Short answer: most chimney leaks come from failed flashing or a cracked crown, not from the chimney structure itself. Check flashing, crown, cap and mortar before you light the first fire of the season.
If we are called out for a leak on an older Boerne or San Antonio home, the chimney is the first place we look. It interrupts the roof plane, it is made of a different material that moves differently, and it usually has the oldest flashing on the building.
The five failure points
- Step flashing. Individual metal pieces woven into each shingle course along the chimney sides. When someone caulks instead of installing step flashing, it fails within a few years.
- Counterflashing. The metal that laps over the step flashing and is cut into the masonry. On Hill Country limestone, surface sealing it instead of cutting it in is a fast failure.
- The cricket. A small peaked structure behind a wide chimney that diverts water around it. Chimneys wider than about 30 inches need one. Plenty of homes here do not have one and should.
- The crown. The concrete or mortar slab on top. Cracks let water into the chimney body, where it freezes, expands and widens the crack.
- The cap. The metal lid with mesh. Missing caps let rain, animals and debris straight down the flue.
Why Hill Country chimneys have it worse
Limestone and native stone are beautiful and they are porous. Mortar joints on stone chimneys weather faster than people expect, and the temperature swings here are hard on masonry. A 70 degree afternoon followed by a 32 degree night moves materials in ways that steady climates do not.
Historic homes in downtown Boerne frequently have original masonry chimneys with flashing that has been patched by several generations of different approaches. We wrote about that in roofing historic Boerne homes.
What to check before the first fire
- Water stains on the ceiling or wall near the chimney, inside or in the attic
- White chalky residue on the masonry, which means water is moving through it
- Visible gaps, lifted metal or heavy caulk at the roofline
- Crumbling mortar joints or spalling brick face
- A missing or damaged cap
- Rust stains running down from the flashing
- A damper that will not seat properly, which can indicate moisture damage
Roofing versus chimney sweeping
Two different trades and both matter before you burn anything.
A chimney sweep handles the flue, creosote buildup and draft safety. That is a fire safety issue and it is genuinely important if you burn regularly.
We handle the exterior water side: flashing, cricket, crown sealing, cap and the roof interface. If you are about to start a season of fires, both are worth doing.
Do it with your roof if you can
If a replacement is coming, chimney flashing should be rebuilt as part of it rather than reused. Reusing old chimney flashing on a new roof is one of the most common shortcuts we find, and it leaks within a few years on an otherwise good roof.
Ask any contractor directly whether new chimney flashing and counterflashing are in the scope. If the answer is vague, it is not in the scope.
Free inspection includes the chimney
We photograph the chimney, flashing and crown on every inspection and tell you what we see. Book one or call (210) 245-4125.
