Hips and Shoulders: Chimney Corbeling
Chimney Corbeling can cause bigger problems so it is best to get the issue fixed sooner rather than later. The corbeling hips on your chimney could be allowing damaging water to come into your home. Corbeling aligns the shape of the smoke chamber to allow for better air flow inside the chimney. By design, the smoke chamber height can not be any bigger than inside width of the fireplace room opening, and the depth should not be greater than the depth of the smoke chamber. The smoke chamber has to be placed at 45-degree angle and perched smooth on the inside.
The shape of the smoke chamber should be capped off so not water can penetrate. Do it with concrete stones as you can see below. It is most important during construction any open voids of the brick itself are properly filled to prevent water penetration. Always remember small holes can allow gallons of damaging water in the chimney smoke chamber and even down into the firebox below. In the 60s 70s and 80s, many builders cut costs by making these flat instead of pitched at all. We’d always recommend having your chimney contractor take a picture of the top of the corbeling to determine if it needs a new stone cover, silicone waterproofing, or grind it out and tuck point it.