Chimney flashing is the metal seal where the chimney meets the roof. Proper flashing has two layers: step flashing woven into the shingles and counter flashing cut into the mortar joints over it. Flashing that is only caulked or glued to the brick is the most common cause of chimney leaks.
How flashing works
Step flashing is L-shaped pieces of metal layered with each row of shingles along the sides of the chimney. Counter flashing is set into a cut in the mortar joint and folds down over the step flashing, so water can't get behind it. The front gets an apron and the uphill side usually gets a cricket (a small peaked diverter) on wider chimneys.
Signs your flashing has failed
- Water stains on the ceiling or walls next to the chimney
- Rusted, lifted or bent metal at the base of the chimney
- Thick layers of tar or caulk smeared over the joint
- Leaks only during heavy or wind-driven rain
Why caulk-only repairs fail
Brick and metal expand and contract at different rates. Caulk alone cracks within a season or two, and water gets back in. Counter flashing cut into the mortar is the lasting fix.
More questions
Can I fix chimney flashing with roofing tar?
Tar can slow a leak temporarily, but it cracks with temperature changes. Properly installed step and counter flashing is the permanent fix.
Need a local professional?
Chimney Champs has been a local chimney company for 13 years. We provide chimney waterproofing & leak repair in your area. Call (856) 300-9215 for a free estimate.
Sources & further reading
- NFPA 211 — Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances (National Fire Protection Association)
- Chimney Safety Institute of America (CSIA)
Keep reading
- 9 Signs Your Chimney Needs Repair
- Why Is My Chimney Leaking? 6 Causes and How to Fix Them
- Chimney Crown vs. Chimney Cap: What's the Difference?
- Flaking Brick and White Stains on Your Chimney: What They Mean
- Prefab Fireplaces and Rusty Chase Covers: A Guide for Newer Homes
- How Often Should You Clean Your Chimney?