Plywood (top) and OSB (bottom) offer a choice typically made on the basis of price, application, and local climate conditions.
Credit: Photos: courtesy Georgia-Pacific Plywood (top) and OSB (bottom) offer a choice typically made on the basis of price, application, and local climate conditions.

There's a soft spot on the roof so that re-roofing will include replacing some sheathing. But with what? Two materials are commonly used, plywood and oriented strandboard, or OSB. Plywood, which consists of cross-layered sheets of veneer glued in place, has been around for a hundred years or longer. OSB, introduced during the 1970s, now has greater market share. Roofers often have strong opinions about which is best, though much depends on local climate conditions and the particular application.

“We only replace deteriorated decking with plywood,” says Jimmy Waller, vice president of development for Waller Construction, in Lakeland, Fla., which includes Goff-Waller Roofing. “We believe plywood is still the best decking material.”

PRICE DIFFERENTIAL Why would a roofing contractor use anything other than plywood? The answer: price. Randy Brown, owner of Clearwater Home Improvement, in Mystic, Conn., says OSB typically costs $7 to $10 per panel less than plywood. So Brown regularly uses OSB to frame houses in his home building business, but on a re-roof where just a few sheets are needed, he sticks to plywood, which more readily absorbs the effects of incidental leaks, and is lighter, thus placing less stress on rafters.

OSB RESPECTABILITY At Builders & Remodelers Inc., in Minneapolis, president and general manager Ken Bressler says he normally leans toward OSB, for price reasons.

“If price had nothing to do with it, I'd say plywood,” Bressler says. “If the [price] difference is 50%, the decision is made” — though he says that on a large job, he would first call supply houses for pricing. “But if it's a small repair, I leave it to the discretion of the foreman,” who can pick and choose based on availability. Bressler points out that OSB has been around so long that it's not viewed as an inferior material and “if the job's done right, moisture is never going to reach that wood surface anyway.”