The Wrong Type of Chimney Cap Can Cause Problems

Cement Cap with Crack and Separation

The cement cap on top of masonry chimneys is the single most problematic area of any chimney.  As chimney service technicians, we know that the cement cap (or crown) is often cracked, deteriorated, and separated from the top course of brick, leaving areas where rainwater can seep in and enter the chimney chase.

Cracks often develop because most masons do not install a bond break around flue liners as is required by code, and when flue liners are heated they expand and push on the cement cap. Cracks may also develop during a sudden chimney fire or lightning strike.

Deteriorating Cement Cap

Cement caps are susceptible to weather damage and will deteriorate over time. This area is the most difficult to see because it cannot be viewed from the ground.

Poor Chimney Design

Right: This is a poor design for a chimney. Rainwater runs off the cement cap and directly on to rows of bricks. This upper portion of the chimney will deteriorate much more quickly than the rest of the structure.

Left: There is nothing left of the cement cap that used to be on the top of this chimney. Rainwater has been pouring into the interior of the chase for years, causing deterioration of the mortar joints inside the chase.

This type of damage can be very costly. Both the interior and exterior chimney need repair.




Right: This mortar joint between two tile flue liner sections has been completely washed out due to exposure to rain water on both the outside  and the inside of the tile. Gaps like this can allow toxic and heated flue gasses to escape the chimney.

Cement cap with drip edge. Note: the chimney
is too short and should have been raised.

The 2012 International Residential Code requires a cement cap to have a drip edge and a slope to permit water runoff away from the top courses of bricks on the chimney. Without this drip edge water runs onto the upper bricks and mortar, causing excessive deterioration.
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Marge Padgitt is the CEO and President of HearthMasters, Inc. and HearthMasters Masonry School in Independence, MO. Contact her at www.chimkc.com.