California’s Title 24 building code requirements are the statewide minimum rules for how buildings must be designed and constructed, covering structural safety, fire resistance, electrical and plumbing systems, energy performance, and green building measures. The 2025 edition took effect on January 1, 2026, and applies to new construction, additions, and most remodels across the state.1California Department of General Services. California Building Standards Commission – Codes Local building departments enforce the code and can adopt stricter rules on top of it, but they cannot weaken the state baseline. If your project does not meet Title 24, you will not get a permit, and if you build without one, you can face misdemeanor charges, stop-work orders, and civil penalties.
What Title 24 Covers
Title 24 of the California Code of Regulations is published by the California Building Standards Commission and updated on a three-year cycle.1California Department of General Services. California Building Standards Commission – Codes It is divided into twelve parts. Three come up most often for property owners:
- The California Residential Code (Part 2.5) governs one- and two-family dwellings and townhouses, including the structural, plumbing, mechanical, and electrical rules specific to homes.
- The California Electrical Code (Part 3) sets minimum standards for electrical design and installation to prevent fire and shock hazards.2Division of the State Architect. Overview – Title 24 Building Standards Code as Adopted by the Division of the State Architect
- The California Green Building Standards Code (Part 11), known as CALGreen, mandates sustainability measures for residential and commercial projects, from water-efficient fixtures to construction waste diversion.2Division of the State Architect. Overview – Title 24 Building Standards Code as Adopted by the Division of the State Architect
The remaining parts cover the Fire Code, Plumbing Code, Mechanical Code, Energy Code, and others. Because a city or county can impose tougher requirements, a design that satisfies Title 24 may still need to meet local overlays. Check with the building department where your project sits before you lock in plans.
Seismic Design and Fault-Zone Rules
Earthquake risk drives much of what California requires. Every building gets a Seismic Design Category under the code, based on its occupancy type and the expected ground motion at the site. Essential facilities such as hospitals and fire stations fall into the most demanding categories. Two site-specific state laws layer additional requirements on top of the code itself.
Alquist-Priolo Earthquake Fault Zoning Act
The Alquist-Priolo Act, passed in 1972, restricts construction of occupied structures across the traces of active faults. If your parcel sits in a designated fault zone, the local agency cannot approve a development project until you submit a geologic report from a licensed professional evaluating the risk of surface rupture. The agency can waive the report only with the State Geologist’s approval.3Justia Law. California Public Resources Code Chapter 7.5 – Earthquake Fault Zoning
Smaller projects get some relief. Single-family wood-frame or steel-frame homes of two stories or fewer are generally exempt when they are not part of a development of four or more units. Alterations and additions valued at less than 50 percent of the existing structure’s value are also exempt.3Justia Law. California Public Resources Code Chapter 7.5 – Earthquake Fault Zoning
Seismic Hazards Mapping Act
The Seismic Hazards Mapping Act addresses liquefaction and earthquake-triggered landslides. If your property falls within a designated Zone of Required Investigation, the building department will require a site-specific geotechnical investigation before issuing a permit. A licensed engineering geologist or civil engineer must conduct it and recommend specific measures to reduce the hazard. The agency sends an approved copy to the state within 30 days.4California Department of Conservation. California Seismic Hazard Zones The same small-home exemption applies.
Wildfire Zone Construction
If your property sits in or near a designated Fire Hazard Severity Zone, the California Wildland-Urban Interface Code adds material and assembly requirements aimed at the three ways wildfires actually ignite buildings: wind-driven embers, radiant heat, and direct flame contact.5ICC Digital Codes. 2025 California Wildland-Urban Interface Code, Title 24, Part 7 Chapter 7A of the Building Code sets the specifics for new construction and many remodels:
- Roof assemblies must achieve a Class A fire rating. Where roofing profiles leave an airspace over a combustible deck, a mineral-surfaced cap sheet or noncombustible board must fill the gap.
- Ventilation openings must use wildfire flame and ember-resistant vents approved by the State Fire Marshal, with noncombustible corrosion-resistant mesh sized between 1/16-inch and 1/8-inch.
