Flashing is what seals the joints in a roof: where it butts against a wall or a chimney, around every pipe and skylight, down the valleys and along the edges. Pennsylvania’s residential code calls for flashing at all of them. Repairing it starts with finding which joint the water is getting through, because each one is flashed, and fixed, in its own way.
Several of those joints have a post to themselves. A chimney is sealed in layers, and why a roof leaks around the chimney goes through each of them. There are posts, too, on the boot that seals a plumbing vent pipe, the lining under a roof valley, and the flashing and seals around a skylight. The rest are here, starting with the walls.
Flashing along a wall
Where the slope of a roof runs alongside a wall, as it does at the sides of a dormer, the joint is meant to have step flashing. That’s a run of L-shaped pieces of metal laid in course by course with the shingles, each piece lapping over the one below it. One leg lies on the roof under the shingle. The other stands up against the wall, and the siding goes over that leg, not under it.
Done right, the siding stops a little above the roof, so a strip of the step flashing shows between the bottom of the siding and the shingles. Rain coming down the wall drops onto that metal and is carried down the roof to the gutter.
Where the eave, the lower edge of the roof, runs into the wall, the code also wants a flashing that turns the water away from the wall. That piece is a kickout, and it sends the water into the gutter. Without one, the water coming down that stretch of roof can spill down the face of the wall, streaking it, and in time rot the trim below and get into the wall itself.
Watch for two installation mistakes along a wall. One is step flashing laid on top of the siding instead of tucked under it, which lets the wall behind take on water. The other is flashing nailed through the siding, which leaves holes for water to get into the wall.
The edges need it too
Pennsylvania’s code requires a drip edge on a shingle roof, along the eaves and up the rakes, the sloped sides of each gable. It’s metal at the very edge of the roof that helps keep water from running back behind the fascia. Where there’s a gutter, the drip edge should reach down into it.
What failing flashing looks like from the yard
You can make a first check standing in the yard, or from an upstairs window that looks out over a lower roof. Along each joint, look for:
- Rusty metal, or rust stains running down from it onto the shingles or the wall.
- A piece that’s bent, lifted or pulled away from the wall, the chimney or the pipe it should hug.
- Siding that sits right down on the shingles, with no metal showing beneath it.
- A dark streak or stain down the wall below the bottom corner of a roof.
- Tar or caulk smeared along a joint, the sign of an earlier patch.
Mixed metals are one cause of corrosion. When two different metals touch in a wet spot, one can eat away at the other, so copper flashing nailed down with aluminum nails will corrode.
If the first sign was a stain inside, how to detect hidden roof leaks shows how to follow it up into the attic and narrow down which joint let it in.
Replacing it, and what else may need fixing
Where step flashing along a wall has failed, new pieces have to be worked in with the shingles, so the shingles beside the wall come up first. Because that metal belongs under the siding, the bottom of the siding may have to come off as well, and a missing kickout should go in with the new flashing.
The repair can also reach the wood. Decking under a joint that has leaked a long time may be soft, and on a wall, the sheathing behind the siding can rot fast where a kickout is missing.
What a flashing repair costs depends on how much has to come apart to reach it. Our post on roof repair costs in Allentown puts damaged chimney flashing among the moderate repairs.
Our written price for repairing flashing that’s visibly failing costs you nothing. Call (484) 553-0213 and we’ll come out to see it.