A soft-story building is one of the most common, and most dangerous, structural weaknesses in California's older housing stock. If you own an apartment building with parking tucked under the living units, there is a good chance you own one.
What makes a story "soft"?
A soft story, sometimes called a weak or open-front story, is a floor that has significantly less strength and stiffness than the floors above it. It usually happens on the ground floor, where large openings for parking, tuck-under garages, or storefronts leave too few solid walls to brace the building. The upper floors sit on top of what is essentially a set of tall, slender columns.
Why soft-story buildings fail first
When the ground shakes, a building needs continuous, stiff wall lines to transfer the sideways forces down to the foundation. A soft story cannot. The weak ground floor sways, the columns bend, and the heavy upper floors can pancake down onto the open level below. This is exactly the failure pattern seen in the 1994 Northridge earthquake, where soft-story apartment buildings collapsed and caused loss of life.
How do I know if I own one?
Typical signs are a wood-frame building of two or more stories, built before the late 1970s, with ground-floor parking, tuck-under garages, or large open wall lines on the first floor. Most California cities with mandatory programs also mail owners an order to comply. A free property survey from Cal Retrofit will confirm it either way.
What a retrofit does
A soft-story retrofit adds strength and stiffness back to the weak floor. Depending on the engineering, that means steel moment frames at the open-front bays, cantilever columns where frames will not fit, and shear-wall reinforcement, hold-downs, and structural anchoring tied into the foundation. The result is a building that stays standing when the ground moves. You can see what a retrofit typically costs and the ranges involved.
Is it required where I am?
In much of Southern California, yes. See your city for the specific ordinance and deadline: Los Angeles, Santa Monica, Beverly Hills, West Hollywood, Culver City, Pasadena, or Burbank.