Q: What are the concerns about VOC emissions from exterior plywood and OSB?
A: Clayton DeKorne, chief editor of JLC, responds: VOC emissions are pretty much a nonissue for exterior-grade plywood and OSB. Exterior-rated structural panels use moisture-resistant phenolic-formaldehyde resins in the adhesives (this is also true for wood I-joists, LVL, glulams, cross-laminated timber, and many other types of engineered lumber). These adhesives do not off-gas substantially, nor do they add much of anything to the levels of indoor air contaminants.
The emissions from exterior-rated composite wood products are quite different from the off-gassing typically experienced from more volatile urea-formaldehyde resins that bind together interior-rated panels, such as the particle board and MDF used in some cabinetry, as well as laminated flooring. But even that is changing quickly.
Effective June 1, 2018, all composite wood products must meet formaldehyde emissions standards set by the California Air Resource Board (CARB) Air Toxic Control Measure (ATCM) for Composite Wood Products. And effective March 22, 2019, these products must meet a national formaldehyde standard, dubbed TSCA Title VI, put forward by the Environmental Protection Agency, which mirrors the CARB standards.
These standards apply only to hardwood plywood (veneer and composite-core panels), particleboard, medium-density fiberboard (MDF), and thin MDF. Structural engineered wood products manufactured for construction applications, including structural plywood, oriented strand board (OSB), wood I-joists, laminated veneer lumber, and glued-laminated timber, have always been exempt from regulation by both CARB and TSCA because they are made with low-emitting, moisture-resistant adhesives.
It’s worth noting that the new EPA ruling that set formaldehyde limits effective in 2018 and 2019 applies only to the manufacturers of those panels. The regulation is intended to limit products in the supply chain. Installers of the panels cannot be penalized.