What Is an OSB Subfloor?

Manufacturing OSB

• OSB subflooring gets its strength from a manufacturing process that involves layering small strands of wood at right angles to each other. The strands are coated in resin or a similar adhesive and compressed into flat sheets. Additional sealers, applied to all areas of the OSB sheets, help repel moisture.

OSB Properties

• OSB subflooring sells in 4-by-8 sheets of varying thickness. The long sides of the sheets feature tongue-and-groove installation technology, but the shorter ends of the sheets are blunt. OSB subflooring installs on floor joists with standard 16-, 19.2- or 24-inch spacing. Install OSB sheets perpendicular to the direction of the floor joists. This ensures that the short blunt ends will extend to the center of a joist, which is called "breaking on joist." The long tongue-and-groove sides interlock to provide a structurally sound subfloor base.

OSB vs. Plywood Subfloor

• OSB subflooring lays flatter than does plywood subflooring, which tends to bulge and warp when exposed to humidity. In addition, OSB panels typically "seed" easier, meaning they require less force to drive the tongue-and-groove edges of adjacent sheets together. Seeding plywood subflooring sheets often requires a minimum of two workers, one to exert downward pressure on the seam, and the other to drive the new sheet tightly against the previous sheet with a heavy mallet. Seeding OSB subflooring goes quickly with two workers, but one worker can install it if necessary.

Subfloor Cost Comparison

• The cost of OSB subflooring usually is less than the cost of plywood subflooring, although most construction materials are subject to frequent price fluctuations. As of October 2011, a standard sheet of OSB subflooring costs $13.47, and a comparable sheet of plywood subflooring costs $24.25, according to Home Depot. Labor costs to install both types of subflooring are similar.