Proper flashing is a critical component of all roof systems. On steep-slope shingle applications, flashings at vertical intersections are completed with metal step flashings. Step flashings should be fabricated from a non-corrosive metal such as minimum 24-gauge galvanized metal or 16-ounce copper.
The step flashing is applied over underlayment that is applied over the vertical substrate and under the shingle. The step flashing should extend a minimum of 4 inches up the vertical surface, and a minimum of four inches onto the substrate (under the shingle). The step flashing is fastened to only the deck — with appropriate fasteners — with one fastener per flashing. Fastening of step flashing is not recommended at vertical surface to allow for movement. The fasteners should be placed on the high (up-slope) portion of the horizontal metal piece so that fasteners are covered over by the overlapping step flashing. Step flashing should overlap a minimum of 2 inches, and application should begin at the eave and rise up to the ridge.