The Chimney

The parts and how they fail

Step flashing up each side, woven into the shingle courses. Frequently reused from the previous roof and no longer sound.

The base or apron flashing at the downslope face.

A cricket or saddle behind a wide chimney, which diverts water around it. On many Toronto houses it was never built, and water sits behind the chimney instead.

Counter flashing let into a mortar joint and sealed, which is what keeps water out of the top of the step flashing. Surface-mounted counter flashing with caulk is the common shortcut.

The masonry itself, because a chimney with deteriorated mortar or a failed crown absorbs water and the leak is not the flashing at all.

And the crown and the cap, which if cracked or missing lets water into the flue and the masonry from above.

Caulk is not flashing

A line of roofing cement or caulk where the chimney meets the roof is the single most common thing found on a leaking chimney in Toronto. It works for a season, cracks over a winter, and then holds water in the joint. Proper flashing is metal in layers, and it is the repair.

Working out which it is

A leak that appears in rain with wind from one direction points at the flashing on that face.

A leak after prolonged rain rather than during it suggests the masonry absorbing and releasing inward.

Staining inside the firebox or on the chimney breast suggests the crown or the cap.

Staining on the ceiling beside the chimney suggests the flashing.

White staining on the brick outside is efflorescence, which means water is moving through the masonry.

And the attic is where to look first, up-slope of any stain, during or just after rain.

The repair

New step flashing, woven into the shingle courses properly, which means lifting the courses rather than surface-mounting it.

A cricket where the chimney is wide enough to need one.

Counter flashing cut into the masonry joint and sealed, rather than surface mounted with caulk.

Masonry work where the mortar or the crown has failed, which is a different trade and is frequently the actual cause.

A cap, which keeps water and animals out of the flue.

And doing it at the same time as a reroof where possible, because new flashing woven into new shingles is both cheaper and better than retrofitting it later.