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Flat roof leaking

Flat roofs over extensions, garages and dormers leak more than any other kind, because water sits on them rather than running off. The good news is that a flat roof is also the easiest to inspect properly, so it is usually clear within a few minutes whether a repair will hold or the covering has had its day.

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Signs to look for

  • Water dripping or staining on the ceiling of an extension or dormer
  • Puddles that are still there a day or two after rain
  • Blisters, cracks or splits in the felt surface
  • Felt lifting at the edges or where the roof meets a wall
  • A spongy feel underfoot, which usually means wet decking below
  • Green growth or moss in the low spots

What causes it

Traditional felt roofs have a typical life of fifteen to twenty years, less in full sun. As the bitumen ages it dries, cracks and blisters, and the joins open. A roof at that stage can be patched, but it will keep finding new places to leak.

Ponding is the second big cause. If the deck has sagged or the falls were never right, water stands in the same place for days and works its way through any weakness. Upstands and flashings, where the roof meets a wall or a door threshold, are the third: they move more than the roof itself.

Blocked outlets and gutters let the roof fill like a tray. A drain choked with leaves can put water over an upstand that would never otherwise see it.

What we do

We inspect the covering, the edges, the upstands and the outlets, and where it is safe we check whether the deck below is still sound. If it is a defined failure on an otherwise healthy roof, we repair it. If the covering has reached the end of its life, we show you why and price a replacement.

For replacement we usually recommend EPDM rubber or a modern torch-on system, with the deck and falls corrected where needed, because putting a new covering over a deck that ponds simply repeats the problem.

What it usually costs

A local repair to a split or an upstand is a modest job. A full replacement depends on the size of the roof, the covering chosen and whether the deck needs replacing too, which we can only judge once we have looked. Every quote is free and fixed in writing, with the deck work shown as its own line.

Questions

Can you just put a coating on it?

Liquid coatings have their place on a sound roof. On a roof that is wet underneath they trap the water in, so we only recommend one when the deck is dry and the covering is otherwise sound.

How long will a new flat roof last?

A properly laid EPDM or quality torch-on roof should last many years longer than old felt, and both come with a written guarantee. The flat roof options guide compares them.

Is a wet deck a big problem?

It means the boards need replacing in that area before a new covering goes on. We show you the extent and price it as its own line, so nothing is hidden in the total.

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