Roof Decking Replacement

Decking, usually plywood or OSB, is the structural surface that spans the rafters or trusses and gives every other layer — underlayment, starter strip, shingles, flashing — something solid to attach to. It's not visible once a roof is finished, which is exactly why problems with it tend to go unnoticed until they're serious.

Long-term, unaddressed leaks are the most common cause — water finding its way in slowly through failed flashing or aging shingles, saturating the wood underneath over months or years rather than all at once. Poor attic ventilation contributes in a quieter way, trapping moisture against the underside of the deck even without an active leak. Roofing over an old layer instead of tearing off can also hide decking problems for years, since nobody actually looks underneath the old material until it finally comes off.

Tear-off is the point where decking condition actually becomes visible, which is one of the reasons we don't roof over an existing layer. Once the old shingles and underlayment are off, we walk the entire deck checking for soft spots, delamination, staining or any area that flexes underfoot, and photograph anything we find before repair begins. Occasionally a decking issue is visible from inside the attic beforehand — staining, sagging, or daylight showing through — which we'll flag during a free inspection if attic access is available.

Small, isolated soft spots are typically cut out and replaced with matching material, tied into the surrounding structure so the new panel sits flush with what's around it. Widespread rot or sagging across large sections points toward replacing the deck more broadly rather than patching piece by piece, since a roof is only as reliable as its weakest section of decking. Either way, no new roofing material goes down until the deck underneath it is sound.

Manufacturer warranties generally assume a sound, properly prepared deck underneath the shingles, and installing over rotted or compromised decking is a fast way to void that coverage regardless of how well the shingles themselves go on. See our Owens Corning Warranty Guide for more on what keeps coverage intact, and Our Roofing Process for where decking inspection fits into a full project.