What you'll need
Torch-on felt application requires specialist equipment and training. Never attempt hot-works roofing without proper training and fire precautions.
Step-by-step guide
- Find the leak sourceThe water entry point is rarely directly above where water appears inside. On a flat roof, trace water to the highest point it could have entered — check seams, upstands, flashings, and any penetrations (pipes, vents) first.
- Clean and dry the areaScrape away any loose, blistered, or cracked felt. Wire brush back to a clean, stable surface. The repair area must be completely dry — use a heat gun or wait for a dry spell.
- Prime the surfaceApply roofing primer to the clean area and let it tack off (usually 15-30 minutes). Primer is critical — without it, adhesive-backed patches peel within months.
- Apply the patchCut your felt or EPDM patch to extend 150mm beyond the damaged area in all directions. Apply roofing adhesive, lay the patch carefully (no wrinkles), and use a seam roller to press it firmly from centre to edges.
- Seal all edgesApply lap sealant to all four edges of the patch. This is the most common failure point — unsealed patch edges let water under the repair.
- Check drains and outletsA blocked flat roof drain causes ponding that accelerates damage. Clear all outlets and check they're watertight at the collar.
Coat the entire flat roof with liquid waterproofing membrane every 5-7 years. It costs £200-400 in materials and extends the life of the roof by a decade.
Expert tips for the best result
- The best flat roof repairs are done in warm weather (above 10°C) — adhesives don't bond properly in cold conditions
- EPDM (rubber) membrane is far more durable than traditional felt — if you're patching an old felt roof repeatedly, consider a full EPDM overlay
- Ponding water (standing more than 48 hours after rain) needs drainage work, not just patching
- Lead flashings where flat roofs meet walls are the most common leak point — check these before the roof surface itself
- A GRP (fibreglass) flat roof is best repaired with GRP repair kits — standard felt patches won't adhere properly
Useful tools and products
When to call a professional roofer
If the decking (the wooden boards under the felt) is soft or rotten, if there's a large area of failed felt, if the roof has persistent ponding issues requiring drainage work, or if the roof covering is torch-on felt.
We connect you with vetted local roofers across the UK — fast response, free quotes, guaranteed work.
💬 Get a free quote via WhatsAppFrequently asked questions
How difficult is how to fix a leaking flat roof for a beginner?
This guide is rated Moderate. Flat roofs are prone to ponding water and UV degradation. Most leaks come from failed seams, blistered felt, or cracked flashings rather than the flat surface itself. Small repairs to felt and EPDM ru If you're not confident, a professional roofer can do this quickly and provide a guarantee on the work.
How long does how to fix a leaking flat roof take?
Allow 2-4 hours. This assumes the tools and materials are ready before you start. First-timers should budget extra time for preparation and any unexpected issues.
How much does a roofer charge for this in the UK?
Most roofers charge £40-80 per hour depending on location and complexity. For a straightforward job like this, expect 1-2 hours of labour plus materials. Get a fixed quote via WhatsApp — message us with your postcode and job details.
How do I find a reliable roofer near me?
WhatsApp us with your postcode and job description. We match you with a vetted local roofer from our network — most jobs get a response within the hour. Contact us here.