Flat roofing in Taunton

The fall is the slope built into a flat roof to move water off it. BS 6229:2025 keeps a minimum finished fall of 1:80 for general roof areas and internal gutters. That is the least the roof should end up with once the timbers have settled and the boards have deflected a little, which is why IKO's guidance is to design a roof for a fall of 1:40. A roof designed to the bare 1:80 can easily finish flatter than that, and then the water sits. Some older roofs were laid with very little fall at all, or have sagged between their joists, which shows as a row of shallow dishes. Our answer on the fall a flat roof needs works through the numbers.

Sometimes the answer is at the outlet. A gutter outlet or rainwater pipe choked with leaves, moss or a lost ball holds water back across the whole roof, and clearing it ends the problem in an afternoon. Where the deck has dipped in one place, a small hollow can be built up as part of a repair. A roof that falls the wrong way, though, needs its falls rebuilt. That is done with firrings, tapered timber strips fixed along the joists, or with tapered insulation boards that carry the slope within the insulation itself. Either way the old covering has to come off, so it belongs with a replacement rather than a repair.

Every flat roof needs a planned exit: a gutter along the low edge, an outlet through a parapet wall, or a hopper head feeding a downpipe. If yours drains onto a tiled or slate roof below, or into a gutter that already overflows, the fault can show up somewhere else entirely.

In a cold roof the insulation sits between or below the joists, under the deck, with a ventilated gap above it, so the deck itself stays at outside temperature. In a warm roof the insulation goes on top of the deck, under the waterproof layer, with a vapour control layer beneath it, so the deck and joists stay on the warm side. The cold roof is the older arrangement. It depends on air moving through small vents at the edges, and on small extensions and dormers that air path is easily blocked by insulation or a later ceiling. When we replace a flat roof deck, a warm roof build-up is usually what we recommend for that reason. Our guide to warm and cold flat roofs explains both build-ups in more detail.

Condensation. Warm, moist air from a kitchen or bathroom below rises through the ceiling, reaches the cold underside of the deck and turns to water. It can soak the insulation and drip from light fittings, and it is easy to mistake for a leak. The giveaway is dampness spread evenly, at its worst on cold, calm nights instead of in stormy weather. Designers work to BS 5250:2021, the moisture code, here.

Approved Document L lists replacing the waterproof membrane on a flat roof as renovation. Under Table 4.3 of the 2021 edition, a roof worse than 0.35 W/m²K is expected to be upgraded to 0.16 W/m²K, unless that is not technically or functionally feasible or would not pay back within 15 years, in which case it is upgraded as far as is feasible (para 4.13). Your building control body confirms what applies to your roof.

Going by the Planning Portal, you normally need no building control application when less than 25 per cent of the total building envelope and less than 50 per cent of the roof is affected. Replacing the membrane also counts as renovation under Part L, so check before work starts. Somerset Building Control charges re-roofing as renovation of a thermal element when it is notifiable, and it publishes no re-roofing threshold of its own; its number is 0300 303 7790. Our guide to flat roof replacement and Building Regulations covers the detail.

Planning is simpler. On a house, a new roof covering is normally permitted development under Class C, though those rules do not reach a building containing flats. Listed homes need listed building consent as well, and in a conservation area ask Somerset Council's planning team first if the look of the roof will change. Inside Exmoor National Park, Exmoor National Park Authority is the planning authority.

We agree a start date, set up safe access and protect the garden and paths below. The old covering comes off a section at a time, the deck is checked and renewed where needed, and nothing is left open overnight. The new system goes on, then the trims, upstands, flashings and outlets, and the gutter is checked last. Scaffold standing on the pavement needs a scaffold licence (Highways Act 1980 s169) from the highway authority, arranged with the scaffolder before the start date. Waste leaves as the work goes, and at the end of each day we tell you what the next one holds. Rain stops the laying, because membranes and resins need a dry deck, so winter work goes ahead on dry days with the roof sheeted over between them.

If your flat roof is leaking or ponding, take a photo from an upstairs window and send it with your booking, so the survey visit starts in the right place.