ABAG Shaken Awake! Report -
Wood-Frame Multifamily Buildings

1-3 Stories, Built After 1939

Typical Building Damage

As the Northridge Meadows Apartments have shown, this design formula can offer little resistance to the lateral seismic forces. The performance of the parking structure in past earthquakes has not been good. Three story buildings with a "soft" first story are vulnerable to lateral forces as there typically is inadequate lateral bracing at the ground level in a non-moment-resisting frame.

Typical Damage to Three Story Apartment Building

Source -- Jeanne Perkins -- Superior Apartments, Northridge, 1994


Since these buildings were built at a time when significant parking requirements were in place, it is extremely common for these buildings to have either most or all the first level dedicated to parking. The typical design formula has been that of two levels of living space over either on grade, half a level below grade, or below grade parking. In each case, the living area is usually supported only by posts, typically steel tubes, with a 4x girder connecting them. Also common in this category are three story buildings where the parking level is constructed out of concrete masonry unit (CMU) bearing walls.

Occurrence of This Building Type in the San Francisco Bay Area

Three-story multi-family buildings with the first level dedicated to parking are a fairly new phenomena. In some of the more recently urbanized areas of the Bay Area, as in most of Santa Clara and Contra Costa counties, there is a high percentage of these types of buildings. In Santa Clara County for example, they account for 27% of the total housing stock. Often they are only 20 or 25 year old buildings and have not been exposed to significant seismic forces yet. Over the entire Bay Area, units in this type of building represent 21.3% of the total housing stock. Their numbers are particularly significant in some of the more recently urbanized counties; in Contra Costa and Santa Clara counties, for example, they represent 88.5% and 87.1% of the multi-family 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.