A torch-on underlay is the essential base layer of a multi-layer flat roofing system. It is specifically designed to be applied using a gas torch, which melts the bitumen on the underside to create a permanent, waterproof bond with the roof deck or the layer below. Underlays provide the primary waterproofing integrity before the final mineral capsheet is applied.
Why use a torch-on underlay?
Unlike traditional pour-and-roll methods, torch-on underlays offer a faster and more reliable installation. They are typically reinforced with polyester or glass-fibre to provide strength and flexibility, ensuring the roof can withstand thermal movement and foot traffic.