Rotted Sheathing Under a Leak
A leak that has been running for a season or two has been soaking the plywood underneath the whole time. That deck is what your roof is nailed to, and soft plywood does not hold a nail.
How common this is here
Roughly 37% of permitted Sacramento County re-roofs from 2023 to 2025 also involved sheathing, dry rot or structural work. On a roof with a known leak, the odds are considerably higher than that.
It is not a sign you were targeted by a contractor. It is the normal consequence of water reaching wood.
Why it cannot be covered over
- Every fastener holding the repair or the new roof anchors into the deck
- Soft plywood does not hold a nail, so the work above it is not secured
- An inspector will look for it on a permitted job
- Manufacturer warranties generally do not cover a system installed over an unsound deck
How it should be priced
Per sheet, at a rate agreed before the roof is opened, with photographs of every sheet replaced. That way the cost tracks exactly how many sheets were actually bad.
A number that appears for the first time while your roof is open, with no photographs offered, is not how a documented allowance behaves.
Where it is usually found
- Around plumbing vents and other penetrations
- In valleys, which concentrate water
- Behind chimneys, where water piles against the masonry
- At the eaves, where gutters have overflowed
- Under any area with a long-standing ceiling stain below it
Common questions
How do I know the sheathing was really replaced?
Photographs of each sheet, taken during the work. Ask for them as a condition of approving the extra cost — any contractor doing this properly already has them.
Can a leak be repaired without replacing the rotted deck?
Not properly. The repair fastens into the deck, and soft plywood will not hold it. Skipping that is how the same leak comes back.