Leaking flat roof? Professional repair and replacement across West London. GRP fibreglass, EPDM rubber. From £150 patch to full replacement. 0203 302 2547.
In over 20 years of flat roof work across West London, we see the same three failure modes repeatedly. Understanding which one is causing your leak determines whether you need a patch repair or a full replacement.
The most common cause. Flat roofs are never truly flat — they need a minimum 1:40 fall to drain water toward outlets. Many flat roofs on West London extensions, garages and outbuildings were built with inadequate falls. Water pools, UV radiation breaks down the membrane where it ponds, and a leak develops at the weakest point. Once ponding has degraded the membrane, the only lasting fix is replacement with tapered insulation that creates correct drainage.
Where the flat roof meets a wall, parapet or upstand, the membrane must turn upward and be sealed to the vertical surface. This junction is the second most common failure point. Thermal movement, settlement and poor original detailing cause the seal to break, allowing water behind the membrane. Repair is possible if the membrane itself is sound — the junction is re-detailed with new membrane and sealant.
Flat roof outlets collect debris — leaves, moss, bird nesting material, general dirt. When an outlet blocks, water backs up and finds alternative paths through any weakness in the membrane. Regular outlet clearance prevents this entirely. If your flat roof leaks only in heavy rain, a blocked outlet is the likely cause.
If the membrane is sound overall and the leak is at a single identifiable point — a split, a failed junction, a puncture — patch repair is cost-effective at £150–£400. If the membrane is blistered, cracked, or ponding across more than 20% of its area, full replacement in GRP or EPDM is the only lasting solution.
GRP creates a seamless, rigid surface with no joints to fail. It handles foot traffic, resists UV and impact, and lasts 30–40 years. A typical extension flat roof in West London costs £1,200–£3,000 to replace in GRP including tapered insulation, upstand detailing and outlet connection. This is our recommended system for most West London properties.
EPDM is a single-piece rubber membrane that accommodates structural movement — ideal for roofs on older buildings where the deck flexes. It lasts 25–30 years and costs slightly less than GRP at £1,000–£2,500 for a typical extension. Seam-free installation in single sheets up to 15m wide eliminates the joint failures that plagued older multi-sheet systems.
Flat roof leaks are concentrated in specific property types across West London. The 1960s maisonette blocks in Hayes, Feltham and Northolt have original asphalt flat roofs now 50–60 years past design life. Victorian and Edwardian houses across Fulham, Kilburn and Ealing have flat-roofed rear extensions added in the 1970s–80s with felt coverings now failing. Modern apartments in Brentford, Wembley and North Acton have flat roof terraces where developer-grade detailing is failing within 5–10 years of construction.
Every flat roof quote starts with an inspection of the existing membrane, deck condition and drainage. We strip a small test area if needed to assess the deck timber beneath. You receive an itemised quote covering strip, deck repair, insulation, membrane, upstands, outlets and waste disposal. Call 0203 302 2547.
BS 6229:2018 specifies that flat roofs must achieve a minimum finished fall of 1:40 to prevent ponding — standing water that degrades the membrane and causes leaks. Many flat roofs built before this standard have inadequate falls, and the only lasting solution is tapered insulation that creates correct drainage.
Source: BS 6229:2018
"Emergency tarp-up after the January storms — they were here within 3 hours and made everything safe. Permanent repair done the following week."
"Water coming through the bedroom ceiling at midnight. Called and a real person answered. They were out first thing and stopped the leak before breakfast."
"Flat roof on our extension failed after heavy rain. Fast response, honest quote, GRP replacement done in two days. No more leaks."
Patch repairs cost £150–£400. Full GRP replacement costs £1,200–£3,000 for a typical extension. EPDM costs £1,000–£2,500. Call 0203 302 2547 for a free quote.
Yes, if the membrane is sound overall and the leak is at a single point. If more than 20% of the membrane is compromised, full replacement is more cost-effective.
Yes — GRP lasts 30–40 years versus 10–15 for felt. The upfront cost premium is recovered many times over in lifespan.
The three most common causes are ponding from inadequate falls, failed upstand junctions, and blocked outlets. Repeated patch repairs without addressing the root cause will keep failing.
A typical extension flat roof takes 1–2 days. Larger projects or those requiring deck repairs take 2–4 days.
Under current Building Regulations, any flat roof replacement must include insulation to 0.18 W/m²K. Tapered insulation boards also create correct drainage falls.
Yes — GRP is rigid and handles regular foot traffic. It is ideal for balconies, terraces and areas where you need to access equipment or washing lines.
No call-out fee. No obligation. We make your roof safe first.
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