How to fix roofing felt

Roofing felt fails for simple reasons. Laps lift, corners get scuffed, blisters pop, water creeps in. The good news is most small faults are easy to sort with cold-applied products that do not need a flame. This guide shows you how to diagnose the leak, pick the right fix, do the job safely, then check your work. If the problem is bigger than a patch, you will know it and you will know when to call a roofer.

Safety first on any roof

Working at height can go wrong fast. Keep it short and controlled.

Ladder and access basics Pick a ladder that reaches at least one metre above your step-off point. Set it on firm, level ground at the 75 degree rule. Keep three points of contact. Do short tasks from ladders only, move the ladder often, never overreach. For pitched roofs use a roof ladder with a ridge hook. For flat roofs, use a safe access point and stable footing. Gloves and eye protection are not optional.

Why DIY should avoid hot works Torch-on felt and open flames are a fire risk and often need a hot work permit in managed settings. Home repairs are safer with cold-applied bitumen, tapes, and liquid compounds. If a method mentions a flame or heat source, park it and bring in a pro.

Diagnose the problem before you patch

Jumping straight to a patch can miss the real cause.

Common felt failures

• Tears at edges and corners

• Lifted laps that let capillary water track inside

• Pinholes or cracks in mineral finish

• Blisters from trapped moisture

• Failed flashings where the roof meets a wall or pipe

• Ponding that sits after rain and magnifies small faults

  
  

Quick checks 

Go inside first. Track stains and drips back to likely roof areas. Outside, sweep leaves, clear outlets, and look for standing water. Inspect perimeters, upstands, and the lowest points. Many leaks start at a lifted edge.

Repair or re-felt

Use this rule of thumb.

• Damage smaller than a postcard, with sound felt around it, patch it

• One strip of shed felt torn or brittle, re-felt that side

• Soft deck, widespread blisters, failed falls, or complex junctions, call a roofer

  
  

Tools and materials you will need

• Ladder, roof ladder if pitched, gloves, eye protection

• Stiff brush, scraper, roller, utility knife with hooked blades

• Tape measure, chalk line, clean rags

• Cold-applied bitumen adhesive or liquid bitumen repair compound

• Mineral felt repair patches or felt offcuts

• Reinforcing scrim or repair tape

• Bitumen primer if the surface is dusty or porous

• Compatible edge sealant

• For sheds, clout nails or felt nails, timber battens if needed

  
  

Weather rules Pick a dry day, above 5°C, with no rain on the way. Avoid frost, heavy dew, or strong winds. Follow curing times on the tin.

Quick steps to fix roofing felt

Pick a dry day. Brush off dirt and cut out loose felt. Prime if needed. Spread cold-applied bitumen beyond the damage, then lay a felt patch with 75 to 100 mm overlap on all sides. Bed reinforcing scrim if using liquids. Top coat, roll firm, seal the edges, then check again after 24 to 48 hours.

Patch a small tear or puncture on a flat felt roof

A neat, layered patch lasts longest and looks tidy.

1) Prepare Brush the area clean. Chalk out a rectangle that covers the damage with at least 100 mm all round. Cut the damaged felt neatly. Feather the mineral surface at the patch perimeter with a scraper so the new patch sits flush. Let the surface dry fully.

2) Prime and bond If the felt is dusty or porous, paint a thin bitumen primer and let it flash off until tacky, not wet. Spread cold-applied bitumen adhesive across and beyond the cut-out by 25 to 50 mm.

3) First patch Cut Patch A so it overlaps the cut-out by 75 to 100 mm on every side. Lay it into the wet adhesive. Roll with firm pressure from the centre out to chase out air. Wipe away any bleed.

4) Reinforce For belt and braces, embed a strip of scrim over the repair, set into a thin coat of adhesive or liquid. This handles movement.

5) Second patch Cut Patch B 25 to 50 mm bigger than Patch A on all sides. Rotate it so laps do not line up with Patch A. Bed it in more adhesive. Roll again. Seal the edges with a compatible bitumen mastic.

6) Cure and test Leave it to cure as per the product instructions. After 24 to 48 hours, check for full adhesion. If allowed, a light hose test helps prove the seal. Do not walk on fresh repairs until cured.

Re-felting a shed roof the right way

If a large section of shed felt is split or brittle, strip and relay rather than chase leaks all winter.

1) Strip and inspect Remove ridge capping and barge trims. Prize up felt nails and lift the old felt. Bag waste to keep fibres down. Check the roof boards. Replace any soft or rotten timber. Let boards dry before covering.

2) Measure and cut Most sheds take two or three strips laid from eaves to eaves with a ridge overlap. Measure length with 50 to 75 mm overhang for drips. Cut strips on the ground.

3) Lay the first strip Brush boards clean. Starting at the low eaves, bed the first strip in cold-applied adhesive or fix with felt nails every 150 mm along edges and at 300 mm centres in the field. Keep it straight with a chalk line. Leave 50 to 75 mm for the side lap.

