How to Repair Roof Underlayment (Tear, Wind-Lift, or Storm Damage)

Last updated: June 15, 2026

Roof underlayment is the felt or synthetic sheet between your shingles and the wood deck. Most of the time you never see it — but when a storm lifts shingles, a nail backs out, or a tree branch tears a row, the underlayment is exposed and almost always damaged underneath. New shingles laid over torn underlayment leak at the nail holes within a season. The right repair is a self-adhering membrane patch lapped properly over the tear, not just more roofing cement.

When to call a roofer instead of patching: if the damage runs across more than a few square feet, the deck under the underlayment is soft or stained, or the tear is in a valley or around a penetration (chimney, skylight, vent stack). Those locations water-test differently and the cost of a leak below them is high. Patch only when the damage is isolated, the deck is sound, and you can lap onto undamaged underlayment on every side.

Pick the right patch material

• Self-adhering rubberized asphalt (peel-and-stick). What we recommend for any patch — it bonds to the deck, self-seals around nails, and laps cleanly over the existing underlayment. Same product roofers use in valleys and along eaves.
• Synthetic underlayment. Lighter and stronger than felt, but needs cap nails AND a seal at every lap. Fine for a full re-felt of a slope; finicky for a small patch where each fastener becomes a potential leak point.
• 15# or 30# felt. The old standard. Avoid for patches: it tears at fasteners, does not self-seal, and the laps need cement everywhere. Use synthetic or peel-and-stick.

Patch it in this order

1. Strip back enough shingles to work. Lift one full course above and below the damaged underlayment using a flat bar; you only need enough room to slide a patch under the upper shingles. Save the lifted shingles — they go back on top.
2. Cut the damaged section out cleanly. Square edges, not jagged ones — a utility knife and a metal straight-edge. Cut back to undamaged underlayment so your patch has 4+ inches of sound material to bond to on every side.
3. Inspect the deck. Press hard on the exposed plywood. If it gives, is stained dark, or smells damp, the patch is not the fix — you need to replace the sheathing first. Underlayment patched over rotten deck is a callback waiting to happen.
4. Cut a self-adhering patch 4" larger than the hole on every side. Peel the release liner back gradually as you lay it; this material grabs hard the moment it touches the deck. Lap the bottom edge OVER the existing underlayment below the hole, then the sides, then tuck the top edge UNDER the upper underlayment so water sheds shingle-style.
5. Seal the lap edges with roof cement. A 1/4" bead along every cut edge of the patch where it meets the existing underlayment — even on self-adhering material. This is the belt-and-braces step that separates a patch that holds for ten years from one that fails in two.
6. Re-shingle. Slide the saved shingles back into place, re-nail the bottom course, and seal each nail penetration with a dab of roof cement. Use the shingle calculator to size replacement shingles if any were too damaged to reuse. Allow for the standard waste factor on a patch — small areas waste proportionally more.

A properly-lapped peel-and-stick patch on a sound deck has the same expected life as the shingle above it. The failure mode to watch is the lap edge separating in heat — re-seal it with the same cement at the next roof inspection if it lifts.

Related

Working out whether this is a patch or a full slope re-roof? The roof repair vs replace guide walks through the call. If shingles lifted but underlayment is sound, jump to the shingle calculator for the replacement count. New install or full re-felt? Size the rolls against roof area.