Chesham Flat Roof Replacement

This flat roof replacement was carried out on a residential property in Chesham, Buckinghamshire, within the HP5 postcode area. The existing flat roof covering had deteriorated beyond repair, with blistering and cracking across the surface that meant patch repairs were no longer a viable option. The homeowner needed a complete strip and replacement to restore reliable weatherproofing and protect the structure beneath.

Chesham sits at the end of the Metropolitan Line in the Chiltern Hills, and properties in the HP5 area are exposed to driving rain and cold winters that test any flat roof. A proper replacement here means stripping back to a sound deck, checking the structure underneath, and building up a new layered system that is designed to shed water and stand up to UV exposure for years. You can read more about our flat roofing services and see our other completed roofing projects for reference.

The homeowner had previously experienced recurring leaks that required repeated roof repairs, and the decision was made to invest in a full replacement rather than continue patching a failing surface. Our recommendation was a 3-layer torch-on felt system, a proven, durable flat roof build-up that provides excellent waterproofing when correctly installed on a sound deck.

Work began by stripping the existing flat roof covering completely. The old felt and any damaged decking were removed to expose the timber structure beneath, allowing us to inspect the joists and confirm they were sound and capable of receiving the new roof build-up. Stripping back to a bare frame is essential on a flat roof replacement: laying new felt over a failing deck simply hides the problem and shortens the life of the new system.

With the structure checked, we installed new 18mm OSB3 ply boards across the roof. OSB3 is engineered for humid conditions and provides a solid, dimensionally stable deck that will not delaminate or warp beneath a torch-on felt system. Each board was securely fixed and the joints staggered to create a continuous, firm surface with no movement that could stress the felt layers above.

Over the new decking we built up the 3-layer torch-on felt system. The first layer was a perforated underlay, torched directly onto the OSB3 deck, which acts as a vapour control layer while allowing the boards to breathe. Over this we applied a layer of bitumen underlay, torched and bonded to the layer beneath to build the waterproof thickness of the roof. The final layer was a mineral cap sheet, torched on top to provide the weatherproof surface finish. The mineral surfacing gives the roof its UV protection and a durable, hard-wearing top layer that resists foot traffic and weathering.

Each layer was fully bonded to the one beneath, with all laps sealed and rolled tight to prevent any water ingress at the joints. The edges and details were dressed carefully to ensure water sheds cleanly off the roof and into the guttering, with no ponding areas left behind. The result is a continuous, seamless waterproof membrane that covers the entire flat roof from edge to edge.