Flat roofing in Holton Heath

Garages, canopies and the room across the back. Around Holton Heath the flat roofs are attached rather than main roofs: an integral or detached garage, a canopy over a front door, a utility or dining room built across the back, and the odd flat topped dormer. Most are torch on felt or a built up three layer system finished with a mineral cap sheet, with some GRP fibreglass on the newer ones. We lift a corner and look at the deck, because everything else follows from it. Plywood and OSB that has stayed dry can be re-covered. Chipboard decking that has been wet loses its strength and sags between the joists, so it comes off and new boards go on before any membrane.

Getting the water off. Ponding is the fault behind most of the leaks we are shown. Water that stays put pushes into every lap and seam and a frost then splits them. The usual causes are a fall that was never built in, firrings cut too shallow, tapered insulation crushed by foot traffic, or a rainwater outlet choked with grit and moss. We rebuild the falls so the roof drains at an outlet instead of in the middle, which is what BS 6229:2025 on flat roofs expects, then run water through and watch the gutter, hopper and downpipe take it.

Trims, upstands and seams. Very little goes wrong in the middle of a covering. The trouble is at the edge trim, the drip, the apron flashing where the roof meets the house, the kerb round an opening, and the laps. Felt gives you a blister, a bubble or a split. Single ply lifts at a failed seam. Fibreglass cracks where a sharp internal angle has been flexing. Everything soft comes out. The upstand is rebuilt to a height that will genuinely hold water back, and the seams are welded or bonded rather than taped over and hoped about.

Openings, abutments and the build up. A rooflight, a lantern, a Velux, an access hatch or a soil and vent pipe gets a kerb and a collar rather than a ring of mastic. Where the flat butts brickwork a lead cover flashing is chased into the wall, and on a parapet the coping and the tray behind it are checked. Older roofs of this kind are cold roofs, insulation between the joists and a still void above, and that void is where condensation gathers and interstitial damp rots the deck without anything showing on top. A warm roof cures it. Insulation goes down on top of the deck, the vapour control layer goes beneath the insulation, and no ventilated void is left to go stale.

No rate per square metre, because the square metres are the easy part and what is under the covering is what decides the job.

Getting to it. A detached garage at the end of a drive, a rear extension on a nineteen eighties house, and a flat topped dormer above a bedroom are three different jobs before anything comes off. A garage or a single storey extension will often come off a tower, anything above a two storey wall wants a scaffold, and the platform has to stand while the deck is open rather than for an afternoon. The work at height rules are why it is a priced line rather than something folded into a rate.

The deck under the covering. A sound deck can be re-covered. Chipboard that has been wet for years, or ply that gives underfoot, has to come off and be replaced, and you cannot tell which you have from the ground or from a photograph. We lift a corner before quoting, because the deck is the single biggest swing in the price.

The falls, and where the water is meant to go. Most flat roofs that fail were never laid to a fall, or the fall runs at an outlet that has since been blocked or built over. Correcting it with firrings is more work than laying a membrane and it is the difference between a roof that lasts and one that ponds. Upstands, edge trims and each outlet are priced one at a time, because that is where the hours and the leaks both are.

Comparing quotes? Ask which system is being quoted and how many layers, whether the deck is being renewed or covered over, whether the falls are being corrected with firrings, how the upstands, outlets and edge trims are detailed, and whether the scaffold and the skip are in the price. Two quotes for the same job are usually two different jobs.

A lot of the housing around Holton Heath went up in the nineteen eighties, and that tells you something useful about the flat roofs. They were built as cold roofs, with a thin layer of insulation between the joists, a chipboard deck and a three layer felt covering on a shallow fall. Those materials had a good run and they are all reaching the same point at roughly the same time, which is why one road often has several garage and extension roofs failing within a year or two of each other.

What that means for you is that a straight like for like re-cover is usually the wrong answer. If the deck is going anyway, the sensible move is to rebuild it as a warm roof, with the insulation above the deck instead of between the joists and the falls corrected while the boards are off. It costs a little more in insulation and firrings than putting felt back on tired chipboard, and it deals with the condensation problem that comes with a cold roof rather than passing it on to the next owner.

We cover Holton Heath, Sandford, Organford, Lytchett Minster and the villages towards Wareham, along with the rest of BH16, and the site visit is free. You are dealing with Bournemouth Roofing & Building, the trading name of Bournemouth Roofing & Building Ltd, registered in England and Wales, company number 15471719, which you can look up in a minute. Thomas Hannen's business, and he is the one who comes out to price the job, not a salesman. A verified customer's 10 out of 10 on Checkatrade. The visit and the written quote are both free.