Chimney Leaking When It Rains? The 4 Places Water Gets In

A drip in the firebox, a damp smell after a storm, a brown stain spreading on the ceiling beside the chimney. Chimney leaks are easy to put off, because they come and go with the weather. That is the problem with them. The Chimney Safety Institute of America says "water causes more damage to masonry chimneys than fire," and that it "is usually a slow process which is easily ignored until problems have become quite serious."

1. The cap: water straight down the flue

What you see: water or dampness in the firebox soon after rain, and a rusty damper. Why: a chimney with no cap, or a damaged one, is an open hole pointing at the sky. The fix: a properly fitted cap. The CSIA lists it first among its four ways to prevent chimney water damage. See do you need a chimney cap?

2. The crown: water into the top of the chimney

What you see: cracks in the concrete slab at the top of the chimney, loose or damaged brick in the top few rows, dampness inside the chimney itself. Why: the crown seals the top of the masonry around the flue, and once it cracks, rain runs into the core of the chimney. The fix: small cracks are sealed; a crown that is breaking up is rebuilt. The CSIA says a crown should project two inches beyond the chimney on all sides, so water drips clear of the brick.

3. The flashing: water where the chimney meets the roof

What you see: a stain on the ceiling or wall right beside the chimney, or wet wood around the chimney in the attic. Why: flashing is the metal seal between the roof and the chimney. When it fails, the CSIA notes, rainwater runs down the chimney into the house, where it can damage ceilings and walls and rot rafters and joists. The fix: the flashing is repaired or replaced.

4. The brick and mortar: water through the walls

What you see: white, chalky staining on the outside of the chimney, brick faces flaking off, mortar crumbling out of the joints. Why: in the CSIA's words, "common brick is like a sponge, absorbing water and wicking moisture to the chimney interior," and worn mortar joints make it worse. The fix: failed mortar is cut out and replaced (tuckpointing), damaged bricks are replaced, and a masonry water repellent goes on afterward.

A fifth one, if your fireplace is prefab

Many newer Triangle homes have a factory-built fireplace that vents through a framed, sided chase, not a brick chimney. The top of that chase is sealed with a metal chase cover. When the cover rusts through, water gets into the chase. Rust streaks running down the siding below the chimney top are the giveaway.

Why it is worse in the Triangle than you would think

Raleigh gets rain in every season, so a leak never gets a long dry spell to hide in. And on winter nights that drop below freezing, the water already inside the brick and mortar expands and widens the cracks it came in through. A small leak in October is usually a bigger one by March.

How we handle it

Guessing gets expensive, because the stain inside is often several feet from where the water gets in. We start with a $69 professional inspection of the cap, crown, flashing, brick and flue, photograph what we find, and give you a written price for the repair before any work starts. The details are on our chimney & fireplace repair page.

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