Many older Los Angeles houses were built before modern seismic rules. In a strong earthquake, a wood frame house that is not attached to its foundation can slide off it, and short crawl space walls can collapse. A seismic retrofit addresses both problems, and it is one of the most cost effective safety upgrades an older home can get.
Is your home a candidate?
Your house may benefit from a retrofit if most of these are true:
- It was built before about 1980
- It has a raised foundation with a crawl space
- It has short wood walls, called cripple walls, between the foundation and the first floor
- You do not see anchor bolts or steel plates connecting the wood sill to the concrete
Part 1: Bolting the house to the foundation
The wood board that sits on top of the foundation is called the sill plate. A retrofit adds anchor bolts or steel foundation plates that tie the sill plate to the concrete at regular spacing. This keeps the house from sliding off the foundation when the ground moves.
Part 2: Bracing the cripple walls
Cripple walls are often framed with studs and siding only. In an earthquake they can fold over like a row of dominoes. Bracing them with structural plywood panels, nailed on a specific pattern, turns them into shear walls that resist that sideways force.
What a retrofit does not do
Bolting and bracing will not fix a cracked or deteriorated foundation. If the concrete is weak, unreinforced, or badly cracked, the foundation itself may need repair or replacement first. A proper inspection will tell you which situation you are in.
Check for state grant programs
California's Earthquake Brace + Bolt program has offered grants toward retrofits for qualifying homes in selected ZIP codes. Availability and eligibility change, so check earthquakebracebolt.com for current rounds before you start.
Single family homes vs. apartment buildings
Los Angeles has a mandatory retrofit ordinance for certain older wood frame apartment buildings with weak ground floors, often called soft story buildings. Retrofitting a single family home is generally voluntary, but it can add peace of mind and may be worth discussing with your insurer.
How the work goes
Most retrofits are done entirely from the crawl space, so you can stay home during the work. The job typically includes an inspection, a permit, installation of bolts and bracing, and a city inspection. Because crews are already under the house, it is also a good time to check posts, piers, plumbing, and drainage.
Common questions
How long does a seismic retrofit take?
A typical bolt and brace retrofit on a single family home takes a few days once permits are in hand. Homes that also need foundation repair will take longer.
Does a retrofit lower earthquake insurance premiums?
Some earthquake insurance providers offer discounts for retrofitted homes. Ask your insurer what documentation they need.
My house is on a slab. Do I need this?
Bolting and cripple wall bracing are designed for raised foundation homes with crawl spaces. Slab homes have different considerations, which an inspection can identify.
This guide is general information for homeowners. Every house is different, so an on site evaluation is the only way to know what your home needs.