The California earthquake building code is not a single document but a layered framework: Title 24 of the California Code of Regulations sets structural design standards statewide, the Alquist-Priolo Act and the Seismic Hazards Mapping Act control where buildings can go, and separate state and local laws force older buildings to be strengthened. Together these rules determine how every structure in California gets sited, designed, built, sold, and maintained.
What the Code Requires for New Construction
The California Building Code is published as Title 24, Part 2 of the California Code of Regulations and updates on a three-year cycle. It requires engineers to design buildings with lateral force-resisting systems sized to the seismic loads at the specific site, based on location, occupancy type, and soil conditions.
Every structure is assigned a seismic design category from A (lowest risk) through F (highest). Categories D, E, and F carry stricter rules on which structural systems can be used, tighter connection detailing, and mandatory special inspections during construction. Common systems used to meet these requirements include reinforced concrete shear walls, steel braced frames, and wood-frame shear walls with specified nailing patterns and hold-down connections.
The 2025 Code, Effective January 2026
The 2025 edition of Title 24 was published July 1, 2025 and takes effect January 1, 2026. All new permit applications filed on or after that date must comply with it.1California Department of General Services. 2025 Title 24 California Code Changes
The biggest change for structural work is the adoption of ASCE 7-22, which replaces ASCE 7-16 as the governing standard for seismic, wind, and other environmental loads. ASCE 7-22 uses multi-period response spectra instead of the older two-coefficient method, brings revised seismic hazard maps, and updates site coefficients and base-shear calculations. Design loads have shifted in several California regions, which can change steel tonnage, shear-wall requirements, and foundation sizing even on projects that look similar to ones permitted under the prior code. The 2025 edition also repeals several California-specific amendments that ASCE 7-22 now addresses directly, including provisions on two-stage analysis procedures and extreme torsional irregularities.2California Department of General Services. 2025 Part 2 Chapters 16 and 16A Structural Design
Where You Can Build: Fault Zones and Hazard Maps
Two separate state laws restrict where construction can happen before the building code even comes into play.
The Alquist-Priolo Earthquake Fault Zoning Act prohibits placing structures intended for human occupancy over the surface trace of an active fault. A building generally must sit at least 50 feet from any fault that has ruptured in the last 11,000 years.3California Department of Conservation. Alquist-Priolo Earthquake Fault Zones The state continues to update its fault zone maps as new data emerges.4Justia. California Public Resources Code 2621-2630 – Earthquake Fault Zoning
The Seismic Hazards Mapping Act of 1990 requires cities and counties to obtain a site-specific geotechnical report before approving projects in mapped hazard zones. The report must identify risks such as liquefaction and landslides and recommend specific measures to reduce them to acceptable levels. A local agency can waive the report only if nearby studies on similar soil already show no undue hazard.5Justia. California Public Resources Code 2690-2699.6 – Seismic Hazards Mapping
Older Buildings: Mandatory Retrofit Rules
Two categories of existing buildings carry legal obligations beyond the ordinary code.
Unreinforced Masonry Buildings
California’s Unreinforced Masonry Building Law, Government Code Section 8875 and following, required local governments in the highest seismic zones to inventory their unreinforced masonry buildings and establish earthquake risk-reduction programs. Those programs recommend mandatory strengthening ordinances, retrofit standards, and measures to reduce occupancy in the most vulnerable structures.6California Seismic Safety Commission. Status of the Unreinforced Masonry Building Law
Soft-Story Buildings
Soft-story buildings are typically wood-frame apartment buildings with open parking or commercial space on the ground floor, creating a weak level that can collapse in a quake. Several California cities have passed mandatory retrofit ordinances aimed at them. Los Angeles requires owners of wood-frame buildings with four or more units built before 1978 and a vulnerable ground floor to submit retrofit plans within two years of a compliance order, obtain permits within three and a half years, and finish all work within seven years. Santa Monica, West Hollywood, and Pasadena have adopted similar programs.
The state law itself does not mandate retrofits on ordinary single-family homes. Retrofit obligations for houses come from voluntary programs and from the reality that a home built to older codes may not meet current insurance, financing, or resale expectations.
What Sellers Must Disclose
California ties earthquake safety directly to real estate transactions. When selling a home, the seller must give the buyer a Natural Hazard Disclosure Statement indicating whether the property sits within an earthquake fault zone or a seismic hazard zone, including liquefaction and landslide zones. If the available maps are not detailed enough to make a definitive call, the default answer is “Yes.”
