The California Building Code’s seismic requirements are the state’s rules for how buildings must be engineered to withstand earthquakes, and the 2025 edition took effect on January 1, 2026. The code assigns every project a Seismic Design Category based on where it sits, what the soil underneath it looks like, and how critical the building is, and that category then drives nearly every structural decision that follows. On top of the rules for new construction, California and its cities require owners of certain older buildings to retrofit them within fixed deadlines.
The Code Framework
The California Building Code (CBC) sits in Title 24, Part 2 of the California Code of Regulations. The 2025 edition was published on July 1, 2025 and became enforceable on January 1, 2026.1California Department of General Services. Codes California starts from the International Building Code and layers state-specific amendments on top to reflect its seismic hazard.
For the actual engineering math, the CBC incorporates ASCE 7-22, the load standard published by the American Society of Civil Engineers. ASCE 7 prescribes how to calculate earthquake forces, how to combine them with wind and gravity loads, and how to verify that both structural and nonstructural components will perform.2ASCE American Society of Civil Engineers. ASCE 7-22 Minimum Design Loads and Associated Criteria for Buildings and Other Structures The state adds its own amendments in specific areas, particularly for hospitals and essential-service buildings.
How a Project Gets Its Seismic Design Category
Before an engineer designs anything, the project must be assigned a Seismic Design Category, or SDC. Categories run from A (lowest risk) through F (highest), and because California’s mapped ground motions are so high, most buildings statewide end up in SDC D, E, or F. Three inputs determine the category.
Location and Ground Motion
The first input is where the building sits. Mapped spectral acceleration values give the expected intensity of shaking at that location.
Soil Conditions
The second input is what the soil does to those ground motions. A geotechnical investigation classifies the site into one of nine Site Classes, from hard rock (A) to soft, failure-prone soil (F). ASCE 7-22 expanded the older six-class system with three intermediate classes — BC, CD, and DE — so engineers get a more precise read on how the ground will behave.3NEHRP. Seismic Design Requirements H-18-8 The geotechnical report is one of the first documents any seismic-territory project needs.
Risk Category
The third input is how important the building is. Risk Categories run I through IV. Category IV covers essential facilities: hospitals with surgical or emergency treatment capability, fire and police stations, emergency shelters, aviation control towers, water storage facilities needed for fire suppression, and buildings holding enough hazardous material to threaten the public if released.3NEHRP. Seismic Design Requirements H-18-8 Category III covers buildings with large gatherings or major economic consequences if they fail. Standard occupied buildings fall into Category II. Minor structures with minimal life risk sit in Category I.
The final SDC comes from combining site-adjusted ground motion with the Risk Category. The most severe category the calculations produce governs the entire design.
What New Buildings Must Include
Once the SDC is set, it drives structural system choices, detailing, and quality assurance during construction. Higher categories demand more robust systems and tighter detailing.
Lateral Force-Resisting Systems
Every building needs a system to transfer horizontal earthquake forces from the roof and floors down through the walls and into the foundation. The CBC and ASCE 7 prescribe which systems are allowed at each SDC. Common options include shear walls (rigid panels that resist racking), braced frames (diagonal steel members that triangulate the structure), and moment frames (beam-column connections designed to flex without breaking). In SDC D and above, these systems must be detailed to survive repeated back-and-forth loading without losing the ability to carry gravity loads. A “special” moment frame has much more demanding steel detailing than an “ordinary” one used in low-seismic areas.4California Department of General Services. 2025 Part 2 Chapters 16 and 16A Structural Design
Foundations follow the same logic. Anchorage between the frame and the foundation must prevent the structure from sliding or overturning during intense shaking. For wood-frame buildings, that means precisely spaced anchor bolts and hold-down hardware. For steel or concrete, the connection detailing gets considerably more complex.
Nonstructural Components
Some of the worst earthquake hazards come from what’s attached to the building rather than the frame itself. Mechanical equipment, electrical panels, piping, ductwork, suspended ceilings, and interior partitions can fall, swing, or rupture. ASCE 7-22 Chapter 13 requires seismic bracing and anchorage for nonstructural components based on the component’s weight, its location in the building, and whether it contains hazardous materials. Heavy rooftop equipment needs engineered anchorage with calculations on the construction documents. The 2025 CBC clarified which components qualify for exemptions, particularly for light-frame wood construction.4California Department of General Services. 2025 Part 2 Chapters 16 and 16A Structural Design
Seismic Gas Shut-Off Valves
Ruptured gas lines are a leading cause of post-earthquake fires. California law requires approved automatic seismic gas shut-off valves on many building types. These devices detect strong shaking and close the gas supply before a broken line can feed a fire. Requirements vary by occupancy and local ordinance, but new construction with fuel gas piping in most commercial and multi-family residential occupancies should expect this as standard. The valves must comply with the applicable ANSI standard and be installed downstream of the gas meter per the manufacturer’s instructions.
Retrofit Obligations for Existing Buildings
Modern code applies to new work, but the bigger safety problem is the older inventory. California and its cities have mandatory retrofit programs targeting the building types that have performed worst in past earthquakes.
Soft-Story Wood-Frame Buildings
Soft-story buildings are the most widespread retrofit target. These are typically multi-unit residential buildings built before January 1, 1978, with two or more stories over an open ground floor. The ground floor is “soft” because large openings for garage doors or storefronts don’t leave enough wall to resist lateral forces, so the upper portion can collapse onto the first floor.5SFGOV. Soft Story San Francisco and Los Angeles both require owners to retrofit these buildings. Los Angeles divides buildings into priority tiers by unit count. Once an owner receives an Order to Comply, plans must be submitted within two years, permits obtained within three and a half years, and construction completed within seven.6LADBS. Soft-Story Retrofit Program San Francisco runs a similar tier-based program with its own deadlines.
