Where flat roofs leak
Water on a flat roof moves slowly, so it finds every weakness. The trouble is usually at the details, not in the open field of the roof:
- Upstands and abutments, where the covering turns up a wall and the flashing above has cracked or pulled away.
- Edge trims and drip details, where wind lifts the covering or the trim has come loose.
- Outlets and gutters, choked with leaves, moss or silt, so water rises over the edge of the membrane.
- Joints and laps in felt or around rooflights, soil pipes and vents.
- Splits and cracks caused by the roof moving, or by people walking on it.
Leaks inside often show well away from the fault, because water runs along the deck and joists first. So we inspect the whole roof, and the ceiling below, before deciding what to repair.
We also check what is underneath. Pressing on the covering tells us whether the deck is firm, and on a cut-out repair we can see whether the board or joists are wet. Somerset's mild, damp winters mean a deck that has been wet for a while may already be soft, and patching over rotten timber never lasts.
Repairs by roof type
Felt (reinforced bitumen) roofs
Splits, open laps and small blisters can be cut out and patched with compatible membrane. A blister that is dry and stable may only need watching. One that is growing, or soft and wet underneath, usually means water or condensation is trapped below the felt. Where the cap sheet has worn but the layers beneath are sound, a new cap sheet can sometimes extend the life of the roof.
EPDM rubber roofs
Most EPDM problems are at the details: a lifted edge, a corner that wasn't sealed properly, or tape around an outlet that has failed. Holes and tears are cleaned, primed and patched with EPDM repair tape or membrane. Repair materials must be compatible with the rubber, so we repair like with like.
GRP fibreglass roofs
Cracks often follow joints in the board deck underneath, where it has moved or got wet. We grind back the damaged area, check the deck is dry and sound, and re-laminate with matching resin, matting and topcoat. If the board below has gone soft, that section of deck has to be replaced first, or the crack will just come back.
Patch, overlay or replace?
A repair is good value when the damage is local and the deck is dry and firm. It is poor value when we find several of these at once:
- soft, spongy or sagging deck across large areas;
- widespread blistering that is getting worse;
- water ponding in the same hollows, which a new covering won't fix;
- a roof that has already been patched many times.
When that happens we say so and quote for a properly built replacement instead; our new flat roof options page compares the materials. We'd rather tell you that up front than sell you a patch that fails next winter.
Condensation can look like a leak
Some flat roofs drip in cold weather even when they are watertight. Older roofs built with insulation between the joists and no proper ventilation or vapour control can collect condensation on the underside of the deck. If the drips come on frosty mornings rather than in rain, condensation is a likely cause, and the fix is about insulation and ventilation rather than patching the top. Our roof ventilation service explains more.
Looking after a flat roof
- Clear leaves and moss from outlets and gutters, particularly after autumn.
- Avoid walking on the roof unless it was designed for it.
- Don't let ladders, bikes or furniture lean against the edge trims.
- Have a look from an upstairs window after storms, and call us if you see lifted edges or debris.
If a balcony or roof terrace sits over a room, it needs extra care at the door threshold and drainage. Our balcony and roof terrace page covers that.
Getting your flat roof repaired
Our number is 07933 861 087 and our inbox is hello@somersetroofing.co.uk. Let us know roughly how old the roof is, what it's covered with if you know, and where the water shows. There's no call-out fee for the inspection; afterwards you receive pictures of the faults and a written price. Prefer a form? Book a flat roof inspection online.
Flat Roof Repairs: common questions
Can a flat roof be repaired in wet weather?
Some temporary repairs can be done in damp conditions, but most permanent repairs need a dry, clean surface. Felt patches won't bond to wet membrane, EPDM adhesives need a dry substrate, and GRP resin needs dry conditions and suitable temperatures to cure. If water is coming in, we make it weathertight first and come back for the proper repair when the weather allows.
My flat roof has blisters. Is it leaking?
Not necessarily. Small, firm blisters can be caused by trapped air or moisture vapour and may stay stable for years. Blisters that keep growing, spread across the roof, or feel soft and wet are more serious, because they suggest water or condensation trapped below the covering. We check whether the deck underneath is wet before recommending a repair or replacement.
Can you repair a GRP roof without replacing it all?
Usually, if the damage is limited. We grind back around the crack, make sure the deck is dry and sound, and lay new resin, glass matting and topcoat that bond to the existing laminate. The repair may show slightly where the colours meet. If the cracks follow deck joints across the whole roof, the boards are probably moving and a wider repair is needed.
Is it worth patching an old felt roof?
It depends on its overall condition. A single split or failed upstand on an otherwise sound roof is well worth repairing. If the felt is cracked all over, the deck is soft, or water ponds across large areas, patches only buy time. We'll give you a frank view with photos, and price both options if a replacement is worth considering.
Why does my flat roof drip on cold mornings?
That pattern often points to condensation rather than a leak. Warm, moist air from the room below rises into the roof, meets the cold deck and condenses, then drips back down. It is common in older cold roofs with poor ventilation or no vapour control layer. Patching the top won't solve it; the insulation and ventilation need to be looked at.
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