Why the ground storey gives way
A soft storey is a floor with far less wall in it than the floor above. The state's earthquake safety guide for commercial property puts it in plain terms: older wood-framed buildings, apartments in particular, are described as having a soft or weak storey problem when the ground-level floor has either carport-style parking or commercial space with large windows and few solid walls. The units above are rigid; the storey under them is not.
The condition is a shape, and the code turns it into a number. Tuck-under parking gives every unit a space without taking land, and a wide shopfront sells; both leave one or two wall lines at ground level doing a full storey's work. The 2025 California Existing Building Code, Appendix A Chapter A4, draws the line at A402.1: a wall line may be taken as soft where the storey's stiffness is less than 70 percent of the storey above it, and weak where its strength is less than 80 percent. The evaluation puts the building on one side of those numbers or the other.
The work is voluntary in this region, and the reason to do it is not a deadline. The state's unreinforced masonry programme reaches only jurisdictions inside the 1985 Seismic Zone 4, under Government Code 8875.1, and it was written for brick rather than for apartments. The Seismic Safety Commission's 2006 report on that law recommended standards and programmes for other collapse-risk buildings, naming soft-story apartments among them; that was a recommendation, and it did not become law.
The same buildings usually carry the other structural obligation on this site. A three-storey walk-up with an open ground storey almost always has balconies and walkways above it, and those are on a statutory inspection cycle. Boards and owners already budgeting for a balcony inspection often look at the ground storey in the same year.
What soft story retrofit includes
The ground storey is measured against the storey above it: how much wall there is on each line, where the openings are, and what is carrying the floor over the parking or the shopfront. The evaluation names the lines that need work and produces the drawings.
The drawings go to the building department for the jurisdiction with the permit application, prepared under the California Building Standards Code, so the route chosen is on the face of them.
Parking spaces, storage and the ground-level route in and out are affected line by line, so residents and ground-floor tenants are told what closes before it does.
Where a wall line is opened under a loaded floor, shoring carries it while the new element goes in, and the layout for that shoring stays on site while it stands.
New shear walls, moment frames or braced frames go into the open lines, with hold-downs and foundation work where the drawings show them.
The building inspector signs the work off, parking and storage go back into use, and the drawings and permit final go into the building's file.
Adding wall where it is easy does not fix a soft storey. The new element goes on the line that is short, tied to a foundation that takes the uplift, or the storey above finds the next weak line.
Where soft storeys are found
Tuck-under parking apartments
Three-storey walk-ups where the ground level is open carport bays, leaving two or three short wall lines to carry everything above them.
Mixed-use blocks
Shops or offices at street level under apartments, where the shopfront glazing takes out most of the wall on the street elevation.
Garden condominium projects
Association-owned buildings with open parking underneath, where the board is usually looking at the ground storey and the balconies in the same budget.
Older motels and courts
Wood-frame units over open bays and breezeways, where the ground level was built as circulation rather than as structure, and the wall lines run one way only.
Corner buildings
Two open elevations meeting at the corner, so the storey is short of wall on both street sides and twists as well as racks.
Buildings with added floors
Where a storey was added later over a ground level designed for what was there before, and the wall below was never revisited.
Questions about soft story retrofit
By what the ground level is made of. If it is carport bays, breezeways or shopfront glass under wood-frame units, the condition is likely. The state's guide describes it that way rather than as a measurement an owner can take; the evaluation then tests it against the code's thresholds - stiffness under 70 percent, or strength under 80 percent, of the storey above - and sizes the work.
Usually not. The work sits at ground level, in the parking bays or behind the shopfront, and it is run one wall line at a time. What goes is the use of that line while it is open: parking spaces, a storage room, sometimes a section of the frontage.
Yes. New shear walls and frames are structural work and go through the building department for the jurisdiction on the drawings prepared for them. Which department that is, and how it takes an application, is on the city page for the property.
Partly. Bays on the line being worked are closed while the wall or frame and its foundation go in, and they come back when the inspector has signed that section off. The sequence is set at the site visit, not afterwards.
Where a city's own file records a retrofit ordinance, that city's page says so and the work follows it. Otherwise the position is the state one, and a soft story retrofit is something an owner chooses.
Soft story retrofit by city
Soft story work is requested through the structural repair page for your city, which covers the stock and the permit route there.
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