What is roof decking?

Roof decking is the platform of plywood or oriented strand board (OSB) that forms the base layer of your roof. It fastens directly to the roof trusses and provides the solid surface where roofers attach shingles, metal panels, or other covering materials. This structural layer is essential: without it, roofing materials have nothing to hold them in place.

Decking typically comes in half-inch to three-quarter-inch thickness and is installed in sections across your roof frame. In older Georgia homes, you may find solid board decking or even skip sheathing (boards with gaps between them), but most modern roofs use plywood or OSB for its strength and affordability.

Roof decking fails when water gets underneath the shingles and causes the wood to rot, warp, or delaminate (separate into layers). You may notice soft spots when climbing into your attic, sagging areas visible from outside, or a spongy feel underfoot on the roof itself. Severe damage allows the decking to break down completely, which can lead to structural problems in your roof frame and ceiling.

If decking is damaged in localized areas, a roofer can sometimes replace just those sections. Full decking replacement becomes necessary when rot is widespread or when the decking is too compromised to support new shingles securely. This work is often discovered during roof replacement inspections when the old covering is removed and the deck is fully exposed.