Enhanced Plywood and Subfloor Products

Plywood vs. OSB

When plywood was developed to replace solid-board sheathing for subfloors and decking, builders were generally reluctant to switch to the new product, which ultimately became the standard for subfloor applications. When OSB came on the scene as an alternative to plywood, detractors were quick to point out its deficiencies. The truth is that plywood and OSB each have strengths and weaknesses when used as exposed decking or subflooring.

When a roofless, partially built structure takes on water, both plywood and oriented strand board (OSB) used for floor decking can absorb water, swell, delaminate, and require sanding or replacement before finish flooring can be installed. The fix is to use water-repellent or water-resistant products in place of ordinary plywood or OSB.

Plywood and OSB are considered “structural panels,” and building codes treat both materials equally. Compositionally they are different, however. Plywood is made from glued strips of wood veneer that are layered at alternating 90 degree angles and placed in a hot press. The resulting cross-laminated and layered material is structurally enhanced and resistant to the expansion and contraction that affects wood.

OSB uses 3-inch to 4-inch strands of wood that are also layered and configured in a crossing pattern, then glued and pressed. OSB is heavier than plywood, absorbs less moisture, and is considered a more structurally consistent product. Furthermore, OSB does not have the delamination issues that can plague plywood. However, OSB is prone to edge swelling when exposed to moisture, and does not dry out as fast as plywood. In addition, a couple of national ceramic tile associations have discouraged the use of OSB as a subfloor or underlayment below a tile or ceramic finished floor, due to the problems encountered by edge swelling. “Wood and water just do not mix well,” says Jeff Key, marketing manager for wood products at Georgia-Pacific. To address these water issues, OSB and plywood manufacturers are refining their products.