Step Flashing

Step flashing is the method used to seal the joint where a sloping roof runs alongside a vertical wall, such as a dormer cheek, a second-storey wall or the side of a chimney. Instead of one long strip, it uses many short L-shaped (bent) pieces of metal. Each piece is laid over a course of shingles, with one leg on the roof and the other turned up the wall, and the next course of shingles covers its roof leg. The result steps up the slope, overlapping like the shingles themselves, so water is always shed onto the course below.

In the UK and Ireland, the equivalent concealed pieces under tiles and slates are called soakers, and the visible metal stepped into the brickwork above them is a stepped cover flashing.

Typical dimensions and installation (North America)

US Department of Energy guidance summarising the IRC calls for each piece to extend at least 4 in (102 mm) up the wall and 4 in (102 mm) onto the roof deck, with retrofit guidance suggesting 5 in (127 mm). Pieces must overlap shingle-fashion, each upper piece over the one below; underlapped pieces can channel water into the wall. Corrosion-resistant metal of at least 0.019 in (0.48 mm), about 26-gauge galvanised steel, is the usual minimum.

Key details:

• Underlayment is laid first and turned up the wall.
• The wall's water-resistive barrier or house wrap laps over the top of the step flashing, not behind it.
• Siding or cladding is held about 1 in (25 mm) above the roof surface.
• The lowest piece at the eaves becomes or is followed by a kickout flashing.

Covering the top edge

Step flashing is not sealed to the wall. Its upper edge is protected by the wall cladding or by a counter-flashing let into masonry. This allows the roof and wall to move independently.

Common faults

Using a single long piece instead of separate steps, nailing through the vertical leg low on the wall, missing kickouts, and caulk used in place of proper laps are frequent causes of sidewall leaks.