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An Overview of Low-VOC and Zero-VOC Sheathing and Subflooring Options
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.” APA Source
While 0.1 ppm is high for someone sensitive, the fact that the panels rapidly offgas should make them tolerable for someone with MCS.
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 pressed wood products.
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 don’t recommend it.
Purebond is made with “soy-based glue” which could mean 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.
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 mold 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. It is not often recommended by building science experts.
Rigid foam can also be used as exterior sheathing. The rate of XPS offgassing is very low, but it does contain a flame retardant. The other option is Polyiso. The Johns Manville brand is popular. 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. 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.
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. I would not move forward with a material like Rewall without approval by an architect.
Consult with your architect or engineer before choosing an unusual product.
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 for me but consult with an architect before using this. You have to spec specific brands that have structural ratings.
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. 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.
Roof Sheathing (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). (Source Paula Baker-Laport, Architect).
Corinne Segura is a Building Biologist with 6 years of experience helping others create healthy homes.
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