When homeowners think about the parts of their chimney and fireplace that need to be maintained, they often leave out one crucial element – the chimney crown. Although often ignored, the chimney crown is one of the most important parts of a fireplace system, protecting the inside of your chimney, fireplace, and home from damaging moisture.
What is a chimney crown?
A chimney crown is the concrete, slightly domed slab that covers the top of the chimney. The flue or flues of the chimney extend through the top of the chimney crown and are covered with their own chimney caps. Also known as a chimney wash, their main purpose is to allow moisture from rain, snow, sleet, or ice to flow away from the flue and onto the roof, preventing water from entering the chimney system.
Unfortunately, during construction many chimney crowns are incorrectly installed using improper materials. Some bricklayers improperly create the chimney crowns using a mortar-based mix. Because of this, the constant exposure to moisture and the elements causes the chimney crown to prematurely age and crack.
Why do chimney crowns deteriorate?
Chimney crowns are often the first part of a chimney system to deteriorate or need major repairs for several reasons. First, chimney crowns are virtually flat; snow and rain accumulate on top of them rather than running off as with the sloped or vertical sides of the chimney and roof. Second, they are repeatedly exposed to varying temperatures. While the flue may be hot due to the exhaust from an interior fire, the masonry itself is often cold due to outside temperatures. This disparity in temperature causes expansion and contraction, especially on the seals around the flue, which causes the crown to deteriorate at a faster rate.
Lastly, due to their location chimney crowns are virtually invisible from the ground. Because of this, most homeowners have no idea that their crowns are weakening. Most chimney crown cracks or defects are spotted by chimney sweeps during their annual inspections.
How do I know if my chimney crown is properly built?
While it is best to have your chimney crown evaluated by a professional, there are several key elements to look for when assessing your chimney crown. First, a chimney crown should never be constructed out of bricks and mortar. Instead, look for a crown that is made of concrete, metal, or other solid slabs of stone. These solid pieces will often last longer as there is less potential for water to penetrate the surface and cause problems.
Most importantly, the edges of a chimney crown should never be flush with the sides of the chimney itself. Instead, look for the edges of the crown to extend at least 2-2.5 inches beyond the sides of the chimney. This lip, known as a kerf, act as a kind of rain gutter, preventing water from travelling directly down the sides of the chimney and potentially damaging the bricks and mortar.
Modern chimney crowns can also be treated with special sealants to protect against and prevent moisture damage. Sealing a chimney crown is often a cost effective way to extend the life of an existing crown while still protecting the rest of the fireplace system.