Flat Roof Leaking? What Causes It and How It Is Fixed
If your flat roof is leaking, the water is almost always getting in at an edge, an upstand, a joint or a split, not through the middle of a sound covering. On felt roofs, standing water and cracked or blistered felt are the usual culprits; on garages and extensions it is often the trim or the junction with the house wall. Finding that true entry point is the whole job, because water travels across a flat deck before it shows on the ceiling below.
- Leak traced to its real entry point, not the stain
- Felt, GRP, EPDM and liquid roofs
- Garages, extensions, dormers and bays
- Ponding, blistering, splits and lifted edges
- Deck checked before repair or replace advice
- Photo report and written price
Why flat roofs leak
Edges and upstands. The perimeter takes the most movement and weather. Drip trims lift, felt pulls away from a wall, and the timber behind the trim softens. This is the most common source of a flat roof leak.
Ponding. A flat roof should still have a slight fall. Where the deck has sagged, water sits in puddles for days after rain, finds the smallest weakness, and speeds up wear on the covering.
Blistering and cracking. Trapped moisture or air under felt lifts blisters in warm weather. When a blister cracks, or old felt splits over a board joint, water goes straight in.
Junctions and outlets. Where the flat roof meets the house, a soil pipe, a rooflight or an outlet, the seal is only as good as the detail. Mastic and tape at those points fail long before the roof does.
Why does my flat roof only leak in heavy rain?
A leak that appears only in heavy or wind-driven rain usually points to an upstand, a flashing or a blocked outlet. Normal rain drains away; heavy rain backs up behind a blockage or is blown up under a lifted edge. That is useful information, so tell us when the leak shows when you call.
Why is my new flat roof leaking?
A newly laid roof that leaks almost always has a detailing fault rather than a failed membrane: an upstand that is too low, a trim fixed in the wrong place, or the old roof left in place underneath. Sometimes it is not a leak at all but condensation from a cold roof build-up, which drips in cold weather and looks just like one. Our guide to warm and cold roofs explains the difference.
How a flat roof leak is fixed
Once the entry point is found, a local fault on a sound roof can be repaired. Felt can be patch-welded, GRP can be ground back and re-laminated, and EPDM can be patched with the correct primer. See felt roof repair and fibreglass roof repair for how each works.
If the deck is wet and soft, or the covering is failing in several places, replacement is the honest answer, and a patch is money you will spend again. Our flat roof repair page covers both routes, and flat roof replacement cost explains the prices.
Can you fix it yourself? A tin of sealant over a crack may slow a drip for a few weeks, but it rarely bonds to old felt and hides the real condition of the roof.
Call 07840 996627, Monday to Friday 8am to 6pm. For active leaks we aim to attend the same or next working day, weather permitting, and make the roof safe first.
Flat Roof Leaking? What Causes It and How It Is Fixed FAQs
Why is my flat roof leaking?+
Most often through a lifted edge or upstand, a split or blister in the covering, or a junction with a wall, pipe or rooflight. Ponding water makes all of these worse.
Why is my garage roof leaking?+
Garage roofs are often older felt on chipboard or plywood with simple trims. Splits over board joints, lifted edges and rotted fascia boards are the usual causes.
Why is my new felt roof leaking?+
Usually a detailing fault at an edge, upstand or outlet, or condensation from a cold roof build-up rather than a hole in the new felt.
Is flat roof ponding a problem?+
A little water drying within a day or two is normal. Puddles that stay for days speed up wear and suggest the deck has sagged, which is worth checking.
Do you do emergency flat roof leak repairs?+
Yes. Ring 07840 996627 Monday to Friday 8am to 6pm. For active leaks we aim to attend the same or next working day, weather permitting, and make the roof safe before the permanent repair.
Need Roofing Work You Can Rely On?
Contact Stoker Property Solutions for new roofs, flat roofing, repairs and maintenance across Newcastle, Sunderland and the wider North East.