What this piece is for
Where the covering stops against a chimney, a wall, a pipe or a skylight, water would find a way through. The flashing catches it and sends it back over the top of the covering. The condition of the flashing counts for a lot when deciding to repair or replace a roof: a covering still in good shape can leak through its flashing, and a new roof can leak through old flashing.
What wears out a flashing
A continuous surface of shingles or membrane gives water little to grab onto. A joint between two materials gives it several.
- Each material moves in its own way. Brick, wood and metal do not swell or shrink at the same rate, and the joint is strained from one season to the next.
- Sealant has a short life. The sealant that closes the top of a counter-flashing hardens, cracks and often comes loose well before the end of the roof's life.
- The rubber sleeve bakes in the sun. Around a vent pipe, the sleeve eventually splits.
- The brick joint empties. When the mortar goes, the counter-flashing set into it no longer holds.
- The original installation was poor. Too short, badly nailed or smothered in sealant to make up for it, a flashing holds a few years before failing.
- The old flashing was left in place during the replacement. The job goes faster, but the new covering inherits the weakness of the old one.
Where flashing is found
The chimney. Along its sides, L-shaped pieces are stacked in steps, each one inserted between two courses of shingles. Above them, a counter-flashing set into the masonry joints covers the top of these pieces.
Where a roof meets a taller wall. The flashing runs up behind the wall cladding and covers the edge of the roof covering.
Vent pipes. A boot fits around each plumbing pipe. Its flat base slides under the covering, and its sleeve, rubber or metal, hugs the pipe.
The perimeter of a flat roof. The membrane runs up against the walls and parapets: this is the upturn. A counter-flashing shelters its top, and a metal cap covers the top of the low wall.
From sealant to the redone detail
Redo the sealant. This is a maintenance step, quick and inexpensive, that will need repeating.
Change a piece. A vent boot or a section of flashing can be replaced without redoing the roof, but not without opening it. We take apart the covering around it, slide the new piece underneath and close it again.
Redo the whole detail. At a chimney, we redo the step flashing and the counter-flashing, this time properly set into the masonry.
This work is done at height and is the roofer's job. Just note where the stain is and in what weather it appears.
Frequently asked questions
What clues point to a flashing rather than the roof covering?
A stain near a chimney, an exterior wall or a vent pipe points toward the flashing. So does a leak that only shows up when rain is driven by wind. Only a roofer, on the roof, can confirm it.
Do you need new flashing when the roof is redone?
Yes, it is strongly recommended. Old flashing is unlikely to last as long as the new covering installed against it. Have its replacement written into the quote.
Can you get by with adding sealant every year?
On sound flashing, sealant buys time. It does not repair metal with holes in it, a piece that is too short or a poor installation. A joint that keeps needing more is hiding another defect.