For those who don’t know much about chimneys, the chimney crown is the very top of your chimney, as the name implies. You may think that the way it is designed has more to do with appearance than functionality, but you’d be wrong. In fact, all of the elements of your chimney crown should be carefully planned to reduce the risk of damage to your chimney and fireplace. If well designed and well built, your chimney crown can help extend the workable life of your chimney.
If your chimney crown is damaged, or if it wasn’t designed and installed properly, you may want to invest in having it rebuilt or repaired. Doing so can help reduce the risk of even more expensive repairs throughout your chimney or even your roof.
What Does a Chimney Crown Do?
At the most basic level, a chimney crown is essentially a roof for your chimney. It sits on top, and is meant to reduce or ideally eliminate water and snow from getting into your chimney. Its function is especially critical to chimneys that are built with masonry components. Water can quickly penetrate into the masonry of your chimney—both the stones or bricks and the mortar holding them together. Then, if temperatures drop, that water could freeze. The rapid expansion causes pressure on the mortar bonding the masonry together, which can cause damage or even outright breaking and crumbling of the mortar.
Larger stones and bricks can also be damaged by freezing water, depending on how porous they are. Given the risk of substantial damage and loss of functionality, it’s important that your chimney crown perform its duties properly.
Why Does Your Chimney Crown Need an Overhang?
A well designed and well built chimney crown can protect your chimney from weather damage and keep it in working condition for many years to come. In order to perform this critical function, certain elements should be present when it’s designed and constructed. The most important factor is likely the overhang. The very top of your chimney crown should extend a bit past the masonry of the chimney itself.
Much like with the overhang designed into most roofs, this overhang is created with the flow of water in mind. When rain comes down, the sloped overhang on the crown keeps it off the chimney. There should be a groove that is at least a 1/4 inch wide and at least 3/8 of an inch deep on the underside of the overhang going completely around the overhang.
The overhang for your chimney crown is likely going to bear the brunt of weathering. It is a very exposed part of your home, roof and chimney. As such, it should be made of a more solid and less porous material than standard masonry mortar. Ideally, your chimney crown’s overhang will be constructed of concrete, which typically has small stones in it. It’s also important to note that if your chimney was built with clay flue liners, the crown should not touch those liners because of how hot they get. The heat could cause the overhang to expand and crack. The gap between should be caulked.
What Other Part Is Important to a Chimney Crown?
The other most important consideration to a chimney crown is the installation of flashing. Most people know that there should be flashing where the chimney meets the roof. Did you know you should have flashing where the chimney crown meets the rest of the chimney as well? That flashing should either be a rubberized material or metal. It should wrap around all four sides and extend at a 45-degree angle to ensure any water that gets past the crown stays off your masonry chimney.