Chimney Leaks: Where the Water Gets In and How It's Fixed

A stain on the ceiling next to the fireplace, or water in the attic around the chimney, is one of the most common roof leaks there is. The chimney gets blamed, but most of the time the water is getting in where the chimney meets the roof.

Why chimneys leak

A chimney is a big masonry box cut through the roof. The roof and the chimney move differently with heat, cold and settling, so the joint between them has to be sealed with flashing that allows for that movement. When that seal fails, water runs down the outside of the chimney and into the house.

1. Failed flashing

Chimney flashing is metal worked into the roof and the brick in layers:

• Step flashing runs up the sides, woven in with each row of shingles.

• Counter flashing is set into the mortar joints and laps over the step flashing.

• The apron covers the front, on the low side.

• The back (the high side) takes the most water, because everything running down the roof hits it.

Flashing rusts, pulls out of the mortar joints, or gets nailed or sealed wrong in the first place. Sealant smeared over the joint is a common shortcut. It cracks within a few seasons and the leak comes back.

The fix: remove the old flashing and install new step flashing, counter flashing and apron, properly lapped and set into the mortar. This is roofing work.

2. No cricket behind a wide chimney

On the high side of a chimney, water and leaves pile up against the brick. A cricket (also called a saddle) is a small peaked roof behind the chimney that splits the water around it. The International Residential Code requires one on any chimney more than 30 inches wide. Older houses often don't have one.

The fix: a cricket is usually added when the roof is replaced. Until then, the back flashing needs to be in good shape and kept clear of debris.

3. A missing or damaged chimney cap

The flue cap covers the top of the flue liner and keeps rain, animals and debris out. Without one, rain falls straight down the flue. A rusted or damaged cap does the same.

The fix: replace the cap. It's a small job that stops a lot of water.

4. Cracked crown or brick

The crown is the concrete or mortar slab on top of the chimney around the flue. When it cracks, water soaks into the brick below. Porous brick, missing mortar and spalling (brick faces flaking off) let water in through the chimney itself.

The fix: this is masonry work for a mason or chimney professional. If the flashing is sound but the chimney is still wet, the masonry is the likely cause, and we'll tell you so.

How to tell where the water is coming from

From inside and from the ground, a few clues help:

• Leaks only in heavy, wind-driven rain usually point to the flashing on one side.

• Water inside the firebox or on the damper points to the cap or the crown.

• White staining (efflorescence) on the brick outside or in the attic means water is moving through the masonry.

• Stains on the ceiling beside the chimney often mean the back or the sides.

• Rusted or loose metal at the base of the chimney, visible with binoculars, is a flashing problem.

Don't climb onto the roof to check. Chimneys sit high, and the roof around them is often steep.

Before fireplace season

If you use a fireplace or wood stove, have the flue checked by a chimney sweep before the first fire. Have the roof side of the chimney checked too: flashing, cap and cricket. A leak around a chimney soaks the framing and the drywall long before it shows as a drip.

Common questions

Can I just seal around my chimney to stop a leak?

Sealant can stop a drip for a while, but it isn't flashing. It cracks with the first few freeze-thaw cycles, and the leak returns. A lasting fix is new flashing, lapped and set into the mortar.

Is a chimney leak a roof problem or a chimney problem?

Usually a roof problem. Most chimney leaks come from the flashing where the chimney meets the roof. If the flashing is sound, the crown or the brick is the next suspect, and that's masonry work.

Should chimney flashing be replaced with a new roof?

Yes. Reusing old chimney flashing under new shingles is a common reason a new roof leaks. New step and counter flashing should go in with the new roof.

Does my chimney need a cricket?

If it's more than 30 inches wide, the building code requires one on the high side. Many older homes don't have one, and adding it during a roof replacement is the simplest time.

Get your chimney leak checked

3 Peaks Roofing repairs chimney flashing and replaces flue caps on homes across Louisville, Jefferson and Bullitt counties, La Grange and Southern Indiana. Our free roof inspection covers the flashing, the cap and the roof around the chimney, with photos of what we find. Learn more about roof leak repair and roof repair, or call 502-864-7663 (Monday to Saturday, 7 AM to 5 PM) or request an inspection.