Indoor Air Quality Often Tied to Building Products: OSB vs Plywood

How does moisture affect the performance of each of these building products and how can that moisture affect you and the quality of the air that you breathe?

A big difference between OSB and plywood buildingn products is that one holds moisture and one does not.  Why should you care?  Moisture in the product is conducive to fungus growth, i.e. mold.  That mold and its spores produce mycotoxins that can affect your health. 

Usually these building products, OSB and plywood, are used on roofs, walls and subfloors.  Areas we cannot easily see.  If the product is wet, swelling and deterioration is not visible.  A big performance difference between plywood and OSB is the moisture factor.  Both are engineered products.  Both meet or exceed performance standards for strength, stiffness, dimensional stability and bond durability.

However, plywood dries faster and does not deteriorate with repeated exposures to water or moisture.  In fact, moisture drains through a plywood panel.  OSB, in comparison, holds moisture.  Studies show that repeated cycles of wetting and drying significantly compromised OSB’s ability to resist water infiltration with each subsequent cycle.  That moisture is conducive to mold growth.   In addition, the glue which holds the word chips together in OSB becomes a food source for mold spores already present. 

Another difference between the two building products is swelling.  The increased moisture content in OSB will cause the product to swell.  Product testing revealed that OSB could swell as much as 30% compared to plywood’s 9%, as the illustration on this page illustrates. 

When deciding whether OSB is a reasonable substitute for plywood on any particular project these attributes should be considered.  For many uses OSB provides performance or service values that are superior to plywood.  However, it is clear that risk factors, such as moisture should be considered.