The crown is the sloped concrete slab covering the whole top of the brickwork; the cap is the metal lid with mesh sides that sits over the flue opening itself. They fail differently and cost differently: cap installation starts at $159, while crown repair starts at $319 and a full rebuild is quoted after inspection. If water is getting into your chimney, the crown is the more likely culprit, and it is the one nobody ever looks at.
Two parts, two jobs
Stand back and look at the top of a masonry chimney. The flue tile usually projects a few inches above everything else. Around it, covering the entire top surface of the brick, is a flat or gently sloped slab. That slab is the crown. Its job is to shed water off the top of the masonry and away from the brick, ideally with an overhang and a drip edge so runoff falls clear of the wall instead of down the face of it.
Sitting on top of the flue tile, or bolted to it, is the cap: a metal roof on legs with mesh screening between them. Its job is to keep rain, snow, leaves, birds and squirrels out of the flue opening, and to keep sparks from landing on your roof.
They protect different things. The cap protects the inside of the flue. The crown protects the masonry structure the flue runs through. A chimney with a perfect cap and a shattered crown is still soaking up water, and the damage from that is slower, more expensive and harder to see. Prefabricated chimneys, the ones inside a framed and sided chase, have a metal chase cover in place of a masonry crown, which is a different part with its own failure pattern.
How a crown fails, and why so many were built to
A properly built crown is a poured concrete slab, reinforced, several inches thick, sloped away from the flue, extending past the brick with a drip edge, and separated from the flue tile by a flexible expansion joint so the two can move independently.
What sits on top of most chimneys in the western suburbs is none of that. It is a thin layer of mortar troweled flat across the brick and up against the tile. Mortar is not concrete: it is not reinforced, it is not designed to be a horizontal weather surface, and it is nowhere near thick enough. It cracks, generally within the first ten to fifteen years.
Then the freeze-thaw cycle takes over. Water gets into the crack, freezes overnight, expands and widens the crack. Repeat that through an Illinois winter and a hairline turns into a gap you can put a screwdriver into. Water runs straight through it into the top course of brick.
The second common failure is the joint against the flue tile. Clay tile and masonry expand at different rates when heated. Without an expansion joint, the crown cracks in a ring right where it meets the tile, and every drop of rain that lands on that surface funnels directly down the outside of the liner into the chimney’s interior.
The third is the missing overhang. A crown poured flush with the brick face dumps its runoff straight down the wall, which saturates the brick and mortar joints continuously. That is what eventually produces spalling faces, crumbling joints, and the white mineral staining that shows up on so many chimneys around here.
We see all three regularly in Montgomery, where the mix of older housing near the river and mid-century builds along the Route 31 corridor means a lot of chimneys are now well past the point where a thin mortar wash was ever going to hold.
How to check yours without getting on the roof
Binoculars from the ground will tell you most of it. Look for visible cracks radiating across the top slab, a chunk missing from a corner, a gap where the slab meets the flue tile, or the slab sitting flush with the brick rather than projecting past it. Look at the brick immediately below the crown as well: if the top two or three courses look darker, chalky, flaking or streaked white while the brick lower down looks fine, water is coming in from above.
For the cap, check that there is one. A surprising number are simply missing, having rusted through or blown off in a storm without anyone noticing. If you can see one, look for rust, a crushed or dented lid, or mesh that is torn or packed with debris.
Inside the house, water damage from a failed crown shows up as damp or staining on the firebox walls, a musty smell, rust on the damper, or white deposits on the interior brick.
Small crown cracks can often be sealed with a flexible crown coating rather than rebuilt, which is the cheaper and entirely legitimate answer when the slab is structurally sound. When it has broken up, a rebuild, quoted after inspection, is the real fix, and doing it before the top courses of brick need tuckpointing, which starts at $399, is the difference between one job and two. Caps are covered on our caps and dampers page, broader masonry work on the repair page, and every published number is on pricing.
Have the top of your chimney looked at
Ember Chimney Sweepers is two brothers from Oswego with 35 years of combined experience, insured and bonded, taking calls seven days a week from 7am to 9pm. A crown inspection is part of every Level 1 we do, starting at $99, and finding a cracked crown in October is a considerably better outcome than finding a wet firebox in March.
Written by Josh Amber, co-owner of Ember Chimney Sweepers, Oswego IL. Published October 9, 2026.