Flat roofing in Corfe Castle

The traditional flat. A good many of the older roofs here are lead, laid in bays over a boarded deck with rolls and drips between them. Lead splits where it has been fixed too tightly to move, and it fatigues along a drip. Where the original is lead and the building is seen, lead is usually what should go back, and we will price it that way rather than talk you into a membrane.

The modern ones. Elsewhere it is felt: a three layer built up system with a mineral cap sheet, or a single torch on layer laid over the last covering. Those fail as splits along the creases, blisters where damp was sealed in, and a lifted seam at an upstand. On a plain rectangle we strip to the deck and lay EPDM rubber in one sheet, no lap and no seam in the field of the roof.

What is under it. Plywood, OSB or chipboard decking on joists, with firrings on top creating the fall. Chipboard that has been wet gives underfoot and comes off. A roof with no fall holds standing water, and that ponding is what kills a covering long before the weather does. Where we cannot re-firr we build the fall in tapered insulation. BS 6229 is the code the falls come from.

Insulation, and what it does to old timber. Over a heated room the insulation comes up with the covering under Part L. We take it above the deck: a vapour control layer first, PIR over that, membrane above, so the joists and the boards stay on the warm side of everything. The alternative is a cold roof, insulation packed between the joists, which leaves the deck below the dew point. Warm damp air from the room reaches it, interstitial condensation forms inside the construction, and in a thick walled old building the timber has nowhere to dry to. Building control are notified and inspect it open.

Junctions and openings. None of this is optional. A chase cut into the stone or brick, a lead cover flashing dressed into it, a cavity tray above where the wall is cavity built. A coping on the parapet with an apron under it. A kerb beneath every rooflight, lantern, Velux style flat roof window, hatch and soil or vent pipe, so the covering turns up an upstand instead of stopping at a frame. A drip trim along the free edges. And a rainwater outlet sized for the roof, running to a hopper, a downpipe or the gutter. A garage is a day, a back addition two or three working days, and we say how long first.

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 stone cottage with a lead flat over a back addition, a bungalow garage on a modern plot and a flat roofed extension behind a terrace are three different jobs before anyone unloads. 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.

The whole of the village core sits within the Corfe Castle Conservation Area, and there are well over a hundred listed entries in and around it. That combination is unusual even for Purbeck, and it changes the order you do things in. The rule of thumb is simple enough: like for like is maintenance, a change of appearance is not.

So a lead flat re-laid as a lead flat is repair. The same roof re-covered in a light grey membrane, where it can be seen from the street or from the castle mound, is a change the council will take a view on. Rooflights and lanterns are the other thing that gets noticed, because they add something that was not there before. And if the building itself is listed, the listing follows it all the way to the back, so even a hidden roof needs consent. None of this is a reason to leave water coming in. We make a leak safe first and sort the permanent covering once the paperwork is straight.

We cover Corfe Castle, Church Knowle, Kingston, Harmans Cross and the rest of BH20. 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.