How does lake-effect snow cause chimney leaks?

Chicago Chimney & Fireplace Repair · November 10, 2026

What happened in November 2025

The National Weather Service office in Chicago reported that lake-effect bands on November 9 and 10, 2025 brought locally significant snow, up to about a foot in places, with snowfall rates above 2 inches an hour in the strongest bands, including in Lake County. There were several reports of thundersnow near the lake early on November 10.

The totals varied block by block. The NWS listed 10.0 inches in Winthrop Harbor, 5.7 inches in Chicago's West Ridge, 5.2 inches in Evanston, 5.1 inches near Mundelein, 5.0 inches in Gurnee and 5.0 inches near Villa Park. O'Hare's official total was 1.7 inches, and the weather service noted a gap between the two main bands over Chicago and nearby suburbs.

Lake-effect snow does not hit the same towns every winter. It does mean a roof can go from bare to buried in a single night, which is the hard part for a chimney.

Where the water gets in

Snow drifts against the uphill side of a chimney, and it sits there. On sunny afternoons it melts at the edges and the water runs down along the brick. Wherever the flashing has lifted, cracked or pulled out of the mortar joint, that water goes under the shingles and into the attic or the ceiling below.

• Step flashing along the sides that has rusted or come loose.
• Counter-flashing, set into the brick joints, whose mortar has washed out.
• The uphill side of a wide chimney, where snow and water collect.
• Caulk used as a shortcut in place of proper flashing, now dried and cracked.
• A cracked crown or missing cap letting water straight down inside the chimney.

Signs to look for after a heavy snow

Leaks around a chimney often show up a day or two after the snow, once the melt starts. Look for water stains on the ceiling or wall next to the chimney, damp wood in the attic near the stack, peeling paint around the fireplace, or a musty smell from the firebox. Rust on the damper or water at the base of the fireplace usually points to the top of the chimney rather than the flashing.

What repairs cost

Typical 2026 ranges: flashing repair runs $300 to $1,800 depending on the size of the chimney. Sealing a specific leak usually runs $150 to $500. Breathable waterproofing for the brick runs $150 to $820 or more. If the crown is part of the problem, minor crown repairs run $150 to $700.

The fix depends on where the water is coming from, so we find that first. Our inspection is free and includes photos and a written price.

Gas vents and snow

The same storms can bury side-wall gas vents for high-efficiency furnaces and water heaters. Nicor Gas warns that snow or ice over a gas vent can cause carbon monoxide to build up indoors, and it recommends clearing vents by hand or with a broom rather than a shovel. If the vent is under a drift, clear it before you worry about the chimney.