This post is an overview of low and zero-VOC sheathing, decking and subfloor options
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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 is was not possible to measure them accurately.” APA Source
While 0.1 ppm is high for someone sensitive, the fact that the panels rapidly offgas make them a safe option for most people with chemical sensitivities.
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 offgas 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 likely means polyurethane. I do not prefer this over regular plywood.
Plyboo is a bamboo-based plywood made from soy glue as well and is also not structural.
Exterior Sheathing Options
There are other options than plywood and OSB for sheathing. 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.
It’s highly unusual to use anything other than plywood or OSB. Solid wood can be used but it’s very pricey and not done often. Non-wood options are far riskier.
One non-wood option is Georgia-Pacific DensGlass gypson, which is around 3 times the cost of OSB. It is very low VOC.
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 sometimes used as exterior sheathing. Another zero-VOC option. It is heavy, structural and more expensive than plywood.
It is not often recommended by building science experts, proceed with caution regarding the fact that this is prone to cracking and not well tested.
Rigid foam can technically be used as exterior sheathing in some areas.
This is not structural and should be checked against local codes. It’s not recommended in most situations because of the lack of structural stability.
It’s preferable to use ridged foam attached to structural sheathing like Zip-R.
Cement board is sometimes used in tropical areas.
Consult with your architect or engineer before choosing an unusual product.
Subflooring is usually plywood, OSB or Avantech (which is a form of OSB). Plywood is generally the best choice for the chemically sensitive.
You can also use solid wood,
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.
You have to spec specific brands that have structural ratings. This is not something that has been in use for long, and it would be unusual to find a good architect who would approve this.
Huber did recently acquire a MgO board company.
Make sure it’s structurally rated.
For those who can’t tolerate wood, it is possible to pour a concrete upper floor, though this is not usually done in North American homes.
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 house wrap. Consider double-sided house wrap tape so that you get more of an air barrier.
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.
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.
Roof Sheathing (Decking)
Plywood, OSB and Huber products are also the most common roof decking.
Purlins or skip sheathing can be used as an alternative 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) says Paula Baker-Laport, Architect.
Huber Avantech products are applied with a polyurethane adhesive. You would want to check for the tolerability of polyurethane adhesives (as well as the Avantech product themselves).
Corinne Segura is a Building Biologist Practitioner with 6 years of experience helping others create healthy homes.
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