What Is Roof Decking (Sheathing)?

Decking is usually plywood or oriented strand board in four-by-eight sheets, nailed across the framing with the long edges running perpendicular to the rafters. Older homes may have solid plank decking or spaced boards, called skip sheathing, which suits wood shingles but not asphalt shingles, since the fasteners need solid wood to bite. The deck carries the roof load, resists racking, and holds every shingle nail, so its condition decides how well the roof covering performs.

Nobody knows what is under the shingles until tear-off, which makes decking the classic unknown in a roofing contract. Good proposals state a unit rate for replacing rotted or delaminated sheets and say who approves the extra work. On insurance jobs the adjuster generally pays for decking damaged by the covered event or replaced to meet code, and not for rot from years of slow leaks. Photos taken at tear-off settle most of those arguments.

A decking charge sounds like an upsell to a homeowner unless the rep set it up beforehand. The surprise is the problem: a contract with no unit price invites a dispute the moment a sheet is pulled. Plywood and oriented strand board also behave differently when wet, with strand board edges swelling more readily, and soft or spongy spots underfoot are the sign to look for.