Why Is My Chimney Leaking Water?
Water around a chimney comes from one of five places. Where the water shows up tells you which.
The likely causes
There are five common causes. The table shows how to tell which one you have.
| Cause | How to tell | What fixes it |
|---|---|---|
| Missing or damaged cap | Water or rust in the firebox after rain. | Fit a cap sized to the flue. |
| Cracked crown | Water in the firebox, damp brick near the top of the stack. | Seal small cracks; rebuild a crown that is crumbling. |
| Failed flashing | Stains on the ceiling or wall next to the chimney, or water in the attic. | Reseal or replace the flashing where the chimney meets the roof. |
| Porous brick and mortar | Damp patches on the chimney inside the house, white staining outside. | Tuckpoint worn joints and apply a breathable water repellent. |
| Condensation in the flue | Dampness with no rain, usually on a flue serving a gas appliance. | Reline the flue to the correct size for the appliance. |
What to do right now
Put a container under any drip and note when the water appears: during rain, after rain, or in dry weather. That timing is the most useful thing you can tell a sweep.
When to call a professional
Call a sweep promptly for any chimney leak. Water damage gets more expensive every winter it is left, because trapped water freezes and breaks up the masonry.
Want it looked at?
Call (816) 239-8989Related pages
These pages cover the services that deal with this problem: chimney repair, chimney inspection, chimney anatomy diagram. For the full picture, read our chimney care guide.
Common questions
How do I know if the leak is the chimney or the roof?
Look at where the stain is. A stain directly beside the chimney, on the ceiling or wall, usually means the flashing between the chimney and the roof. A stain well away from it is more likely the roof itself. A sweep can water-test the chimney to confirm.
Can a chimney leak cause mold?
Yes. Water that soaks into the masonry, the framing around the chimney or the attic insulation stays damp for a long time, and mold can grow there. Fixing the leak comes first; damp materials then need to dry out or be replaced.
What is efflorescence on a chimney?
Efflorescence is the white, powdery staining left on brick when water moving through the masonry evaporates and leaves salts behind. It is a sign that water is getting into the chimney. Cleaning it off does not solve anything until the source of the water is found.
Should a chimney be waterproofed?
A breathable water repellent made for masonry can help an older chimney shed rain while still letting moisture escape. Ordinary sealers and paint trap water inside the brick and make the damage worse. Repairs to the crown, cap, flashing and joints come before any repellent.
Does homeowners insurance cover a leaking chimney?
It depends on your policy and the cause. Insurers generally treat sudden damage, such as from a storm or lightning, differently from gradual wear. Check your policy and ask your insurer. An inspection report describing the cause is useful either way.