ABAG Shaken Awake! Report -
Mobile Homes

Typical Mobile Home Damage

Mobile home units statistically tend to be subject to greater damage from equivalent intensities of shaking than do wood-frame dwellings. In an earthquake, the typical jacks on which the coach is placed will tip, and the coach will fall off some or all of its supports. It is not uncommon for the jacks to punch holes through the floors of the coach in this process. The mobile home unit usually remains relatively undamaged. The major problem is that even at these relatively low damage amounts, the mobile home becomes uninhabitable; it must be returned to a foundation, re-leveled and reconnected to utilities.

Typical Mobile Home Damage Photo

Source -- Courtesy of Karl Steinbrugge

Mobile Home Construction

A mobile home is a factory-built dwelling built entirely of light-weight metal construction or a combination of a wood and steel frame structure. When combining wood and steel, the wood frame structure is erected on a steel frame chassis. In either case, the exterior is typically protected with siding of wood, aluminum or fiberglass. Mobile homes are often structurally linked to a second unit forming a double-wide coach. The units can be pulled on wheels to a site, leveled, and supported in one of the following ways.

  1. The coach can rest on the ground with only small metal devices called screwjack levels between it and the soil. The screwjack level consists of a metal triangle shaped base, similar to a tripod, with a screw and plate to connect it to the coach.
  2. The coach can be supported above ground by resting on piers which are generally spaced about six feet apart. The undercarriage is leveled between these piers with screwjack levelers or wood blocks (called shims). The piers are made of concrete, steel, unreinforced concrete, or cinderblock. These piers can rest on either a concrete slab or on treated wood that sits directly on the ground.
  3. The coach can be supported by reinforced concrete foundation units at the corners coupled with tie down connections to it
The mobile home unit should be attached to natural gas lines with flexible connections. Engineered tie-down systems and earthquake resistant bracing sytems can improve performance. Placement of the unit on a permanent concrete perimeter foundation is preferred.

Mobile Homes in the San Francisco Bay Area

Mobile homes comprise only 2.8% of the total Bay Area housing stock. Their presence varies significantly by county. The county with the most mobile homes is Santa Clara, with 30.7% of the mobile homes in the region. However, within this county they comprise only 3.8% of the total housing stock. On the other hand, the counties of Napa and Sonoma have the highest percentage of mobile homes: 8.8% and 7.3% respectively.

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 9/26/03 by jbp.