Can you repair roof felt under the shingles, or does it need replacing?
Short answer. Felt underlayment can be patched where it is exposed, such as under missing shingles or during a flashing repair, but it cannot be repaired across a roof without removing the shingles over it. Wrinkled, brittle or rotted felt under a whole roof is replaced during a roof replacement, typically with synthetic underlayment plus self-adhering membrane at valleys, eaves and penetrations.
When patching works
- Localized damage found during a repair: under a missing shingle, around a pipe boot, beside a chimney.
- The patch is lapped correctly, with its top edge under the existing felt above, so water runs onto it rather than behind it.
- The deck below is sound and dry.
Why you cannot fix felt from the inside
Felt sits between the decking and the shingles. From the attic you only see the underside of the decking, and sealing or taping the decking from below does nothing about water already traveling on top of it. Leaks have to be fixed from the roof side.
Signs the felt is failing roof-wide
- Wrinkles telegraphing through the shingles as ripples, common with felt that got wet before shingling.
- Felt that crumbles at the edges when a shingle is lifted, typical of very old roofs.
- Several leaks with no single obvious source.
- Stained decking spread across the attic.
What replacement brings
During a full replacement, the old felt comes off with the shingles. Most roofs today get synthetic underlayment, which is lighter and more tear resistant than felt, plus self-adhering ice and water membrane in valleys, around penetrations and along eaves. Under the 2024 IRC as amended in Georgia, effective January 1, 2026, shingle roofs with a pitch from 2/12 up to 4/12 need two layers of underlayment. See synthetic underlayment vs felt and ice and water shield in Georgia.