Garage Roof Leaking

What's happening?

Garage roofs fall into a few types and each leaks in its own way. A low-pitched roof of felt on boards leaks at laps, splits and the edge. A corrugated metal or plastic roof leaks at fixings, laps and where sheets have moved. A corrugated cement roof, common on garages built before 2000, cracks and slips, and many were made with asbestos. Asbestos cement is only a risk to health when the fibres are released by breaking, drilling, scrubbing or pressure washing, but those are exactly the things people do to a leaking roof. The roof is also usually shallow, so water sits at laps and edges, and condensation on an uninsulated underside can look like a leak. Find out which type you have, then which fault.

What usually causes it?

• A split, lifted lap or worn felt on a flat or low-pitched garage roof
• Cracked, slipped or weathered cement sheets, or failed fixings
• Poor or missing flashing where the garage meets the house or a wall
• Too low a pitch for the covering, so water backs up at the laps
• A blocked or damaged gutter spilling water down the wall
• Condensation dripping from the underside of a cold metal or cement roof

Is it dangerous?

Mainly because of what the roof might be. Breaking, drilling, scrubbing, power washing or sawing asbestos cement releases fibres, and no amount of asbestos is safe to breathe. HSE says work on asbestos cement can be done without a licence if workers are trained and the work is assessed, so a competent contractor, not a DIY job, is the right route for a damaged or old sheet roof. Otherwise the damage is to what you store inside.

Can I fix it myself?

Look from the ground and from inside the garage. Photograph the roof, note where water enters and whether it drips only in rain or also in cold, damp weather. If the garage is older than about 2000 and the sheets are corrugated and grey, treat them as asbestos until proved otherwise: do not break, drill, brush, scrape, paint or pressure wash them. Move belongings under the leak and keep the gutters clear.

When should you call a roofer?

Call a roofer to repair or replace a felt, metal or GRP garage roof. For a grey corrugated sheet roof of unknown age, ask for the material to be identified before any work starts, and use a contractor who is competent on asbestos cement. If you rent the garage, tell the landlord in writing.

What will the roofer actually do?

• Identify the roof type and, for old sheets, arrange a sample or survey before touching it
• Find the entry point by inspecting laps, fixings, edges and junctions
• Repair or replace the felt, sheet or flashing, or re-cover the roof
• Fit new flashings where the garage meets a wall and check the pitch suits the covering
• Clear and repair the gutters and downpipe
• Safely remove and dispose of asbestos cement sheets where they have to come off

Who fixes this

• Roof leak repair
• Flat roof repair

Questions people ask

Sources & References

1. HSE: asbestos FAQs
2. HSE: asbestos
3. Designing Buildings: flat roof
4. NFRC: choosing a roofing contractor