Roofing materials need a sound substrate. Damaged sheathing can affect attachment, drainage and the reliability of the finished roof.
How Decking Becomes Damaged
Common causes include long-term leakage, failed flashing, trapped moisture, impact and deterioration around penetrations or roof edges.
Signs of Possible Deck Damage
Soft areas, visible sagging, repeated leaks, deteriorated attic-side sheathing and damage exposed during tear-off can indicate a substrate problem. See roof leak repair.
Why the Full Extent May Be Hidden
Existing roofing can conceal localized deterioration. Replacement proposals should explain how unforeseen decking replacement will be documented and priced.
Permit Considerations
Changing or replacing sheathing can affect permit requirements in some local jurisdictions. For example, Bellevue specifically identifies roofing work involving sheathing changes within its permit guidance. Requirements should always be checked for the project address. See roofing permit guidance.