How do Chicago freeze-thaw days damage a chimney crown?

Chicago Chimney & Fireplace Repair · November 4, 2026

Where the 78 comes from

NOAA's climate normals for O'Hare list an average of 121.3 days a year with a low at or below 32°F, and 43.4 days with a high at or below 32°F. Subtracting the second from the first gives about 78 days when the temperature crosses the freezing line in both directions. That is our own calculation from two NOAA figures, not an official NOAA count.

The same method gives about 67 days at Midway, which sits in a warmer, more built-up part of the city, and about 86 at Rockford, farther inland. O'Hare also averages 38.4 inches of snow a year and about six nights at or below zero. A Chicago chimney sees many cycles each winter, wherever it stands.

What a crown does and how it fails

The crown is the cap of concrete or mortar across the top of the chimney, around the flue tile. It is meant to shed water away from the brick and seal the gap between the masonry and the flue. On many older Chicago chimneys it was never a proper crown at all, just a thin wash of mortar sloped toward the edges.

Water gets into hairline cracks, freezes and opens them a little wider. Snow sitting on a flat or shallow crown melts in the afternoon sun, soaks in and freezes again overnight. Over a few winters, the crack becomes a gap, the crown loosens from the flue tile, and water starts running down inside the chimney.

• Hairline or open cracks across the top surface.
• Pieces of crown on the roof or in the gutter.
• A gap where the crown meets the flue tile.
• Brick below the crown flaking or losing mortar.
• Water stains or a damp smell at the fireplace after rain or snowmelt.

Repair, rebuild or start over

Small cracks can often be repaired and sealed. Minor crown repairs usually run $150 to $700. Larger cracks, loose edges or a crown that needs resurfacing usually run $600 to $1,500 or more. A new poured crown, built to current code with an overhang that throws water clear of the brick, usually runs $1,000 to $3,000.

A crown that has already let water into the top courses often needs some brick reset as well. If the damage goes deeper, rebuilding the top few feet of the chimney with a new crown usually runs $600 to $1,000.

Why fall is the time to look

A crack that is easy to fix in October can turn into loose brick by March. Once snow and ice are on the roof, the work gets harder and the damage keeps going all winter. A cap over the flue helps too, keeping water and debris out of the flue itself.

Our inspection is free. We look at the crown up close, photograph it, and give you a written price. We work Sunday to Friday in 3-hour arrival windows and call to confirm before we come.