In past earthquakes, masonry chimneys have proved to be one of the most damage-prone and hazardous features of a house. Taller chimneys tend to be more susceptible to damage than shorter chimneys. It is important for your family to understand the hazard that the chimney represents and to stay away from it during an earthquake.

Since around 1960, building codes in California have required that all chimneys be reinforced and strapped to the structure. These two requirements typically reduce the likelihood of serious damage. However, in several recent earthquakes, many such chimneys were severely damaged and required demolition, and some even collapsed. Typically, the collapsed chimneys were poorly constructed or the metal straps were not adequately tied to the house. (These straps are usually visible in the attic and should be nailed or bolted to the ceiling framing or blocking.)

Unreinforced masonry chimneys frequently topple in earthquakes, with the portion projecting above the roof line being the most susceptible to damage. The safest thing to do with an unreinforced masonry chimney is to remove it and replace it with a prefabricated metal flue system with a wood enclosure.

As an intermediate step, the top portion of an unreinforced chimney can be removed and replaced with a metal flue with a wood frame or a reinforced portion that is tied into the roof. The higher the projection above the roof line, the stronger the recommendation for strengthening. If the chimney is located such that its falling would not injure anyone or damage property, adding plywood at the roof or attic level to minimize building damage and protect occupants may be an acceptable alternative.

In any event, the chimney should be inspected for cracks or weak mortar by a qualified contractor as a minimum. Weathering is typically most severe at the top, which is not visible without close inspection.