Exterior sheathing in wood frame construction is attached to the outside of the frame and makes up the surface to which the exterior finish is applied. Before manufactured sheet goods such as plywood were available, ix or 2x material was nailed to the studs for this purpose. In standard wood frame construction today, exterior-grade plywood or OSB (oriented strand board, also known as wafer — board) is typically used as exterior sheathing for the entire building or at corners where shear strength is required. These materials contain varying degrees of formaldehyde and isocyanates and do not have the longevity of solid wood products.
Many problems with the use of OSB in roof and wall sheathing have recently been identified. In fact, one prominent manufacturer was the subject of a class action suit. When the board gets wet it is vulnerable to fungal invasion and rapidly deteriorates. Asphalt — impregnated fiberboard or asphalt-sheathed insulating board is commonly used as infill between the corner shear panels. Since asphalt
is a known carcinogen, we believe that any exposure level is too high when other alternatives exist.
When an air barrier or airtight drywall assembly is used on the interior face of a wall, sheathing material will not have as great an impact on the indoor air quality as the materials exposed to the interior. Moreover, the sheathing will have had several weeks in place to air out before it is covered up. In a permeable or breathing wall system, where vapor barriers are eliminated with the intent of allowing vapor movement through the wall, the type of exterior sheathing must be more carefully considered in terms of both permeability and harmful chemical content. The following maybe included in your specifications to reduce the pollution generated by exterior sheathing: [9]
• non-odorous foam boards such as bead board
• AdvanTech: very low emissions, durable composite wood sheathing for walls, floors and roof
