: plywood, OSB, and Huber’s OSB.
If you use something else, the first thing you need to do is check with your building codes and also consult with an architect to make sure you have the structural support needed.
Plywood is the best option for most sensitive folks.
OSB take longer to off-gas in my experience (and most chemically sensitive folks’ experience).
I talk about Zip Sheathing and Zip-R in the book and course.
There are other options apart from plywood and OSB for wall sheathing.
They are usually more expensive, some are unadvisable, and not all meet codes.
These unusual options are outlined in the book and course.
Subflooring
Sub-flooring is usually plywood, OSB, or AdvanTech (which is a form of OSB).
You can also use solid wood.
Alternatives and subfloor glues are mentioned in the book and course.
Roof Sheathing (Decking)
Plywood, OSB, and Huber products are also the most common roof decking.
In some cases/some designs, you can build without any sheet decking.
You also need to consider the adhesives that are required with certain types or brands. I mention that in the book and course.
Corinne Segura is an InterNACHI-certified Healthy Homes Inspector with certifications in Building Biology, Healthier Materials and Sustainable Buildings, and more. She has 10 years of experience helping others create healthy homes. You can book a consult here.
A Jones
I’m in a house built in 1950-1966. There is no flooring down in the upstairs largest bedroom. If took a while for the smoke smell to go completely from the previous tenant. A year Infact. I’m definitely chemically sensitive. The subfloor smell is so strong that I can’t bear to be in there. It’s a housing association property (I’m in the UK) and I’ve requested they visit to see if anything can be done. I had a handyman mentioned was “glue”. I’ve sprinkled bicarbonate of soda a few times but this only makes the smell milder. As soon as I hoover it, it returns. The house was built in between 1950-1966. The subfloor will be this age. Do you have any recommendations please? The housing association repair men won’t be experts. I think they’ll be unlikely to offer a proper solution.
Corinne Segura, Building Biologist
I have an article on removing smoke smell
Simone Mellor
I am insulating and putting drywall up in my ADU garage conversion. The existing exterior walls are just the t1-11 siding and framing- no sheathing. My contractor recommended we use Pro Clima Aerosana Visconn to paint the insides of the siding and framework. Do you know much about this product and its offgasing?
-Simone
smellor23@gmail.com
Corinne Segura
I don’t know anything about it but they may not list VOCs if it’s meant for the exterior. I would consult with Cheryl Ciecko on if this is a good idea as this is not a proper wall like in a house.
Simone
Thank you Corinne. I will reach out to her.
Joan
Corinne,
We are putting a new white oak floor in an apartment that had been owned by a smoker. I have MCS. The contractor went ahead and put in an Avantech subfloor without my knowledge. Will we need to pull it up and use a plywood subfloor or is it possible to off-gas the Avantech? Help.
Corinne
That depends on how sensitive you are. You have to go by your own reactions.
Joan
Thank you for your reply. It will be costly to pull up the Advantech subfloor and put in a new plywood subfloor. You had written elsewhere that it takes four months for Advantech to off-gas. Does it off-gas in that same amount of time once the floor boards are on top? After the four months with the floor boards on top, should it be okay? One option is for me to stay in my current apartment and move in after four months. In your reply to Kathleen in 2020 you had said that some people might find Advantech and plywood to be similar. I am not sure what to do. Thank you for your help.
Corinne
4 months is how long it took at my level of sensitivity which has been a useful gauge in the past for probably 90% of sensitive people. depending on what underlayment and flooring you put on top and what’s below it it will restrict offgassing to some degree and slow it down.
Dorothy M
Hi. I’m about to spend a boat load of money on having my house’s old stucco removed and the fiberboard (from the early 1980’s (possibly Celetex) removed. Then the building re-sheathed and re-stuccoed. The contractor wants to use OSB followed a waterproof membrane followed by a thin insulation board followed by lathe and then the cement stucco brown coat then color coat. I’m wondering: would Barricade Thermal Brace be more energy efficient and less toxic than either OSB or Plywood?
Corinne
I would not use a fiberboard sheathing
Brooke
Hi there!
You mention the Zip R sheathing system. Is this system typically tolerated by those with MCS? I see that it has foam, so I’m very curious. I know you do not like 2 part spray foam, so is the Zip system foam completely different and does it not off gas? I have MCS and considering the Zip R system with mineral wool insulation. Would the foam on the Zip R system be considered the vapor barrier?
