Mobile Home Earthquake Bracing: What California Requires

An earthquake resistant bracing system, or ERBS, is a set of supports added under a mobile home to limit how far it can drop if it shakes off its piers. In California it is optional. If you add one, it must be a certified, labelled system designed to limit a drop to 2 inches, installed under its own permit by the registered owner or a CSLB-licensed contractor, and inspected. This page sets out those rules. We do not recommend any product by name. Ask about the system’s certification and label on any quote.

Why owners here ask about it

USGS puts the chance of a magnitude 6.7 or larger earthquake somewhere in Southern California within 30 years at 93%, and USGS notes that the southeastern end of the San Andreas, the stretch that runs along the Coachella Valley, has not ruptured since about 1680. In the USGS ShakeOut scenario for a large southern San Andreas earthquake, the Coachella Valley gets strong shaking of long duration and I-10 in the valley is offset by up to 6.7 meters. In that same scenario, mobile homes had the highest rate of extensive or complete damage of any building class.

That is a scenario, not a forecast. Nobody can tell you when or whether it will happen. But it explains why some owners want to know what their options are.

What the rules say

• It is optional. Title 25 says nothing in the bracing rules requires an ERBS to be installed.
• It must be certified and labelled. The system has to be designed to limit downward movement of the home to a maximum of 2 inches, and it bears a permanent label.
• It needs its own permit. A permit comes from the enforcement agency before an ERBS is installed, replaced or altered, separate from any permit for leveling or tie-downs.
• Who may install it. The home’s registered owner, or a contractor licensed by CSLB. Ask for the licence number and check it on CSLB’s Check a License page.
• The park signs off on digging. The installer has to get the park operator’s written approval before excavating for footings.
• It is inspected. The enforcement agency inspects each bracing installation.

Tie-downs are a different thing

Riverside County’s guidance says wind tiedowns generally do not qualify as earthquake bracing. Straps and anchors resist wind; a bracing system is built to catch the home if it comes off its supports. A home can have good tie-downs and no bracing at all.

Where we fit in

If the home is also out of level or has failed piers, that is separate work. We can relevel the home, rebuild the piers, and check the ground and access, and give you a written quote for that part. If you decide on bracing, ask anyone who quotes it for the system’s certification label, the permit, the park’s written approval and the contractor’s CSLB licence number. Our California rules page explains the permit side in more detail.

A note on paperwork

Owners are sometimes told that a form 433A covers earthquake bracing. It does not. HCD 433A is recorded only when a home becomes real property on a permanent foundation, and a pier-set park home gets an Installation Acceptance instead. Bracing is its own permit.