When it comes to their chimney, many homeowners wrongly assume it is a singular structure. However, chimneys are actually complex structures with a number of different parts that all work together to keep your fireplace system functioning. One of the often forgotten chimney components is the chimney crown; even though you may not pay it much attention, the chimney crown has an important function.
The chimney crown is the masonry or concrete slab that covers and seals the top of the chimney. The top of the flue extends through the top of the chimney crown, which is then covered by the chimney cap. Chimney crowns play an important part in protecting the chimney system against water damage by keeping moisture from ice, rain, sleet, or snow out of the chimney.
Well-constructed chimney crowns should be made of concrete as this is the most resistant to moisture. Likewise, chimney crowns should be slightly sloped or domed to prevent moisture from building up on top of it around the top of the flue. Lastly, chimney crowns often have a lip of two to two and a half inches; this edge, known as a kerf, prevents water from flowing from the chimney cap directly onto the sides of the chimney structure. Instead, it drains harmlessly onto the roof.
What causes chimney crowns to deteriorate?
Even if the rest of the chimney structure is sound, the chimney cap may be damaged or need to be repaired. This happens because chimney crowns often bear the brunt of the elements. Because they are flat or slightly sloped, snow and moisture are able to accumulate on the chimney crown; the masonry of the chimney itself is often saved from this kind of deterioration because of its straight vertical sides.
Another major issue that can occur with chimney crowns is deterioration due to the building material. Chimney crowns should never be mortar based or constructed using brick. Both of these building materials are too porous to be able to effectively keep water out of the chimney. Chimney crowns should be made of concrete – or in some cases metal – as it is best able to withstand moisture without being damaged.
Chimney crowns can also be damaged by exposure to changes in temperature. During the winter, for example, the flue itself may be extremely hot even when the masonry of the chimney is cold. This temperature difference can cause the chimney crown to expand and contract, losing the seal around the flue and potentially letting moisture into the chimney.
Why is a chimney crown important?
A well maintained chimney crown is an important part of keeping your entire chimney system in good condition. Without it, moisture can enter the chimney structure, putting everything from the flue to the firebox at risk for water damage. Chimney crowns are checked for signs of damage or deterioration during your annual chimney inspection; to schedule your chimney inspection, contact Mountain Man Fireplace & Chimney today!