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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 are 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 about 1960, building codes in some states have required that all chimneys be reinforced and strapped to the structure. However, in several recent California earthquakes, rods connecting the chimney to the roof caused the chimney to fall through the ceiling as a unit which was far more damaging than if the chimney had merely cracked and fallen in pieces.
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.
Hire a contractor or structural engineer to check your chimney.
Reinforce the ceiling surrounding the chimney with 3/4 inch plywood nailed to ceiling joists.
Be sure to have the chimney checked, and repaired, if needed, before using it after an earthquake.
A structural engineer will be able to tell you if you need to do additional structural work to protect your house(blocking between joists, additional hold-downs on corners of the house, etc.).
Adapted from FEMA: Mitigations for Homeowners Independent Study Course Unit 4 and EQE International (used with permission)