Thanks so much! LOVE your site!
Corinne
the OSB part would not be tolerated by those with severe MCS, the foam does not really have any offgassing other than when you cut into it and a little is released from the closed cells.
Brooke
Thank you!
Does OSB take a long time to off-gass?
Would the foam on the Zip R system act as the vapor barrier if one were to use Rockwool, Havelock, or fiberglass batting?
Corinne
OSB does take some time to offgas. The polyiso is not technically a vapour barrie but it’s of such low permeance that it’s treated like one. You can make your dew point calculations as if it were.
Brooke
Thank you Corinne! I appreciate your advice and blog!!!
Paul
I’ve decided to use exterior grade plywood (CDX Exposure 1) as underlayment for wood flooring, Can you recommend a safe subfloor adhesive?
Corinne
In the adhesive post. AFM usually the way to go.
Jen
If exterior grade plywood (CDX Exposure 1) is used for underlayment for wood flooring, is it necessary to air it out onsite? If so, for how long? Should it be sealed with an acceptable vapor-barrier sealant or that unnecessary?
Do you recommend avoiding Advantech subflooring due to the adhesives?
Thanks for all of the information you provide!
Corinne
Whether you need to air it or seal it or not depends on your sensitivities. I wouldn’t do either, personally. Avantech has more offgassing even without the polyurethane sealants needed. So if you are at the level of considering sealing plywood that would be way worse.
Jenna
I made the mistake of painting my subfloor to get rid of pet odors before laying new carpet a couple years ago. Now I’ve developed tinnitus and I think it’s from the paint off-gassing through the carpet (carpet was tacked down, not glued). For peace of mind I want to just get rid of the paint. Do I need to completely replace the subfloor, or would a layer of visqueen prevent the chemicals from getting into the air?
Corinne
I doubt that paint is offgassing after 2 years but it is possible. I would use sealants if that this the problem. Check out the posts on sealing in offgassing.
Dean
I want to apply a water proof sealer to the Weyerhauser 3/4 inch edge-gold subfloor to repel water between the beginning of September and mid October to guard against the elements (rain) in case we get a early rain storm this fall. The house I’m building won’t have a roof and be dried-in until late October. Is there any low VOC sealer that you could recommend that I could apply by either brush or sprayer?
Daniel Parnell McCarter
When installing a plywood subfloor over a concrete slab, are adhesives or glues needed or used typically?
Also, do you think it would be worth painting the plywood subfloor with a non-toxic sealer (like from https://www.afmsafecoat.com/) to seal in the low amount of formaldehyde that is in the plywood?
Thanks!
David Duke
If I used Dennyfoil behind my drywall would that prevent the exterior plywood from off gassing into my home?
Corinne
Plywood offgasses quite quickly on its own. The danger of an interior vapour barrier like denny foil is condensation and mold in most conditions where AC is used.
David Duke
Thank you!
Kathleen Beine
You state that PF plywood subflooring is preferred over Advantech, but you don’t say why. Both products use phenol formaldehyde resins, and the amount of resin in each product is similar. Therefore, formaldehyde emissions from cured PF plywood and from Advantech should be similarly low. Both products, and other similar products, are considered by US Dept of Housing & Urban Development to be insignificant. Because their emissions are so low, these products are exempt from California Air Resources Board regulation. So, why do you prefer PF plywood over Adventech for those who are chemically sensitive?
Corinne
Advantech has PF and MDI glues. There is more glue the more the engineered product is made of smaller pieces. Advantech is more impregnated with resin which makes it more durable than regular OSB. Usually sensitive folks prefer plywood but you may find the two products similar or you may have a preference for one or the other. CARB focuses on interior wood products only not structural.
Unknown
I do not see any links?
misha
We used it as flooring on the 2nd floor of the house we're building. Also going to use as inside walling and outdoor decking with tiles over the top. We used Modakboard MgO board from Australia. Great company! Sent samples wrapped in foil for me and everything.
CriegerGoodwin
What about MgO Board? George Swanson, builder from Austin, TX, uses MgO for exterior applications as well as interior. I think he also uses it for roof sheathing… Thoughts?