Know Your Roof · Flashing & Roof Edge

Chimney Flashing: Parts and Common Leaks

Quick answer

Chimney flashing is the set of metal pieces that seals the joint between a chimney and the roof. It works in layers: base flashing, step flashing, and counter flashing set into the masonry, often with a cricket on the uphill side. If any layer fails, water gets into the roof and the chimney.

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Roofer working on flashing at a brick chimney in Greater Cincinnati

The parts

Base (apron) flashing sits at the downslope face of the chimney. Step flashing runs up the sides, stepped with the shingles. A back pan or cricket on the uphill side splits the water around the chimney. Counter flashing is set into the mortar joints and laid over the base flashing.

What a cricket is

A cricket (or saddle) is a small peaked structure behind a chimney that diverts water around it. Building codes typically call for one on wide chimneys, often anything over 30 inches wide, but check your local requirements.

Why chimney flashing leaks

  1. Cracked mortar where the counter flashing is set
  2. Rust or lifted metal
  3. Sealant that dried out
  4. No cricket on a wide chimney
  5. A cracked chimney crown or masonry, which is a different leak path with the same signs

Why the masonry matters

Cincinnati has plenty of older brick chimneys. Mortar that's breaking down needs tuckpointing, so the counter flashing has something solid to seal into.

What does chimney flashing repair cost?

Chimney flashing is repaired or rebuilt around the chimney, often with a cricket. Flashing repair around a wall, chimney, or valley typically runs $400 to $900. A minor repair that includes flashing, a vent boot, or one or two shingles runs $400 to $750. The final number depends on how much flashing is damaged and how hard it is to reach, and every job starts with a free roof inspection.

Looking for another word? See the roofing terms glossary, A to Z.

FAQ

Chimney Flashing: common questions

How do I know if my chimney flashing is leaking?

Stains on the ceiling or wall near the chimney, especially after wind-driven rain.

Can chimney flashing be repaired, or does it need replacing?

Small gaps can be sealed, but most real leaks need the metal relaid.

Is chimney flashing covered by a roof warranty?

It depends on the warranty. Get the terms in writing.

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Related terms

  • Step Flashing

    Step flashing is a series of small L-shaped metal pieces installed in a stair-step pattern where a sloped roof meets a vertical wall, like a dormer or the side of a chimney. Each piece overlaps the shingle course below it, so water is led down and out over the shingles instead of into the joint.

  • Counter Flashing

    Counter flashing is a second piece of flashing installed over the top edge of the base flashing, usually set into a wall or the mortar of a chimney. It blocks water from sneaking behind the base flashing, and it lets the roof and wall move a little without breaking the seal.

  • Apron Flashing

    Apron flashing is a long piece of bent metal that seals the joint where a roof slope runs up into a vertical surface, like the front of a chimney, a dormer face or a wall at the top of a slope. It sheds water running down that wall onto the roof, and counter flashing or siding covers its top edge.

  • Roof Flashing

    Roof flashing is thin metal, sometimes rubber, installed wherever a roof meets something else: a chimney, a wall, a vent, a valley. It steers water over those weak spots and away from the roof deck. A lot of roof leaks start at flashing, not in the middle of the shingles.

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