- Exterior glazing must use at least one pane of tempered glass, glass block, or an assembly with a fire-resistance rating of at least 20 minutes.
- Exterior wall coverings must meet ignition-resistance standards, with specific testing or material requirements depending on the cladding type.
Defensible space rules on vegetation clearance apply separately and are not a substitute for the construction requirements.
Energy and Green Building
Two parts of Title 24 carry the sustainability weight: the Energy Code (Part 6) and CALGreen (Part 11).
Solar and Battery Mandates
The Energy Code requires solar photovoltaic systems on newly constructed single-family homes, with limited exceptions for roofs with insufficient area or heavy shading.6California Energy Commission. 2025 Single-Family Solar PV The 2025 edition extends solar requirements to new commercial and multifamily buildings, and new buildings must also include battery energy storage systems or be designed as battery-ready.7California Energy Commission. Solar PV, Solar Ready, Battery Energy Storage System (BESS) and BESS-Ready
CALGreen Mandatory Measures
CALGreen applies to residential and commercial projects and includes mandatory water-efficient plumbing fixtures, indoor air quality controls such as low-emitting adhesives and paints, and construction waste diversion. Many local jurisdictions adopt CALGreen’s voluntary tiers as local requirements, pushing standards above the state baseline.
Federal 45L Credit for Energy-Efficient Homes
Builders of qualifying energy-efficient homes may claim the federal Section 45L tax credit of $2,500 to $5,000 per unit. ENERGY STAR certified single-family and multifamily homes qualify for $2,500 per unit; homes meeting the stricter DOE Zero Energy Ready Home program standards qualify for $5,000. The credit applies to homes acquired before July 1, 2026.8Department of Energy. Section 45L Tax Credits for DOE Efficient New Homes
Permits and Inspections
Almost every construction project in California needs a building permit before work begins. The local building department reviews plans for Title 24 compliance, local zoning, and overlay requirements such as fire or seismic hazard zones. Fees vary. A standard residential addition typically runs from a few hundred dollars for minor work to several thousand for larger projects, and major commercial jobs can see fees in the tens of thousands.
After the permit issues, inspections happen at key stages: foundation, framing, electrical rough-in, plumbing, insulation, and a final check before occupancy. Projects in seismic or wildfire zones can require additional specialized inspections, such as geotechnical evaluations or fire-resistance verification. If an inspector flags a problem, you get a correction notice. Keep working on a failed inspection without fixing the issue and the department can issue a stop-work order.
Some jurisdictions allow third-party inspections for certain components, and certified energy consultants handle Title 24 energy audits. Expedited permitting is sometimes available for projects using pre-approved green building criteria or standardized plan sets.
What Does Not Need a Permit
Exemptions are narrower than most people assume. One-story detached accessory structures used as tool sheds, storage sheds, or playhouses do not require a permit if the floor area stays under 120 square feet and the structure contains no electrical, plumbing, or mechanical systems. Even exempt structures must still comply with zoning setbacks, and in fire hazard zones they may still need to meet Chapter 7A material standards. Some agricultural buildings used exclusively for farming are exempt from standard building permits but still must satisfy zoning and environmental rules. Emergency repairs to immediately dangerous conditions can often proceed first, with a permit applied for after the fact.
Who Can Do the Work
California requires a state contractor’s license for any construction project where the total cost of labor and materials reaches $1,000 or more, or where a building permit is required. The California Contractors State License Board (CSLB) runs the program.9Contractors State License Board. Step 1: Before Applying for the Examination Working without a license is a criminal offense. A first conviction can bring a fine of up to $5,000, up to six months in county jail, or both. Repeat offenders face steeper fines tied to a percentage of the contract price and mandatory minimum jail time.
When a licensed contractor performs work without pulling the required local permit, the CSLB treats that as a separate violation. Penalties include civil assessments of up to $5,000 per violation, an order to pay the permit fees and local penalties, and suspension or revocation of the license.10Contractors State License Board. Filing a Building Permit Violation Form Before signing a contract, verify the license is active through the CSLB’s online lookup.
