Inspecting Chimneys Series

The Old House Web

Editor's note: This story is adapted from the U.S. Department of Housing and Urban Development's Residential Rehabilitation Inspection Guide, 2000.Click here for other stories in this series.

Parts of this story: Introduction ~~ Seismic and wind resistance ~~Cracking and deterioration of masonry, general issues ~~Masonry foundations & piers~~Above ground masonry walls ~~ Chimneys ~~Wood structural components ~~Iron and steel structural components ~~Concrete structural components


A deteriorated chimney cap. Mortar, rather than concrete, is often improperly used (as it was here) to cap a chimney. The masonry below will eventually deteriorate if the cap is not replaced.

Chimneys, like parapets, have greater exposure to the weather than most building elements, and have no lateral support from the point where they emerge from the roof. Common problems are:

  • Differential settlement of the chimney caused by an inadequate foundation. If the chimney is part of an exterior wall, it will tend to lean away from the wall and crack where it is joined to other masonry. In some cases, the chimney can be tied to the building. Consult a structural engineer.
  • Deterioration of masonry near the top due to a deteriorated cap that allows water into the masonry below and exposes it to freeze-thaw cycles. This cap is often made of a tapered layer of mortar, called a cement wash, that cracks and breaks after several years. Check the cap. If it is mortar and the chimney has a hood, repair the mortar. If it is mortar and the chimney does not have a hood, replace the mortar with a stone or concrete cap. If the cap is stone or concrete, repair it or replace it.
  • Leaning of the chimney where it projects above the roof due to deteriorated mortar joints caused either by wind-induced swaying of the chimney or by sulfate attack from flue gases and particulates within the chimney when the chimney is not protected by a tight flue liner.

Deteriorated mortar joints should be pointed, and unstable chimneys or those with a noticeable lean should be dismantled and rebuilt. Chimney-mounted antennas should be removed if they appear to be causing structural distress.

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