How to repair a felt roof with tape
A felt roof on a shed, garage or extension usually fails in small ways long before it needs replacing: a split along a lap, a nail hole that's started to drip, a blister that's cracked, or an edge that's lifted in the wind. You can seal most of these yourself in under an hour with a self-adhesive repair tape like Supraseal®, with no torch, no hot bitumen and no mess.
Repair or re-felt?
Tape is the right fix when the felt is mostly sound and the damage is local. If the felt is brittle and cracking all over, the deck underneath is soft or rotten, or water is coming through in lots of places, the roof needs re-felting, and taping it will only buy you time.
Good candidates for a tape repair:
- Splits and tears, including along laps and joints
- Nail and screw holes
- Cracked blisters (cut and flatten the blister first)
- Lifted or leaking laps between sheets
- Leaks at the drip edge, verge or where the roof meets a wall
- Leaks around vent pipes and other penetrations
What you'll need
- Supraseal® Weatherproofing Tape: 100mm for splits, laps and nail holes, 200mm for larger tears and wall junctions (see our width guide)
- A silicone seam roller
- A stiff brush and a clean, dry cloth
- A sharp knife or scissors
Watch the technique
Step 1: Find the leak
Water runs down the slope and along the deck before it drips, so the hole is often higher up than the wet patch inside. Look for splits, lifted laps and nail heads on and above the area of the drip, and mark everything you find.
Step 2: Wait for a dry day and clean the felt
The felt must be completely dry. Brush off moss, leaves, dirt and loose mineral granules from an area wider than the tape, then wipe it down. A clean, dry, firm surface is what makes the repair last. Tape won't bond to loose granules or dust.
Step 3: Prepare the damage
- Blisters: cut a cross through the blister, let it dry out, then press the flaps flat.
- Lifted edges and laps: press them back down so the tape bridges a flat surface.
- Raised nails: knock them flush before taping over.
Step 4: Cut and apply the tape
Cut the tape long enough to overlap at least 50mm beyond the damage on every side, and round the corners so they don't catch and lift. Peel back the liner a little at a time and press the tape down from the centre outwards, without stretching it. Run the tape down the slope, so water flows over the edge of the tape, not into it.
Step 5: Roll it hard
Roll the whole repair firmly, paying most attention to the edges. Rolling is what pushes the butyl into the texture of the felt and starts the bond, which keeps strengthening over time. On a cold day, keep the roll somewhere warm before you start, as the tape is easier to work when it's not cold.
Step 6: Finish edges and walls
At the drip edge or verge, fold the tape over the edge and onto the fascia or batten. Where the roof meets a wall, use 200mm tape and turn it up the wall by at least 75mm (see our guide to upstands and abutments). Supraseal® can be painted once it's applied if you want it to blend in.
Why use a butyl tape on felt?
Supraseal® is butyl based, so it stays flexible through hot summers and cold winters (-30°C to +80°C), it's UV stable for exposed use, and it bonds to bitumen felt as well as timber, masonry and metal around the roof. It's backed by a 10-year warranty.