The short answer
Keep off the roof if it is wet or you cannot reach it safely. From inside, catch the water and protect the ceiling. A roofer can fit a temporary patch of sealant, a bitumen patch or a sheet held down at the edges until the proper repair is done. Anything stuck on with the wrong product can make the final repair harder, so photograph the roof first.
Why flat roofs leak differently
A pitched roof sheds water quickly. A flat roof carries a slight slope that steers water gently to an outlet, and its covering must stay sealed across the full surface. Standing water does not cause a leak by itself, but it finds any weakness: a split along a seam, a blistered patch of felt, a lifted edge, a cracked upstand or a blocked outlet.
The drip you see on the ceiling is often a long way from the hole, because water travels along the deck or the joists before it comes through. That is why guesses from inside the house rarely find the right spot. Flat roofs are covered in felt, EPDM, GRP or lead, and each material fails in a different manner, so the first step is knowing which one you have.
What you can safely do from inside
Place a bucket under the drip with a plastic sheet beneath it. If the ceiling is bulging, follow the steps on our page about a ceiling bulging with water. Shift furniture away, and if a light fitting is wet, turn that circuit off only where the route to the fuse board is dry.
Resist the urge to poke at the ceiling. A damp patch that is holding is better left alone, and a bulge needs the careful release described on that page. Mark the edge of the stain with a pencil and add the time, so that you can see whether it grows overnight.
Which covering is on the roof
The right patch depends on the surface, so work out what you have. Felt is black, slightly gritty and often shows blisters or cracks. EPDM is a smooth rubber sheet, usually with few seams. GRP is a hard, glossy fibreglass shell. Lead is grey, heavy and creased at the joints. Many small garage, dormer and extension roofs are felt or GRP.
Tell us which you think it is, and send a photograph taken from a window or the ground, never from the roof itself. If the roof is old or has been patched before, say so, because earlier repairs can limit what will stick.
Look into the loft or ceiling void if there is access, without leaning on wet plasterboard. A torch will show damp timber or a trail of water. Take photographs of the stain and of anything you see above it. They help the roofer, and they help if you later decide to make an insurance claim.
Temporary patches that suit a flat roof
A roofer can work out what has failed and fit a temporary measure that suits the covering. On felt, a patch of bitumen-based repair material bedded over a dried, cleaned area can hold for a short spell. On EPDM, a cold-applied adhesive patch made for rubber membranes is the usual choice. On GRP, a resin repair with glass-fibre cloth works if the area can be dried. A sheet of heavy-duty polythene or tarpaulin can cover a larger area, held down along the edges and weighted.
None of these is a final repair. The point is to stop water getting in until the weather and the access allow proper work. Our page on gutter or roof leak helps if it is unclear where the water is coming from, since an overflowing outlet can look like a hole in the roof.
What to avoid
Avoid spreading general-purpose sealant over a wet roof, because it will not stick and it hides the original fault. Do not use roofing cement on a membrane it is not made for, and do not nail a sheet through the covering, as every nail is a new hole. Stay off the roof in wind or rain, and never climb up without someone holding the ladder, because wet surfaces are slippery.
Pooled water should not be swept away with a hard brush, which can tear the surface. If the water is deep, the deck may be failing and the structure needs checking before anyone puts weight on it. Please call us instead of going up yourself. Heavy items placed on a weak deck, such as sandbags or paving slabs, can make matters worse.
From temporary patch to proper repair
Once the roof is dry and safe to work on, we find the cause. That might mean repairing a split, resealing a seam, replacing an outlet, forming a new upstand or recovering the whole roof. For typical national figures, MyBuilder's flat roof guide, updated in August 2026, gives replacement costs per square metre by material, and Checkatrade's roof repair guide gives repair figures. Neither is a price for your own roof; they only show the scale of typical work.
After surveying, we send a priced quote on paper, illustrated with your own roof. We aim to do only what the fault needs, and a flat roof with one local failure may need a repair, not a new covering. Our work is guaranteed for ten years, with the guarantee set down on paper. Afterwards the roof and garden are left tidy and the debris leaves with us.
If a storm or a lightning strike caused the leak, tell your insurer promptly and keep receipts for temporary work. Our page on lightning damage to a roof explains what to look for. If the insurer has refused, see what to do when a claim is rejected. For the wider service, see our emergency roof repairs page. We cannot promise any claim will succeed.