How Does LA's Soft-Story Retrofit Program Work?

The city's ordinance targets the building type that failed in Northridge: wood-frame construction of two or more stories, built before modern seismic detailing, with a ground floor that is mostly open for parking or retail while the floors above are full of apartments. Engineers call the open level a soft story when its lateral stiffness is far lower than the story above, and a weak story when its strength is far lower; most dingbats are both. The evaluation confirms which irregularities are present and how severe they are, because the retrofit scope follows the measured deficiency, not a one-size-fits-all detail. Non-ductile concrete buildings fall under a separate track of the same ordinance, with their own evaluation criteria and compliance framework. Buildings outside the city limits are not subject to the city ordinance at all: unincorporated county sites permit through Los Angeles County, and each neighboring city with its own ordinance sets its own covered building types, deadlines, and submittal requirements. The engineer verifies the AHJ and the applicable program rules at the start of the project, because designing to the wrong jurisdiction's standards is one of the most expensive mistakes in retrofit work.

The standard retrofit threads new steel into the open ground floor with minimal loss of parking. Steel special moment frames span the open bays where carports need clear widths, while cantilevered steel columns work where a full frame will not fit. The engineer sizes each frame for the seismic forces the code assigns to the building, checks the existing upper diaphragm for its ability to deliver those forces, and adds plywood overlays, blocking, and collectors where the old floor framing falls short. New footings go under every new column, designed for both gravity and the overturning the frames produce. Connections make or break the retrofit. Holdowns and anchor bolts tie the steel frames to the wood sill and rim above; the steel itself is detailed for ductile yielding so it bends rather than fractures; and welds and high-strength bolts get special inspection during construction. The engineer also coordinates with the architect and tenants, because new steel columns in a carport change clearances and the work happens in an occupied building. Structural observation during construction closes the loop, confirming the built work matches the permitted drawings.