Non-Ductile Concrete Buildings
Non-ductile concrete buildings, built before the mid-1970s, lack the steel reinforcement detailing that lets concrete flex and absorb energy. Instead of bending during a quake, they shatter. Los Angeles has a mandatory retrofit ordinance for these structures with a longer runway because the work is complex and expensive. Owners have three years from the Order to Comply to submit an engineering checklist, ten years to submit full structural analysis and retrofit plans (or demolition plans), and twenty-five years to finish construction. The extended timeline reflects that these retrofits can cost millions and often require tenants to relocate.
Unreinforced Masonry Buildings
California’s Unreinforced Masonry (URM) Building Law, at Government Code Section 8875 and following, required 366 local governments in the highest seismic zones to inventory URM buildings and establish loss reduction programs by January 1, 1990.7California Seismic Safety Commission. Unreinforced Masonry Building Law – Biennial Report The law recommended but did not mandate that jurisdictions adopt retrofit ordinances. Los Angeles enacted an aggressive mandatory strengthening program. Others adopted notification-only programs that inform occupants of the risk but leave the retrofit decision to the owner. Tens of thousands of URM buildings have been retrofitted statewide, but the work is far from complete in smaller jurisdictions that chose weaker program types.
Hospitals
Hospitals sit under the Alfred E. Alquist Hospital Seismic Safety Act, expanded by SB 1953 in 1994. Buildings are classified by collapse risk, and every hospital building that doesn’t meet the required performance level must be retrofitted, replaced, or removed from acute care service by January 1, 2030. The state enforces the law directly, and it applies to every acute care hospital regardless of local ordinance.
What Happens If You Ignore an Order
Enforcement varies by ordinance, but the tools typically include administrative citations, daily fines, recording the violation against the property title, and in the worst case, the building department declaring the structure unsafe and ordering it vacated. For a rental property, a vacate order usually costs far more than the retrofit would have. Lenders and insurers also track compliance, so selling or refinancing a flagged property gets difficult before formal penalties even arrive.
Who Designs the Plans and How They Get Approved
Structural plans for buildings subject to seismic design must be prepared and signed by a licensed professional. For most buildings, a licensed civil engineer or architect can stamp them. California also maintains a separate Structural Engineer (SE) license that requires an active California Civil Engineer license and passage of the NCEES PE Structural Exam, which specifically tests high-seismicity design.8BPELSG. Structural Engineer Application For hospitals, public schools, and certain other essential structures, California law requires an SE, not just a civil PE, to prepare and sign the structural design.
The submission package to the local building department includes architectural drawings, structural plans with engineering calculations, and a geotechnical report giving the soil parameters used in design. Municipal plan reviewers, who are themselves licensed engineers, check everything from the lateral system to the anchorage details on nonstructural components. Review ends in either approval or correction notices requiring revision. Only after full approval does the building department issue the permit.
Tall buildings and structures using unconventional systems trigger additional independent peer review. In Los Angeles, buildings using performance-based seismic design (sophisticated computer modeling instead of prescriptive code formulas) must go before a Seismic Peer Review Panel established by the building department. The panel must include a geotechnical engineer with ground-motion expertise and a practicing structural engineer experienced in performance-based design and nonlinear analysis. Buildings over 40 stories or with unusual systems also require an academic researcher on the panel.9LADBS. Alternative Design Procedure for Seismic Analysis and Design of Tall Buildings and Buildings Utilizing Complex Structural Systems This adds months and significant cost.
The Money Side
How the IRS Treats Retrofit Costs
The IRS treats seismic retrofit work as a capital improvement, not a deductible repair. Adding expansion bolts to anchor a building’s frame to its foundation, for example, increases structural strength and must be capitalized. The cost is added to the property’s adjusted basis rather than deducted the year it’s spent.10Internal Revenue Service. Tangible Property Final Regulations That higher basis reduces taxable gain when you sell. For business property, the capitalized cost can be recovered through depreciation over the building’s remaining useful life. If you receive a qualified disaster mitigation payment from a government program to fund part of the retrofit, you cannot increase your basis or take a deduction for the portion paid with those funds.11Internal Revenue Service. Publication 547 (2025) Casualties, Disasters, and Thefts
SBA Disaster Loans
After a federally declared disaster, the Small Business Administration’s Disaster Loan Program can fund repairs and mitigation measures against future earthquakes. For homeowners, the loan can cover building code upgrades up to $500,000, with the mitigation portion capped at the lesser of actual cost or 20 percent of the verified loss. Interest rates are capped at 4 percent for borrowers who cannot obtain credit elsewhere and 8 percent for those who can, with repayment terms up to 30 years. The SBA charges no points, closing fees, or servicing fees on disaster loans.12eCFR. Title 13 Part 123 Disaster Loan Program Businesses get similar terms, though the maximum repayment term drops to seven years if credit is available elsewhere. These loans are only available after a disaster declaration, not for proactive pre-earthquake retrofitting.
Insurance
Standard homeowners and commercial property insurance in California does not cover earthquake damage. Separate earthquake coverage is available through the California Earthquake Authority or private insurers, and premiums are influenced by construction type, age, and whether the building has been retrofitted. At the community level, insurers use the Building Code Effectiveness Grading Schedule (BCEGS), which rates jurisdictions on a 1-to-10 scale based on code enforcement rigor. Communities with strong scores can see lower insurance loss costs, and property owners in those jurisdictions may see reduced premiums or deductibles. A completed retrofit can improve insurability and lower coverage cost where earthquake insurance is available.