ABAG Shaken Awake! Report -
Wood-Frame Single-Family Homes

1-3 Stories, Built Before 1940

Typical Building Damage

Typical earthquake damage to these structures includes the wood frame coming off its foundation, racking of the cripple walls, the foundation itself cracking, or the chimney breaking at the roof line. Because this type of damage is so common, earthquake hazard mitigation efforts in some Bay Area building departments are directed toward them.

Typical Damage to Pre-1940 Single-Family Home

Source -- Jeanne Perkins -- Loma Prieta Earthquake, 1989


A typical problem with houses built during this era is the connection between the wood frame and the foundation. These houses often lack steel bolts or any other type of "tie-down" between the foundation and the wood frame. Since these houses were built before the widespread use of plywood, they also typically lack appropriate shear reinforcing of the cripple walls (the walls between the top of the foundation and the floor diaphragm). Finally, steel reinforcing often is not found both in the foundation of these houses as well as in their chimneys. Some of these older houses may be only founded on brick with weakly cemented joints.

Occurrence of This Building Type in the San Francisco Bay Area

Pre-1940 single-family dwellings account for 8.3% of the total Bay Area housing stock. Their relative numbers are highest in the counties of San Francisco and Alameda where they account for 14.9% and 11.7% of the total housing stock.

ABAG, the Association of Bay Area Governments, is the regional planning and services agency for the nine-county San Francisco Bay Area.

This page is based on a 1996 ABAG report. It was last updated 9/29/03 by jbp.