The undercloak is a strip of fiber cement, slate, or plain tile fixed along the sloping edge of a gable roof, projecting slightly over the fascia or brickwork. It provides a stable, flat base for the mortar bed that holds the edge tiles in place. This prevents the mortar from sagging and gives the roof verge a clean, finished appearance while shedding water away from the wall.
Bed the verge tiles on a solid undercloak so the mortar doesn't crack and fall out over time.
Related terms
Drip edge
A metal flashing installed at roof perimeters to direct water away from the fascia and underlying wood.
Ridge tile
A specially shaped tile designed to cap the apex of a pitched roof.
Roof assembly
The complete system of interacting components that form a building's roof, from the structural deck up to the weatherproofing layer.