How can you tell if a roof is bad, including the roof decking?
Short answer. A bad roof shows widespread granule loss, curling or cracked shingles, repeated leaks and daylight in the attic. Bad decking shows up as sagging between rafters, soft or bouncy spots underfoot, dark or delaminated sheathing in the attic, and rusted nails.
Signs in the shingles
- Bald patches where the black mat shows, and heavy granules in gutters.
- Curling, cupping or cracking across many shingles, not one or two.
- Missing tabs after ordinary storms, a sign the seal strips have aged out.
- Repeated leaks in different spots, which means the system, not a single part, is failing.
Signs the decking is bad
- Sagging or wavy lines between rafters when you sight along the roof from the yard.
- Soft, spongy spots a roofer feels while walking.
- In the attic: dark staining, mold, sheathing layers peeling apart (delamination), or a nail you can push through.
- Rusty nail tips and frost or condensation marks, which point to ventilation trouble that rots wood from below.
What usually causes bad decking
Long running leaks at flashing or pipe boots, poor attic ventilation trapping moist air, and bathroom fans venting into the attic. OSB is especially sensitive to repeated wetting; see OSB vs plywood decking.
What it means for cost
Bad decking is replaced sheet by sheet during a reroof, so estimates usually list a per sheet price for any rotten wood found after tear off. A roof with failing shingles but sound decking is a normal replacement. Compare your findings with signs you need a new roof.