The chimney crown, which can also be referred to as a chimney wash, is a large slab that covers the top opening of the chimney. Unlike a chimney cap, which is typically made of metal and merely covers the opening to the flue, the chimney crown covers the entire top of the chimney. Chimney crowns may be made of metal, concrete, or stone. However, they should never be constructed using bricks and mortar, as these materials are not water proof and will deteriorate quickly when exposed to the elements.
Why are they important?
The main and most important purpose of a chimney crown is to protect the chimney structure from deterioration due to weather exposure. Properly installed chimney crowns are able to achieve this by extending over the walls of the chimney structure. This overhang, called a kerf, should extend 2-2.5 inches over the chimney structure. Doing this creates a form of a rain gutter, allowing rain, snow, and other moisture to move away from finding its way onto the chimney. Instead, kerfs direct the water onto the roof where it can then harmlessly drain without damaging the bricks and mortar of the chimney structure.
What to do if my chimney crown is damaged?
Chimney crown damage can often be difficult to spot because it is impossible to see from the ground. Instead, chimney crown damage can only be seen when inspecting the chimney from the roof. Because of this, most chimney crown damage is only found during chimney sweepings or inspections.
If the mason who built your chimney also constructed your chimney crown, it may be made of mortar. While mortar is the perfect material to bind bricks together, it should not be used for chimney crowns as it deteriorates quickly when exposed directly to the elements. Likewise, ill maintained chimney crowns can develop cracks or holes which can allow water to enter the flue and firebox.
Because chimney crowns are specifically fitted to each individual chimney, they should be custom built by a reputable chimney repair company. Having a chimney crown professionally built and fitted can extend the life of the chimney crown for decades.