The chimney crown is the concrete (sometimes stone) layer that covers the top of a masonry chimney. It’s one of those classic “out of sight, out of mind” components of your house, since it’s way up high and usually hard to see even if you’re trying to. But it’s exposed to the elements continuously, so if your chimney is old then there’s a good chance that the crown is deteriorated. And that means there’s a good chance there’s a problem with the masonry chimney also.
The job of the crown is to keep water out of and away from the chimney, and water is your home’s number one enemy. Deterioration of the crown and the chimney is certainly a slow process, but if your chimney is old then it’s had a long time to deteriorate. And even if the chimney’s newer, neglecting a problem because it won’t create havoc until years from now is a rough way to treat your house. It also signals to a potential buyer that you’re not on top of things.
Repairing chimneys can be very expensive, largely because to do work up high requires a lot of set-up time and equipment. So keeping the crown in good condition (and installing it right in the first place) will contribute to the long-term health of your house and reduced maintenance costs down the road.
A good chimney crown should be nice and thick to help prevent it from cracking. Anything built of concrete can crack of course, but the thicker something is the lower the stresses are likely to be and so the lower the chance of cracks. And if a crack does develop it’s less likely to go all the way through a thick material, and it’s easier to seal the crack.
This chimney crown is great. It’s well designed and in good condition, with rain caps on top of both flues.
This chimney cap is well designed, but it’s cracked. And the masonry below the crack is starting to show signs of damage. This crack should be sealed.
The crown should be pitched towards the edge to help shed water.
The crown should overhang the masonry of the chimney to help shed water away from the masonry. If the edge of the crown lines up with the bricks then as water drains off it will just run down the chimney. Much of that water will actually soak into the bricks, and that will cause deterioration.
This crown is thick (but there’s still a small crack and no rain cap), but it doesn’t overhang the bricks. Water runs off the crown and directly onto the bricks. The mortar joints around the top are pretty badly deteriorated because of this.
There also should be a rain cap on top of every flue. Allowing water to run down the flue every time it rains will lead to much quicker deterioration. There’s no reason to have that happen. A rain cap can also reduce downdrafts that can lead to dangerous backdrafting, and it can help keep animals out of the flue.
This chimney doesn’t even have a crown. It’s had a lot of work done to it recently, and it’s going to need a lot more in just a few years. This is awful.
It can be easy to ignore a chimney crown like this. It’s certainly out of sight. But this is in terrible condition, and eventually the bill will come due.