Part H · the register

Your Kirkwood Chimney Crown Cracks Before the Roof Does

Kirkwood's freeze-thaw winters open cracks in chimney crowns, and the water finds the flue and the brick below. Here is what to check this fall.

A chimney crown is the cap of concrete or mortar at the top of a masonry chimney, sloped so rain runs off and away from the flue opening. In Kirkwood, where many older houses have brick chimneys that have stood through decades of freeze-thaw cycles, that cap is often the first part of the house to crack. A crack in the crown is small and easy to overlook from the yard, but water that gets into it does not stay at the top. It runs down into the brick, into the gap between the crown and the flue tile, and into the attic and the wall below.

This page is for the homeowner who is deciding this fall whether a chimney needs attention before the first hard freeze, and who wants one specific thing to look for. The answer is usually a crack, a gap, or a pale stain, and each one points to a different next step.

Why the crown fails first

Brick is porous. When it takes on water and that water freezes, it expands, and the face of the brick flakes or pops away. This is called spalling, and in St. Louis winters it can move quickly once the top courses start to go. The crown sits in the most exposed position on the house, with no shelter from the roof above it, and it catches rain from every direction. A mortar crown that was troweled with a thin edge will crack at that edge first. A concrete crown that has shrunk away from the flue liner leaves a seam that rain follows straight down.

Older Kirkwood chimneys also tend to have crowns that were never designed to shed water well. Some are nearly flat. Some have been patched over the years with a different mortar that does not bond the same way, so the repair sits on top of the old crack instead of replacing it. The result is a crown that looks solid from the sidewalk and leaks in the first hard rain.

What to look for from the ground

Start from the yard, on a dry day, with the sun behind you if you can manage it. Look at the top of the chimney and then at the brick just below it. Note these things, in this order:

• Hairline cracks running across the crown, especially ones that reach the edge.
• A gap between the crown and the flue tile, which can show as a dark line where the chimney meets the cap.
• Missing or broken mortar on the top three or four courses of brick.
• White, chalky staining on the brick below the crown. This is efflorescence, the salt left behind when water moves through masonry and evaporates.
• Rust streaks running down from a metal cap, a damper, or a flue fitting.
• Brick faces that have popped or flaked, particularly on the side facing the prevailing weather.

A pair of binoculars is enough for most of this. Take photographs at the same time, from the same spot, so you can see whether the cracks are getting longer from one season to the next. Date each file. This is the same habit that helps with any roof question: a dated photo is worth more than a memory of what the chimney looked like.

What the roofline shows

The roof covering around the chimney is part of the same question. The flashing where the chimney meets the roof is a separate detail, and a crown can look sound while the flashing beside it has lifted. If you see stains on the ceiling near the chimney wall, or on the wall of the room the chimney passes through, the water may be coming from the flashing rather than the crown, or from both. Do not assume the crown is the cause until someone has looked at the flashing too.

Any work on the roof surface around a chimney means a ladder, and a steep roof with wet leaves is not a place for a homeowner to inspect. Let a roofer walk it. A roofer who looks at the crown should photograph it from several sides, measure any open crack or gap, and put what they found in writing, with the photographs attached. That written record is useful to you whether you hire them or not.

Where a roofer's work ends and a mason's begins

A roofer can flash a chimney, replace a metal cap, reset a damaged flue fitting that sits in the roof, and inspect the crown as part of the roof review. Repairs that are really masonry, such as rebuilding the top courses, repointing the brick, or casting a new crown, often belong to a mason. Some jobs are both, and the line between them is the first thing to settle in the proposal. A written scope should name the masonry work on its own line, so it is not hidden inside a roofing total.

Ask the roofer who will do the masonry, and whether that person is a separate contractor, a subcontractor, or a crew member on the roofer's own payroll. The answer tells you who to call back when the repair cracks again.

Permits in Kirkwood

Kirkwood issues its own building permits, and whether a chimney repair needs one depends on how much of the structure is being changed. Replacing a cap or repointing a few courses may not trigger the same review as rebuilding the chimney above the roofline. Ask the city's building division before work starts, and ask the contractor to state in the written scope whether they have checked. A permit that is pulled late can leave a finished job with an open question on the record, and that matters when you sell the house.

What it costs, in general terms

The cost of a crown repair depends on the size of the chimney, how high it sits above the roof, how much brick has to be taken down and rebuilt, and whether a metal cap or a new flue fitting is part of the job. A simple crown patch on a short chimney is a small line item. A rebuilt crown on a tall chimney with spalled brick is a different job, and the difference should be visible in the scope. If two proposals put very different numbers on the same chimney, compare the lines before you compare the totals. One may include a new crown while the other only seals the existing one.

Timing affects the price too. Masonry mortar does not cure well in very cold weather, and a crown patch done in a hard freeze may need protection or may have to be redone. Ask each roofer how they handle cold-weather masonry work, and whether the price changes if the crew has to wait for a warmer stretch.

What to ask before you choose

• Which part of the chimney is being repaired, and which part is being replaced?
• Who does the masonry, and is it in the same written scope as the roofing?
• Does the flashing get inspected at the same visit as the crown?
• What will the scope and photographs show when the job is finished?
• Does Kirkwood need a permit for this work, and who pulls it?
• If water shows up in the room below the chimney after the first storm, who comes back, and how is that visit scheduled?

Keys Roofing can be reached at (314) 220-2333 to talk through a chimney in Kirkwood before the first hard freeze. Call with the photographs you took from the yard, and say which part of the chimney worries you most.