Chimney Crown Repair and Replacement

No part of a chimney takes more weather than the crown. It sits flat on top of the stack, catches every inch of snow and rain, and freezes and thaws all winter. NOAA's 1991 to 2020 normals for O'Hare show about 121 nights a year at or below freezing but only about 43 days that stay below freezing all day. Subtract one from the other and you get roughly 78 days a year that freeze at night and thaw in the afternoon. That number is our calculation from NOAA's figures, not an official count, but it explains why Chicago crowns crack.

It also varies across the metro. By the same math, Midway comes out near 67 such days and Rockford, inland, near 86. Minor crown repair typically runs $150 – $700. Major repairs with large cracks or reset brick run $600 – $1,500+. A new poured crown with a drip edge typically costs $1,000 – $3,000. The inspection is free.

Signs you need this

• Cracks across the top of the chimney, visible from a ladder or a photo
• Bits of concrete or mortar on the roof or in the gutter
• A crown flush with the brick, with no overhang at all
• Flaking brick or stains in the top few courses
• A cap or damper rusting where it sits on the crown

How we do it

1. Inspect up closeWe check the crown's slope, overhang and cracks, and whether water has reached the brick below.
2. Repair or replaceA sound crown with surface cracks gets a crack sealer; a broken or crumbling one is taken off.
3. Form and pourA new crown is formed with an overhang and drip edge, with a bond break around the flue tile, and poured in concrete.
4. Seal the flue jointThe gap between flue tile and crown is sealed with a flexible high-temperature sealant so water can't get in.

How freeze-thaw breaks a crown

Water gets into hairline cracks in the crown on a mild afternoon. Overnight it freezes and expands, pushing the crack a little wider. Next day the crack holds a little more water. Repeat that about 78 times in a winter and a hairline becomes a gap you can slide a coin into, then a loose piece.

Lake-effect storms add to it. When a band drops several inches of wet snow on a north-shore chimney, all of it eventually melts across the crown.

Why so many old crowns fail early

On many older Chicago chimneys, the crown isn't really a crown. It is a few inches of mortar troweled over the top course, flush with the brick and sloped by eye. With no overhang, water runs straight off the edge and down the face of the top courses, which is why we so often find a band of spalled brick just under the crown and sound brick below.

A new crown is poured in concrete, sloped to shed water, extended past the brick with a drip edge underneath, and kept separate from the flue tile so the two can move independently. It is built to current code.

Can a cracked crown just be sealed?

If the crown is solid and the cracks are fine, a flexible crown sealer bridges them and buys several years. Sealer won't save a crown that is loose, crumbling or has no overhang. We'll tell you which you have, with photos, and won't sell you a new crown when sealing is enough.