Where flashing is found
The condition of the flashing weighs heavily when it is time to repair or replace a roof. Here is where it sits.
Around the chimney. Pieces bent at a right angle step up along the sides, slipped between the rows of shingles. A counter-flashing set into the brick joints covers them from above.
At the base of a wall. When a roof meets a taller wall, the flashing runs up behind the siding and down onto the roofing.
Around vents. Every plumbing pipe that comes out of the roof wears a boot. It has a flat base slipped under the roofing and a rubber or metal sleeve that grips the pipe.
On a flat roof. The membrane runs up the parapets and walls to form an upstand. Metal coping caps the top of the low wall, and a counter-flashing protects the top of the upstand.
Why leaks start there
Roofing laid over an open surface has few reasons to leak. A joint between two materials has several.
- Materials move. Brick, wood and metal each expand at their own rate. Between summer and winter, the joint works constantly.
- Sealant ages. The product that closes the top of a counter-flashing dries, cracks and peels long before the roof reaches the end of its life.
- Rubber dries out. The sleeve of a vent boot splits in the sun.
- Mortar crumbles. A counter-flashing set into a brick joint loses its anchor when the joint empties.
- The installation was faulty. Flashing that is too short, nailed in the wrong place or simply buried in sealant holds for a few years, then fails.
- The old flashing was reused. When a roof is redone, keeping the old flashing saves time. The new roof then inherits the weak point of the old one.
Repairing flashing
There are three levels of work.
- Redo the sealant. This is quick and inexpensive, but it is maintenance. It will need doing again.
- Replace the piece. A vent boot or a section of flashing can be changed without touching the rest.
- Redo the whole detail. Around a chimney, the step flashing and the counter-flashing are redone, with the counter-flashing properly set into the masonry.
Frequently asked questions
How do I know if my flashing is the problem?
A ceiling stain near a chimney, an exterior wall or a vent pipe points to flashing. A leak that only appears in rain with wind is another clue. Only an examination on the roof confirms it.
Should flashing be replaced with a new roof?
Yes, replacing the flashing with the roof is strongly recommended. Flashing rarely has a second life as long as the new roofing. Ask for it to be written in the quote.
Is redoing the sealant every year enough?
Redoing the sealant extends the life of flashing in good condition, but it does not save metal that is pierced, too short or badly installed. If the sealant has to be redone often in the same spot, the problem is elsewhere.