Step flashing is the L-shaped piece that goes course by course along a roof-to-wall intersection - chimney sides, dormer cheeks, sidewalls behind shingles - to keep water from running back into the wall. Each piece overlaps the next as the shingle courses climb, weaving into the roof so any water that drives behind the siding gets directed back out onto the next shingle below.

• Application: Roof-to-wall intersections, dormer cheeks, chimney sides, skylight curbs, and any vertical surface where shingles butt a wall
• Material: 29 gauge G90 hot-dipped galvanized steel
• Finish: Hot-dipped galvanized zinc coating - more abrasion resistant than aluminum and the right pairing when the existing flashings on the structure are also steel
• Piece size: 5" x 7" (flat dimensions before bending)
• Bending: Bend on site to match the roof pitch using a metal brake, a vise plus a hardwood block, or a pair of seamers - aim for a slight overbend so the leg lies flat against the wall sheathing
• Workability: Cuts with tin snips, trims to length with a chop saw or shears, takes a hammer-formed reveal at the top of the wall leg
• Compatibility: Works with most three-tab and architectural asphalt shingles plus slate and tile profiles when sized to the course exposure
• Quantity: Sold each

Tip: Install one piece per shingle course with the vertical leg behind the siding or counterflashing and the horizontal leg overlapping the shingle below by roughly the course exposure. Fasten near the top of the wall leg into wall sheathing only - never face-nail through the horizontal leg where standing water would sit on the shingle. Pick galvanized steel when matching existing steel flashings on the structure or when the side of the wall sees abrasive contact (vines, ladders, equipment) that would scuff thin aluminum.