Step flashing should be 2 inches longer than the exposure of the roof shingles; in regions with severe weather, overlaps of 3 inches are common. For step flashing, use minimum 26-gauge galvanized steel, .019-inch aluminum, 16-ounce copper, or 20-pound terne metal.
Step flashing should be 2 inches longer than the exposure of the roof shingles; in regions with severe weather, overlaps of 3 inches are common. For step flashing, use minimum 26-gauge galvanized steel, .019-inch aluminum, 16-ounce copper, or 20-pound terne metal.
To prevent water from dumping behind the siding at the end of a roof-wall intersection, bend a small kick-out from metal flashing to divert water from the wall.
To prevent water from dumping behind the siding at the end of a roof-wall intersection, bend a small kick-out from metal flashing to divert water from the wall.

Step Flashing Checklist
  • Cut step flashing pieces 10 inches long and 2 inches wider than the shingle exposure. (For example, cut 10-by-7-inch step flashing for roof shingles with a 5-inch exposure.)
  • Bend the flashing in half lengthwise so that it extends 5 inches over the roof deck and 5 inches up the wall (see illustration, top right).
  • Place each step flashing piece about ¼ inch short of the bottom edge of the shingle that will overlap it — just enough so that the flashing piece is not visible when the overlapping shingle is in place.
  • Because the flashing is 2 inches wider than the exposure of the shingles, each step flashing piece will overlap the one on the course below by 2 inches.

  • Nail the flashing to the roof deck only. Do not nail it to the wall.
  • Bring wood siding down over the vertical sections of the step flashing to serve as counterflashing. Do not nail siding through the step flashing.
  • Kick-Out Flashing Because sidewall flashing must handle a large volume of water, one of the most critical flashing details occurs where the roof-wall junction terminates. To deflect water from the siding, install a kick-out in the corner (see illustration, bottom right).

    Though not always possible in the construction sequence, it's best to install a full 36-inch-wide piece of rubberized asphalt on the wall before nailing subfascia and trim boards in place, then come back to install the kick-out.

    This article is adapted from the JLC Field Guide to Residential Construction, Vol. 1, www.jlconline.com.