4) Lay the second strip Overlap the first by 50 to 75 mm. Bed the lap in adhesive for a watertight joint. Nail as above. If the shed is wide, repeat for a third strip.

5) Ridge and edges Fold the felt down the eaves for a neat drip and fix under the fascia. At the gables, trim flush, then fit barge boards or a timber batten and cap with a separate ridge piece that overlaps each side by at least 150 mm. Bed the ridge in adhesive and nail at the top only. Seal exposed edges.

6) Finishing touches Press all laps with a roller or block of timber. Wipe bitumen squeeze-out while soft. Refix trims and paint them to shed colour. Tidy the site.

Fixing lifted laps and edge details

Lifted lap Dry the joint. Gently lift the loose felt. Brush out dust. Prime if needed. Butter both faces with cold adhesive. Press and roll. Weight the area for an hour with a board and bricks. Seal the edge with mastic.

Drips, upstands, and flashings At metal drips or timber edges, reseal with compatible tape or mastic. For upstands where the roof meets a wall, check the flashing. If the metal is sound but the seal is cracked, rake out the joint carefully and reseal with a roofing-grade sealant. If the flashing has come loose, that is a job for a roofer.

Blisters, ponding, and recurring leaks

Blisters If a blister is dry, stable, and not leaking, you can often leave it. If it is soft or splits under light pressure, cross-cut the top, lift the flaps, dry the area, butter with adhesive, press flat, then patch with the two-layer method. Large fields of blistering point to trapped moisture in the system and need a pro.

Ponding water Flat roofs should still have a fall. Clear outlets first. Minor low spots on a shed can sometimes be eased with a thin tapered board under the felt at the next re-felt. Persistent ponding on a home roof needs a roofer to correct the falls or add crickets.

Product chooser for small DIY felt repairs

• Cold-applied bitumen adhesive Best for bedding patches and laps. Easy to spread, strong final bond.

• Liquid bitumen repair compound Brush or trowel on, useful for sealing hairline cracks and embedded scrim.

• Reinforcing scrim or tape Adds strength over cracks or joints before a top coat.

• Mineral felt patches Cut from matching felt for tidy, durable repairs.

• Compatible sealant For edge dressing and small detail seals. Check the label for compatibility with bitumen.

  
  

Always choose products that are marked as compatible with bituminous felt. Do not mix systems unless the manufacturer says it is allowed.

Weather, timing, and aftercare

Plan the job for a dry window. Cold weather slows curing. If you must work in cooler conditions, keep materials warm and avoid late afternoon when dew forms. Do not trap damp under a patch. After the first heavy rain, check your work. Clear leaves each autumn, keep outlets open, and look over edges and laps twice a year. Small maintenance stops big leaks.

When to call a roofer

• The roof deck feels soft underfoot

• Blisters or cracks cover large areas

• There are complex junctions with parapets, skylights, or abutments

• The existing system is torch-on or multi-layer and you are not trained

• Leaks keep returning after patching

  
  

A roofer can survey the falls, check hidden damage, and give a warranty on a system fix.

FAQs

How long does a felt patch last 

A tidy, two-layer patch with scrim can last several years if the surrounding felt is sound. Keep the area clean and check it each season.

Can I repair felt in winter 

Yes, if it is dry and above about 5°C, but curing takes longer. Avoid frost or heavy dew. Warm materials indoors before you start.

Is torch-on better than cold-applied 

Torch-on is great in skilled hands but not for DIY. Cold-applied products are safer and more than good enough for small repairs.

What overlap should I use on a shed roof 

Aim for 50 to 75 mm on side laps and at least 150 mm at the ridge. Bed laps in adhesive for a watertight seal.

Do I need underlay beneath new shed felt 

Most garden sheds use a single mineral felt layer. Heavier use or exposed sites benefit from an underlay plus a mineral cap sheet. Check your shed maker’s guidance.

Why does my roof blister 

Moisture trapped under the felt turns to vapour on warm days and lifts the layer. Small stable blisters can be left. Soft or splitting blisters should be cut, rebonded, and patched.

How do I seal a lifted flashing 

If the metal is fine, rake out old mortar or sealant and apply a fresh bead of a compatible roofing sealant. If the metal is loose or corroded, call a roofer.

Can I walk on a flat felt roof 

Light foot traffic is fine on cured felt with care. Use soft-soled shoes, spread your weight, and avoid fresh patches.

Short summary

Most felt roof leaks come from small faults you can fix with cold-applied adhesive, a tidy patch, and good prep. Work safely, repair on a dry day, and check laps, edges, and outlets. If you spot a soft deck, big blisters, or complex details, bring in a roofer.

Key takeaways

• Diagnose first, patch only sound areas

• Use cold-applied products, not flames

• Overlap patches by 75 to 100 mm and roll them tight

• Re-felt sheds in strips with clean laps and a 150 mm ridge cap

• Keep outlets clear and check again after the first rain