Question answered
Emergency flat roof leak: what can be done
The short answer
An emergency flat roof leak can be held with a temporary patch while the cause is traced. The patch depends on the membrane: felt, EPDM and GRP each take a different material. Standing water, known as ponding, is often part of the story. A patch buys time, and the lasting repair follows when the surface is dry enough to inspect.
A flat roof that leaks in rain can usually be held quickly, but the right temporary patch depends on the membrane and on where the water is gathering.
First, keep water moving off the surface
No flat roof is truly level. It is built with a fall, a gentle slope towards the outlets, so that rain drains away. IKO, citing the 2018 edition of BS 6229 (since revised), gives a recommended minimum fall of 1:80 on the finished roof, and a design fall of 1:40 so that sagging and building tolerances cannot eat the margin. A roof that finishes flatter than that keeps its water longer than it should.
Ponding means puddles still lying a day or two after rain. They keep constant pressure on seams and joints, and the weight of a deep puddle can also push down on the deck. In an emergency the first job is often to clear a blocked outlet, or the leaves and grit around it, so the water can leave. That costs nothing and sometimes stops the drip.
Do not step onto a wet flat roof to look. The surface is slippery and a weakened deck may give way. Look from a window or the ground for pooled water, torn edges and anything lifting at the walls.
Temporary patches by membrane type
The membrane is the waterproof skin over the deck. Three types dominate on homes here. Felt, including torch-on, is bitumen based. EPDM is one sheet of synthetic rubber. GRP is glass-reinforced plastic: fibreglass matting laid wet and cured hard.
A felt roof can be patched with a bitumen repair piece once the area is dry. EPDM wants a compatible rubber repair tape or patch, applied to a cleaned surface, because the wrong adhesive simply will not grip. GRP is mended with resin and matting, which needs dry conditions and mild temperatures to cure.
That is why emergency work in rain is so often a holding measure. A plain sheet weighted at the edges may be all that is possible until the weather clears. Sealant smeared over a split can trap water beneath it, so we treat it as a stopgap and nothing more. Our guide to temporary roof repairs goes through the general options, and the main emergency roof repairs page shows where this fits.
Where the water usually comes in
On a flat roof the ceiling stain is seldom under the hole. Water travels along the deck or through insulation before it drops. The usual entry points are the upstand (the short vertical lip against a wall), the edge trim, the outlet, a rooflight kerb and the seams between sheets.
A tear in the middle of an open area is rarer than failure at these details. Felt lifts at its laps as it ages. An EPDM sheet is more often let down at its glued edges and corners than across the field of the sheet. GRP can craze or crack at the joint between boards if the deck beneath moves.
We trace from inside first, following the wet line in the ceiling and any darkened timber, then match it to the surface. Working that way finds the true opening, instead of patching the visible stain and returning in a fortnight.
The photographs we take on the survey show each of these points on your own roof.
Patch or replace: how to tell
A patch is enough when the membrane is basically sound and a single local fault has opened. Typical UK guides put a flat roof's life at 15 to 30 years (MyBuilder, updated 21 August 2026), with EPDM at 20 to 30 years or more and a well laid felt roof at up to 20.
If the surface is blistered, split in several places or ponding across most of its area, further patches tend to fail. Wet insulation or a soft deck beneath means the covering is only one part of the problem. In those cases replacing the covering, and perhaps the boards, is the right job. We say which applies and why, and we show you the photographs.
On cost, MyBuilder's flat roof guide lists £45 to £100 per square metre for the covering, as a typical UK range. Access and the condition of the deck both shift the figure, so the best guide for your roof is the quote you receive once it has been surveyed.
Storm, snow and insurance considerations
If a storm opened the roof, tell your insurer promptly and photograph the damage before any cover goes on. Our pages on chimney damage in a storm and snow damage to roofs describe what each event tends to do. A leak caused by a membrane worn out over many years may be treated as age rather than weather, and a refusal can be challenged, as set out in what to do when a roof claim is rejected.
On a listed home, even emergency work may need consent once it goes beyond a temporary measure. Ask the council's conservation team before anything permanent is fixed to the roof.
Keep a note of every date: when the leak began, what rain fell, when you called and what was done. It makes any later conversation with an insurer far easier.
Flat roof leaks: two further questions
Can I put a tarpaulin over a leaking flat roof myself?
Only from a safe position, and flat roofs are often reached by ladder. A sheet can lift in wind and cause more harm, so it needs fixing along a firm edge. Nothing here is worth a fall. If you cannot reach it safely, put a bucket under the drip inside and call a roofer.
Why does my flat roof leak only after several days of rain?
Water can sit in the insulation or deck, then show at the ceiling later. A small gap at a seam or upstand lets in a little each time, and the build-up takes days to emerge. Tracing back from the ceiling stain through the layers is how the real opening is found.
Tell us about your roof
Describe what is happening and we will call you back to arrange a visit.
- Photographs of what we find
- A written quote with one total price
- Or call 01903 299063
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