If You Are Building an ADU
Accessory dwelling units are now one of the most common California construction projects, and state law has aggressively preempted local rules that used to block them. Local agencies must approve qualifying ADU applications ministerially, meaning no discretionary review or public hearing. If the building department does not act on a complete application within 60 days, the application is automatically deemed approved.
State law sets dimensional and regulatory floors that local ordinances cannot undercut:
- Detached ADUs can be up to 1,200 square feet. Attached ADUs can be up to 50 percent of the existing home’s floor area, with a minimum allowance of at least 850 square feet, or 1,000 square feet for units with more than one bedroom.
- Setbacks of no more than four feet from side and rear lot lines apply to new construction. Conversions of existing structures require no setback at all.
- No parking can be required for ADUs near public transit, within historic districts, within existing structures, or in several other common situations. When a garage is demolished or converted to build an ADU, the local agency cannot require replacement parking.
- Local agencies cannot impose minimum lot size requirements for ADUs.
- Fire sprinklers are not required unless the primary residence requires them.
Local governments can still require ADU projects to comply with Title 24 and with zoning setbacks within the limits state law allows. Courts have consistently sided with the state when local ordinances exceed those boundaries.
Penalties for Code Violations
Local building departments find violations through inspections, complaint investigations, and aerial or street-level surveys. Common ones include building without a permit, deviating from approved plans, and using substandard materials. Enforcement usually starts with a notice of violation setting a deadline to correct the problem.
Ignore it, or the violation is serious enough on its own, and the exposure escalates fast. Under California Health and Safety Code section 17995, violating the state’s building standards is a misdemeanor punishable by a fine of up to $1,000, up to six months in jail, or both.11California Legislative Information. California Health and Safety Code Section 17995 A second or subsequent conviction at the same property within five years raises the maximum fine to $5,000.12California Legislative Information. California Health and Safety Code Section 17995.1 Local agencies can also impose administrative fines, issue stop-work orders, and in extreme cases order demolition of unsafe structures.
Civil exposure runs on a separate track. The California Attorney General or local district attorneys can sue repeat offenders for court-ordered corrections and additional monetary penalties. Buyers or tenants harmed by concealed code violations can sue as well. Contractors face CSLB discipline on top of everything else, including civil penalties up to $5,000 per violation and license suspension or revocation.10Contractors State License Board. Filing a Building Permit Violation Form
Historic Buildings
California’s Historical Building Code provides an alternative compliance path for qualified historic structures. Instead of meeting current Title 24 standards exactly, owners can use alternative materials, methods, and designs that preserve the building’s historic character while still providing reasonable safety from fire, earthquakes, and other hazards.13Office of Historic Preservation. State Historical Building Code The building must be listed on a national, state, or local historic register. Approval from the local historic preservation board is required before modifications start, and the alternative approach must be documented and reviewed by the building department.
Owners of federally designated historic buildings may qualify for a 20 percent federal rehabilitation tax credit. The building must be listed in the National Register of Historic Places or certified as contributing to a registered historic district. Rehabilitation costs must exceed the greater of $5,000 or the building’s adjusted basis. The work must follow the Secretary of the Interior’s Standards for Rehabilitation, and the building must be used for income-producing purposes for at least five years after the project is complete. Owner-occupied residences do not qualify.14U.S. National Park Service. Eligibility Requirements – Historic Preservation Tax Incentives
Appealing a Building Department Decision
If the building department denies your permit, cites you for a violation, or takes enforcement action you believe is wrong, you can appeal. Most jurisdictions have a local board of appeals for disputes over technical code interpretations. Broader disputes may go to the city council or county board of supervisors.
When the dispute involves an administrative fine, California Government Code section 53069.4 provides a specific path to superior court. You have 20 days after the local agency serves its final decision to file. The court hears the case as a fresh review of the facts, not just a check on whether the agency followed its own procedures.15California Legislative Information. California Government Code Section 53069.4 The local agency’s file is admitted into evidence, but you can present new evidence and arguments. Case law also recognizes the option of a traditional writ of mandate as an alternative.
Where local rules conflict with state mandates, courts have struck down local restrictions that exceeded what state law allows, particularly in ADU regulation. The 20-day deadline for administrative fine appeals is unforgiving, so talk to an attorney promptly after the final decision arrives.