What Is Chimney Flashing?
A chimney is the most common leak point on a shingle roof because four kinds of flashing have to work together. Step flashing runs up each side, one piece per shingle course, woven so water steps down and out. An apron flashing seals the low side. On the high side, where water and debris collect, a cricket (a small peaked diverter, required by code above a certain chimney width) or at least a back pan carries water around. Over all of these, counter flashing is cut into the mortar joints and bent down to cover the tops of the base flashings, so water running down the brick cannot get behind them. Common failures are counter flashing that is surface-mounted and caulked instead of let into the masonry, step flashing skipped in favor of a single L-shaped piece, and a missing cricket. Caulk is not flashing; a chimney that leaks after 'sealing' usually needs the flashing rebuilt.
Important Distinction
Note: This describes the component in general. Which product, gauge or detail a specific roof needs is a job-by-job determination made after an inspection, and the building code and the manufacturer's installation instructions govern over any general description.
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Also Known As
These are the search terms and phrases that commonly refer to this topic, so you can find it however you describe it.
How Chimney Flashing Relates to Other Topics
An apron flashing seals the low side of the chimney.
A cricket above the chimney diverts water and debris around it.
Counter flashing let into the mortar covers the tops of the base flashings.
Chimney flashing is the most common leak point on a shingle roof.
Step flashing runs up each side of the chimney, one piece per course.
Questions about Chimney Flashing?
Zilker Roofing inspects before recommending. Honest assessment, no pressure.