Step flashing protects the interface between a roof and a wall from water leaks that can cause hidden damage for years.

Step flashing can be made with aluminum, copper, lead, galvanized steel, or stainless steel, but most commonly it is aluminum or copper.

Small L-shape flashing pieces must be woven into the shingles as you work your way up the roof. The flashing integrates the roof cladding into the wall cladding to keep water out. Install the step flashing pieces so that they can easily be replaced during a  reroof job or else the damaged old flashing will be reused and the expensive new reroof will need to be redone (#Fail).

Here's how to do it right the first time:

1. Cut step flashing pieces to be 10 in. wide and 2 in. longer than the shingle’s exposure. This allows each step-flashing piece to overlap the piece below. Bend the 10 in. length to extend 5 in. up the wall and 5 in. over the roof deck.

2. Nail flashing to roof deck only. Nail through flashing into shingle, do not extend flashing above top of shingle and nail, or flashing will angle up. If nailed it to the wall, flashing will be impossible to replace when reroofing.

3. Cover tops of step flashing with house wrap and siding. Do not nail through tops of step flashing when installing siding.

Additional Information about flashing:

Kickout Flashing (Builder)
Flashing Primer (Journal of Light Construction)
Flashing the Tricky Spots (Journal of Light Construction)

This article is excerpted from the JLC Field Guide; we are working on updating the JLC Field Guide right here online, one detail at a time. If you see improvements that we can make on these details, please speak up in the comments section below.