How does Minnesota's freeze-thaw cycle damage a chimney crown?

Minneapolis Fireplace & Chimney · November 4, 2026

Where the 75 comes from

NOAA publishes 1991–2020 climate normals for weather stations across the metro. For the MSP airport, the normals show about 147 nights a year when the low drops to 32°F or below, and about 72 days when the high never gets above freezing. Subtract the second number from the first and you get roughly 75 days a year that freeze at night and thaw during the day. That is our own arithmetic on two NOAA fields, not a figure NOAA reports, but it gives a fair sense of the strain on outdoor masonry.

The number climbs north of the cities. At the Andover station in Anoka County, the same subtraction gives roughly 90 days, along with about 39 nights a year at or below zero compared with about 22 at MSP. Homes in Andover, Anoka and nearby towns likely see more of these cycles than homes along the river in Minneapolis.

What a crown is supposed to look like

The current Minnesota Residential Code follows IRC R1003.9.1: masonry chimneys shall have a concrete, metal or stone cap, sloped to shed water, with a drip edge and a caulked bond break around any flue liner. Masons call that cap the crown.

Each part has a job. The slope sends water off the top instead of letting it pool. The drip edge, an overhang with a groove or lip underneath, lets water fall clear instead of running down the brick face. The bond break lets the flue tile and the crown expand at different rates without cracking each other.

• A flat crown that holds puddles after rain.
• A thin wash of mortar troweled over the top bricks, with no overhang.
• Hairline cracks radiating out from the flue tiles.
• Chunks missing from the corners, or a crown you can see sitting loose.
• Rust-colored or white staining running down the upper bricks.

How the damage builds

A thin mortar wash is the most common crown on older Twin Cities houses, and it is the one that fails first. Once water gets into a crack, each freeze pushes the crack a little wider. Water then reaches the bricks and mortar joints below, and the same freeze-thaw cycle starts to pop the faces off the brick, which masons call spalling.

Extreme cold adds stress of its own. The MN DNR climate office records a low of −28°F at MSP on January 30, 2019, with wind chills near −55°F. A wet crown going through a stretch like that, then into a February thaw, is how a small crack becomes a loose slab.

Repair or replace

If the crown is sound with only fine cracks, a crack repair with a flexible crown sealer can add years. That typically runs $200–$700+. If the crown is flat, has no drip edge, is broken through or loose, or the bricks under it are already spalling, replacement is the better buy. A new crown formed with a proper slope, drip edge and bond break typically runs $1,000–$3,000.

A cap with a screen over the flue keeps rain and snow out of the chimney itself and protects the new crown around the tiles. A cap installed runs $200–$850. A breathable water repellent on the brick below, $150–$820+, helps the masonry dry out between freezes.

When to have it looked at

Late summer and early fall are the best time, before the first hard freeze. A crack that is open in October will be worse by April. Our inspection is free: we go up on the roof, photograph the crown, the flue tiles and the top courses of brick, and give you a written price for what needs doing.