Flat roofing in Cranborne

Garages, garden rooms and the roof over an old bay. Village work is mostly small flat roofs attached to something older: a garage put up in the seventies, a garden room across the back, a porch, a boot room, and the little lead or felt roof capping a bay window. The coverings we meet are torch on felt, built up felt in three layers under a mineral cap sheet, tired GRP fibreglass, and now and then a genuine lead flat that has split along a bay. We strip a section and look at the deck first. Dry plywood or OSB can be re-covered as it stands. Chipboard decking that has drawn water is done for and new boards go down on the joists before anything else. Then it is EPDM rubber, fibreglass or a new torch on system, and single ply on anything with a long clear run.

Standing water and where it should be going. Ponding is the most common thing we are shown. Water that stays on a roof works into every lap and seam, and one hard frost opens them up. Usually the fall was never laid, the firrings have been cut too shallow, or the rainwater outlet has silted up under leaves from the trees around the village. We reset the falls with firrings or tapered insulation so the roof drains at an outlet rather than in the middle, which is what BS 6229:2025 on flat roofs asks for, and we check the gutter, hopper and downpipe take it away cleanly.

The details that fail. The middle of a covering rarely gives trouble. The edge trim, the drip, the apron against a wall, the kerb around a rooflight and the laps are where water gets in. Felt goes as a blister, a bubble or a split. Single ply lifts at a failed seam. Fibreglass cracks at a hard internal angle. Failed material comes out first. The upstand is carried up behind the covering rather than stopped at deck level, and each lap is welded or bonded, so nothing is left relying on a repair over a repair.

Openings, abutments and the build up. Every rooflight, lantern, Velux, hatch and soil and vent pipe needs a kerb and a collar, not sealant. Where the roof meets brick or flint we chase in a cover flashing in lead, cut so it can move without splitting. On a parapet we look at the coping and whether a cavity tray sits behind it. Most of the older flat roofs here are cold roofs, insulation between the joists with a still void above, and that void is where condensation and interstitial damp rot the deck out of sight. A warm roof turns that around. The insulation is laid over the boards on a vapour control layer, the void goes altogether, and the joists spend the winter dry.

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 garage on a gravel drive, a garden room built off an old brick wall, and a bay top under an upstairs window are three different jobs before anything is stripped. 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.

Cranborne has its own conservation area, and there are a good many listed entries in and around the village, Cranborne Manor House among them. For flat roofing that has two practical consequences. The first is appearance. Putting like back for like is maintenance and needs nothing. Changing what a roof looks like where it can be seen from the street or the green, adding a lantern or a run of rooflights, or fitting a bright trim in place of a dark one is a planning conversation, and it is far cheaper to have it before the order goes in.

The second is consent. If the building is listed, or your flat roof is on something attached to a listed building, you need listed building consent even for a like for like repair, and that is separate from planning permission. Where an old lead flat is being replaced on a listed building, expect to be asked to put lead back rather than a modern membrane. For an ordinary house in the village none of this bites, and the only real decision is which covering suits the roof.

We cover Cranborne, Boveridge, Alderholt and the villages along the chase, and the rest of BH21, and the site visit and written quote are both 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.