Where flat roofs usually let water in
Because a flat roof has no overlapping tiles, any break in the covering lets water straight through. The weak points are predictable:
- Joints and laps between sheets of felt
- Upstands, where the covering turns up against a wall
- Drip edges and trims along the front and sides
- Outlets and gutters, especially if they are blocked
- Low spots where puddles sit and slowly work into the surface
- Around roof lights, vent pipes and anything else poking through
Felt that has failed
Old felt roofs dry out in the sun and go brittle. You may see splits along the seams, bubbles where moisture has got trapped underneath, or a pattern of fine cracks across the surface. Each of these lets water reach the deck. Once the boards beneath are wet, they swell and soften, and the leak inside gets worse even if the outside looks much the same.
If several of these signs are showing, our guide to how long a flat roof lasts will help you judge how far gone it is.
Leaks where the roof meets the wall
On rear extensions, the junction with the house wall is a very common problem. The covering should turn up the wall, with a lead flashing or trim tucked into the brickwork above to stop water running behind it. If that lead has slipped, the mortar has fallen out, or the upstand was never high enough, water runs down the face of the wall and into the room below. Renewing the flashing and the upstand often cures it without touching the rest of the roof.
What you can safely do in the meantime
Keep everything indoors and on the ground. Place a container under the drip and move anything that could be damaged. In a garage, lift stored boxes off the floor and away from the wet area. If water is near light fittings or sockets, keep clear and switch that circuit off if you are unsure. Please do not walk on a leaking flat roof: a wet deck can give way underfoot.
Repair or full replacement
If the leak is from one split, a lifted edge or a tired flashing, and the rest of the roof is firm, a repair makes sense. If the felt is cracked all over, there are soft areas, or it has already been patched more than once, a new roof in GRP fibreglass or EPDM rubber is normally the better long-term answer.
Our flat roofing page explains how we strip and relay a roof. To understand what drives the price, see the flat roof replacement cost guide, and for help choosing a covering, read GRP vs EPDM.
Booking a visit
Lee Draper will check the roof surface, the edges and the wall junction, and look at the ceiling or garage underneath to see how far the water has gone. You then get a written quote for either the repair or a replacement, with his honest view on which is worth doing. Active leaks are prioritised within our working hours.
Call 07947 758052, Monday to Friday, 8am to 5pm, or request a visit online. Pitched roof leaking instead? See what to do when your roof is leaking.
Why a quick patch often fails
It is tempting to paint a tin of bitumen or sealant over a crack on a flat roof and hope for the best. Sometimes that holds for a while. More often, water has already got under the covering and spread across the deck, so the leak simply reappears somewhere else a few weeks later. Sealant also sticks poorly to dirty or damp surfaces and can trap moisture underneath.
A lasting repair means cleaning back to sound material, making sure the deck below is dry and firm, and using a patch that is compatible with the existing covering. On felt that is worn out all over, no patch will last long, which is why Lee will be straight with you if replacement is the better spend. You will get both options in writing so you can decide.