Sellers of older homes carry extra duties. For residential properties built before 1960 with one to four units of conventional light-frame construction, the seller must deliver a copy of the “Homeowner’s Guide to Earthquake Safety” to the buyer as soon as practicable before transfer, and must disclose any known earthquake deficiencies in the property. The law does not require the seller to hire an inspector, open walls to investigate hidden conditions, or repair any earthquake-related deficiencies before the sale.7California Legislative Information. California Government Code 8897.1 Sellers must also properly strap the water heater so it does not topple and break gas or water lines during a quake.
Grants and Insurance Discounts for Retrofitting
Retrofitting an older house typically costs between $3,000 and $9,000 for standard foundation bolting and cripple-wall bracing, depending on size, foundation type, and local labor rates. Two state programs help defray that cost.
The California Residential Mitigation Program runs Earthquake Brace + Bolt (EBB), which offers grants of up to $3,000 to qualified homeowners who bolt their house to its foundation and brace crawl-space walls. Income-eligible households earning $89,040 or less per year may qualify for up to $7,000 in supplemental grants, which can cover most or all of the retrofit cost.8California Earthquake Authority. Earthquake Brace + Bolt Grant Program Opens Again for 2025 Eligible homes must have been built before 1980, sit on a raised foundation rather than a slab, and be located in a qualifying ZIP code.9California Department of Insurance. Earthquake Brace and Bolt Grant Program Opens for 2025 Applications
The California Earthquake Authority offers premium discounts of up to 25% on earthquake insurance for retrofitted homes. To qualify, the home must be a wood-framed single-family dwelling with one to four units, built before 1980, on a raised or other non-slab foundation, with the water heater properly secured to the building frame. The discount depends on age and foundation type:10California Earthquake Authority. Earthquake Insurance Policy Premium Discounts
- Built 1940 through 1979: 20% for raised foundations, 10% for other non-slab foundations.
- Built 1939 or earlier: 25% for raised foundations, 15% for other non-slab foundations.
How the Code Got Here
Every major California earthquake exposed a weakness in existing construction, and the legislature responded by tightening the rules.
The 1933 Long Beach earthquake destroyed 70 schools and damaged hundreds more. Within days, Assemblyman Don C. Field drafted a bill charging the Division of the State Architect with overseeing school construction, and Governor James Rolph signed it a month later. The Field Act required structural plans prepared by licensed structural engineers and approved by an independent state agency, and it still governs California school construction today.11ShakeOut. The Field Act and Public School Construction: A 2007 Perspective
The 1971 San Fernando earthquake, magnitude 6.6, caused surface fault ruptures that tore through buildings sitting directly on faults. The Alquist-Priolo Act followed.3California Department of Conservation. Alquist-Priolo Earthquake Fault Zones
The 1989 Loma Prieta earthquake showed that structures on soft soil shook far more violently than those on bedrock. The U.S. Geological Survey documented the finding, and it drove significant changes in national seismic provisions.12United States Geological Survey. Progress Toward a Safer Future Since the 1989 Loma Prieta Earthquake California followed with the Seismic Hazards Mapping Act in 1990.
The 1994 Northridge earthquake fractured welded steel moment-frame connections that engineers had considered among the safest available. FEMA published guidance covering new construction, retrofit of existing buildings, and repair of damaged structures, and model code organizations rewrote their steel-frame provisions.13FEMA. Building Code Lessons From the 1994 Northridge Earthquake Those reforms were folded into the 1997 Uniform Building Code, which became the base for the 1998 and 2001 editions of the California Building Code.14California Department of General Services. History of the California Building Code – Title 24, Part 2
Liability for Ignoring the Rules
Property owners in California have a duty to keep buildings in reasonably safe condition, and in a state where earthquakes are foreseeable, that duty covers seismic preparedness. An owner who ignores a mandatory retrofit order, fails to secure heavy fixtures, or leaves known structural deficiencies unaddressed faces real exposure if someone is hurt in a quake. When a building was properly built, maintained, and code-compliant, and the damage came purely from the earthquake’s force, liability claims against the owner rarely succeed. The legal risk lands on owners who knew about a problem and did nothing.
Noncompliance can also trigger enforcement from local building departments, including notices of violation that become part of the property’s public record. Buildings flagged as noncompliant with mandatory retrofit ordinances may be labeled unsecured for seismic activity, which can complicate insurance coverage, financing, and future sales. For owners of soft-story or unreinforced masonry buildings in cities with active enforcement programs, the practical question is not whether to retrofit but how quickly the work can be finished.