Flat Roofing in Knaphill

In Knaphill the same roof keeps coming up: a seventies felt covering on a rear extension or garage, laid on chipboard with almost no fall, now holding water in a shallow pond after every wet spell and staining the ceiling below.

Scott has spent more than 36 years on Surrey roofs, still answers the phone himself, and covers flat and pitched roofing in Knaphill with the firm's own roofers rather than subcontractors.

Call 07428 300474 any time for a free survey and an honest fixed price in writing.

Flat Roofing Systems

A flat roof is not flat. It is a low pitch roof, and BS 6229 expects a finished fall of at least 1:80 after deflection, which in practice means designing to 1:60 so the fall survives timber settlement. Most of the failures we open up in Knaphill are not membrane failures at all, they are ponding caused by a deck laid dead level or a fall running towards a blocked outlet.

There are four systems we work in, and each one suits a different deck and a different use:

• EPDM rubber, a single sheet of 1.2mm or 1.5mm synthetic rubber, bonded and cut to size on site so a garage or extension roof can be covered in one piece with no field joints.
• GRP fibreglass, a 450g chopped strand mat laminated into polyester resin over an 18mm OSB3 or WBP ply deck, topflowed to a seamless finish, best where the roof gets walked on.
• Felt, torch-on and built-up, a two or three layer system of SBS modified bitumen, vented base sheet, underlay and mineral cap sheet, with fully welded laps.
• Warm roof upgrades, where the insulation sits above the deck rather than between the joists, so the deck stays warm and the dew point moves out of the structure.

The system is chosen for the deck and the detail, not for what is quickest to sell.

Flat Roof Replacement and Flat Roofing Materials in Knaphill

Knaphill has a lot of the same building stock: post war semis with a rear kitchen extension, single garages with a slight fall to the front, and dormers and porch canopies bolted onto pitched houses. The common thread is a felt roof laid in the seventies or eighties on 12mm chipboard, which swells the moment water gets past the cap sheet. Once the board is soft, recovering over the top only buys a season.

A replacement runs in a set order:

• Strip the old covering back to structure and bag it off the roof, not down the drive.
• Inspect joists, ends and wall plates, and cut in new timber where rot has taken hold.
• Lay a new deck, 18mm OSB3 or ply, screwed at 300mm centres, with firrings to correct the fall.
• Fit insulation, upstands, drips, trims and outlets before any waterproofing goes down.
• Install the membrane, dress the upstands 150mm above finished level, and terminate into a chase or under a lead flashing.

Material choice follows the detail. GRP wants a dry deck and a settled temperature, so it is a poor call in a wet week. EPDM goes down cold with no flame, which matters against a timber fascia or under a low window. Torch-on is a sound answer on a large deck with straightforward geometry. We will say which one your roof wants and why, in writing.

Flat Roof Waterproofing and Insulation

Waterproofing is decided at the edges. A membrane rarely fails in the middle of a field. It fails at the upstand, the outlet, the pipe penetration and the junction with the pitched roof above, which is why leadwork to Lead Sheet Association guidance sits alongside the flat work rather than after it.

Insulation is where a flat roof either dries out or slowly rots. A cold roof with insulation between the joists needs a continuous 50mm cross ventilated void and a sealed vapour control layer below, and BS 5250 is clear about how easily that gets compromised by a downlight or a loft hatch. A warm roof avoids the argument. PIR board, typically 100mm to 150mm depending on the target U value, is bonded above the deck with a vapour control layer beneath it, the membrane goes over the top, and there is no cold cavity left to condense in. Where a re-roof renews more than half of the roof area, Approved Document L brings the thermal upgrade into scope, so we price that in from the start rather than raising it halfway through.

Rainwater sizing follows BS EN 12056, which means the outlet and gutter are sized to the roof area rather than matched to whatever was there before. Whether you need flat roofing in Knaphill or flat roofing in Godalming, the same detailing applies across the area we cover.

Commercial and Domestic Flat Roofing

Domestic work is extensions, garages, dormers, porches, bay tops and balconies. Commercial work is larger single decks, plant penetrations, parapet gutters and roofs that have to stay watertight while the building below carries on working. The engineering is the same, the staging is different.

The staging is the part most people actually worry about, and it is worth being plain about it. On a domestic flat roof you keep the use of your house. Scaffold or an edge protection system goes up first, the strip and re-deck happen from outside, and the room below stays a room: nothing comes through the ceiling and no internal work is needed unless the joists have gone. Torch-on work is noisy for the hours the laps are being welded, EPDM is close to silent. Rooms directly under the deck get dusty at strip stage, so we sheet up what is below where access allows. The deck is never left open overnight without a temporary waterproof covering, so a change in the weather does not become a leak indoors. Skips and materials are placed by agreement, not dropped wherever the lorry stops. Every day ends with the site swept and offcuts and fixings cleared, because standing on a nail on your own drive is nobody's idea of a finished job.

Flat Roof Repairs and Flat Roof Installation

Not every roof needs replacing, and we say so when it does not. A split lap, a failed outlet collar, a perished GRP trim joint or a slipped flashing is a repair, and a repair that is properly welded or bonded into sound existing material will last. What cannot be repaired is a saturated deck. Once water is held in the boards, patching seals the water in.

Diagnosis runs in this order: read the internal staining and where it appears in relation to the fall, walk the deck for soft spots, lift a lap or take a core where it is genuinely unclear, then check outlets and upstands for standing water marks. A drone view helps on roofs where getting a ladder to a safe angle would take longer than the inspection.

Installation, whether it is a new garage roof or part of a wider set of flat roofing services, is done to BS 6229 for the flat work and BS 5534 for fixing and wind uplift on any adjoining tile or slate that has to be lifted and reset. Our own roofers do the work, and the 25 year written workmanship guarantee is handed over before the team leaves. If something is not right inside those 25 years, we come back.