What is torch-down roofing?

Torch-down roofing, also called torch-applied modified bitumen, is a roofing system where rolls of bitumen-based material are heat-sealed to a roof substrate using a propane torch. The contractor unrolls the membrane across the deck surface, applies direct flame to the underside or top surface of the roll, and bonds it permanently to the base layer through controlled heating. This creates a monolithic, watertight seal without adhesives or fasteners.

The torch-down method works on both new construction and re-roofing applications. Common substrates include plywood, concrete decks, or existing tar and gravel surfaces. The material typically comes in rolls 3 to 4 feet wide, laid in overlapping runs that are sealed at the seams as installation progresses. Once cooled, the fused bitumen hardens into a durable membrane.

Torch-down systems are standard on flat commercial roofs, low-slope warehouse and light industrial buildings, and flat garage or outbuilding roofs across Ontario. The approach offers good durability in cold climates and handles freeze-thaw cycles well. Because the seal is created through heat fusion rather than glue or nails, it resists wind uplift and accommodates substrate movement.

Roofers specializing in flat roofing typically carry modified bitumen stock and maintain torch-down crews. The system requires proper ventilation during application and careful torch handling to prevent over-heating or damage to the membrane.