Step Flashing Installation

Step flashing waterproofs the joint where a sloping roof runs alongside a vertical wall, such as a dormer cheek, the side of a chimney or a two-storey wall. Instead of one long piece, it uses many short L-shaped pieces, one per course of shingles or tiles, each overlapping the one below like the roofing itself. This allows the roof and wall to move independently without opening a gap.

Typical dimensions

Canadian guidance specifies pieces:

• rectangular and 75 mm (3 in) longer than the shingle exposure;
• bent to extend at least 100 mm (4 in) onto the roof and 100 mm (4 in) up the wall; and
• lapped over the next piece by at least 75 mm (3 in).

At walls other than masonry, the vertical leg runs 100 mm (4 in) up the wall behind the cladding and its sheathing paper.

Installation steps

1. Install the underlayment and turn it up the wall a short distance.
2. Lay each course of shingles up to the wall.
3. Place a step flashing piece on top of that course, just above the exposed edge, so the next course covers it.
4. Fasten the piece with a single nail high in the roof leg, never into the wall leg, so the wall and roof can move separately.
5. Lay the next course over the flashing and repeat.
6. Lap the wall cladding (or counterflashing on masonry) over the vertical legs.

Kick-out flashing

Where a roof edge ends against a wall that continues below it, a kick-out (diverter) flashing at the bottom of the run turns water into the gutter rather than letting it run down behind the wall cladding. Building America guidance stresses integrating roof-wall flashings with both the underlayment and the wall's water-resistive barrier.

Other coverings

On tiled and slated roofs in the UK and Europe, lead soakers (the equivalent of step flashings) are often combined with stepped lead cover flashings dressed into the mortar joints of masonry. Metal roofs normally use a continuous sidewall flashing instead.