Types of Roof Flashing: A Contractor's Guide
Every roof runs more than one kind of flashing, and each one covers a specific weak spot where water wants to get in. Know which piece goes where and you spec it right the first time. Get it wrong and you are back on the roof chasing a leak that never should have happened.
Step Flashing
Step flashing handles the spot where a sloped roof runs into a vertical wall, a dormer, a chimney, or the side of an addition. Instead of one long piece, it is a stack of small L-shaped pieces, each one stepped up the slope. The roofer sets a piece on top of each course of shingles before the next course goes down, so the flashing weaves right into the roof.
That layering is the whole reason step flashing holds up. There is no long continuous seam to split open down the road, just piece over piece, each one shedding water onto the one below. For steep-slope work we brake-form it in 5" × 7" pieces at minimum, but we cut the profile to whatever your detail calls for. Galvanized steel, aluminum, or copper.
Counter Flashing
Counter flashing caps the top of the step flashing where it meets the wall. The step flashing runs up alongside the roofing, and the counter flashing tucks into the wall above it and laps back down over the top, so water cannot sneak in behind.
Here is the part people miss. Counter flashing is supposed to leave a gap between the roof system and the wall system. The two move at different rates when things heat up and cool down, and that gap lets them. Lock them together and that movement pops fasteners and cracks your sealant in a season or two. On masonry, the counter flashing sets into reglets cut into the mortar joints and seals in there.
Kickout Flashing
Kickout flashing, some folks call it diverter flashing, sits at the very bottom of a step flashing run, where the wall keeps going down past the roof edge. Its one job is to throw the water that has been tracking down that roof-to-wall seam out into the gutter, instead of letting it dump in behind the siding.
Leave it off and you have a problem. Missing kickout is one of the top reasons water gets behind cladding, and it is brutal on fiber cement and stucco. The water hides behind the wall, rots the framing, grows mold, and runs up a repair bill that dwarfs what the flashing would have cost. This is one to fabricate custom, not pull off a shelf. We form it to the exact geometry of your roof edge, gutter, and fascia.
Base Flashing
Base flashing works the bottom of the vertical stuff on a roof, where a flat surface like a roof deck butts into a parapet, a chimney, a curb, or a mechanical unit. It carries the waterproofing up and over that horizontal-to-vertical turn so the seal never breaks.
On a flat roof, base flashing runs up the face of the parapet at least 8" above the finished roof, with the bottom worked into the roofing membrane. Up top, coping or counter flashing laps over it to finish the assembly. Pick your material with care here. It has to play nice with the membrane, take the heat that builds up at roof level, and outlast the roof it is protecting.
Frequently Asked Questions
What is the most common type of roof flashing?
Step flashing is the most commonly specified type at roof-to-wall intersections. Counter flashing is typically installed over step flashing to complete the assembly and seal the top of the flashing against the wall surface.
What gauge should roof flashing be?
Typically 24-gauge galvanized steel (G-90), 0.040" aluminum, or 16–20 oz copper, depending on application and compatibility with adjacent materials. The right choice depends on the roofing system, climate, and project spec.
Can PDX Panels custom-fabricate any of these flashing types?
Yes. We brake-form step flashing, counter flashing, kickout flashing, base flashing, and any other profile you specify. Custom profiles from drawings, field measurements, or sample pieces. Call (503) 914-0210 or submit a quote request online.
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