Guide
Fire hazard zones after the 2025 maps: what changes for ADUs, additions and rebuilds
The short answer
In 2025 the state mapped fire hazard zones in cities at three levels, and the City of San Diego's map took effect on August 30, 2025. On a mapped City lot, new buildings, additions and exterior changes to regulated features must meet the wildfire building standards, and a new ADU in a Very High zone keeps at least 4 feet from the side and rear lines. The City's own Zone 0 rule covers new buildings whose permits are applied for from February 28, 2026. The state's version is not yet in effect.
What the 2025 maps changed
Fire hazard severity zones describe hazard, not risk. They rate the fire behavior a place can expect over decades, without counting defensible space or a hardened house, in three classes: Moderate, High and Very High.
Cities used to be mapped for Very High zones only. A 2021 law, SB 63, added the Moderate and High classes there, and the State Fire Marshal released the new local maps in four phases in early 2025. San Diego's came on March 24, 2025.
State law then gave the City 120 days to adopt the recommended map by ordinance. A city may add areas or raise a zone's level, but it may never lower one.
The City of San Diego adopted Ordinance O-21992 on July 29, 2025, effective August 30, 2025. It designates the state's recommended areas, plus more areas its fire department found at significant risk, as Very High Fire Hazard Severity Zones on one City map. If any part of your lot falls inside the mapped zone, the City applies the wildfire building standards to your project.
Other cities adopt their own maps under the same law. Del Mar adopted its map in June 2025 and says its High and Very High areas grew significantly, taking in neighborhoods next to open space.
What a zone means when you build
Building in a zone means meeting California's wildfire construction standards for the outside of the building, such as roofing, vents, siding, windows and decks. For years they sat in Chapter 7A of the Building Code and Section R337 of the Residential Code. The 2025 codes, in force since January 1, 2026, moved them into a new California Wildland-Urban Interface Code, where Chapter 5 holds them.
Statewide, the Fire Marshal's FAQ says these standards apply to new buildings in High and Very High zones in cities, and that a local ordinance can extend them to remodels. The City of San Diego applies them to new buildings, to additions and to exterior alterations that touch a regulated feature. Del Mar applies them to new construction in its High and Very High zones.
| Project | What applies |
|---|---|
| New detached ADU | The wildfire building standards, side and rear setbacks of at least 4 feet at any height, more setback if the Fire Code Official or the Brush Management Zone calls for it, and Zone 0 around the new building. |
| Bonus ADUs under the City's density bonus program | The lot must front an improved public street with at least two evacuation routes, and may not front a cul-de-sac or rely on a single way in and out. |
| Addition | The wildfire building standards for the new work. |
| Exterior remodel | The standards for the regulated features you change, such as windows, siding or a deck. |
| Rebuild or new house | The standards for the whole building, Zone 0 as a new structure, and the new code's siting rules, which start from a 30-foot setback from property lines and the road's center line and allow reductions for small or steep lots and other constraints. |
| Existing home, no work planned | Defensible space clearance out to 100 feet, and Zone 0 from February 28, 2027, enforced in phases to 2029. |
| Selling | A natural hazard disclosure. In High and Very High zones state law also asks for a record of a defensible space inspection, as Del Mar's page explains. |
ADUs in the City: the 4-foot setback and the bonus rules
Where no fire zone applies, the City lets a detached ADU up to 16 feet tall sit as close as the building and fire codes allow to the side and rear property lines. Inside a Very High Fire Hazard Severity Zone, the ADU stays at least 4 feet back on those sides at any height, to leave defensible space, and the Fire Code Official can ask for more.
The code's wording is High or Very High, but O-21992 designates every mapped fire zone in the City as Very High, so check your lot on the City's fire map. In a Very High zone, bonus ADUs also need a lot on an improved public street with at least two evacuation routes, and can't go on a cul-de-sac or a lot with only one way in and out. On a coastal lot these 2025 rules wait on Coastal Commission certification, so ask the City at intake which setback applies.
Zone 0: the first 5 feet around a building
Zone 0 is the ember-resistant strip within 5 feet of a building. A 2020 state law, AB 3074, told the Board of Forestry and Fire Protection to write rules for it in Very High zones in cities and across the State Responsibility Area.
The City of San Diego wrote its own. Ordinance O-22042, the City's version of the new Wildland-Urban Interface Code, took effect on February 28, 2026. It keeps plants, mulch, firewood and other things embers can ignite out of Zone 0, for any new structure whose permit application comes in from that day, and for existing structures one year later.
For existing homes, the City's fire department guidelines (revised April 22, 2026) say nothing is required yet: the first year is education, enforcement starts on February 28, 2027 and builds in phases, and full compliance is the goal by February 28, 2029. Sheds and other outbuildings within 5 feet must be noncombustible or ignition-resistant, and a fence or gate attached to the house needs a noncombustible span for its first 5 feet.
The Board adopted statewide emergency Zone 0 rules on August 19, 2026. Its guidance document leaves their effective date blank.
Inside the City, the City's own dates are the ones to plan around. State law lets a city set stricter fire rules of its own, and the Board's guidance lists the City of San Diego among the places that already have a local Zone 0 rule.
The state's rules are not in force. The Board withdrew them from the state's legal review on September 8, 2026, and no new filing was listed when we checked on October 19, 2026. Once they take effect, they apply right away to new buildings, and existing homes get three years, or up to five for some steps on a local timeline, unless a refiled version changes that.
Elsewhere in the county, your city or fire district may have a rule of its own, and the unincorporated County's 2026 fire code already calls for noncombustible materials in the first 5 feet. Ask your local fire agency which rule applies to your lot.
Defensible space, selling and insurance
- Clearance. In a Very High zone, state law calls for defensible space out to 100 feet from buildings, and the City adds its own brush management rules.
- Selling. You make a natural hazard disclosure, and in High and Very High zones state law also asks for a record of a defensible space inspection, as Del Mar's page explains.
- Insurance. The City's FAQ notes that insurers use their own risk models rather than the hazard maps, though much of the same data feeds both, and its Zone 0 guidelines warn that an insurer may ask for more than the City does.
What changes the answer
The rules above are the City of San Diego's unless named otherwise. These are the cases where the answer moves.
Another city
Each city adopts its own map under state law and may add areas to the state's. Del Mar applies the wildfire building standards to new construction in its High and Very High zones and runs its own inspections.
The State Responsibility Area
Where the state handles wildfire protection, its own maps have applied since April 1, 2024, the wildfire building standards apply at every hazard level, and the Board's Zone 0 rules would reach every building once in effect.
The Coastal Overlay Zone
The City's 2026 ADU amendments, O-22109, do not apply in the Coastal Overlay Zone until the Coastal Commission certifies them, so a coastal lot may still be under the older ADU wording.
A historic building
Under the City's Zone 0 guidelines a historic structure may use other measures of equal fire protection, backed by a technical report, or sign an affidavit when strict compliance would conflict with preservation.
A lot in the Brush Management Zone
The Fire Code Official can require larger ADU setbacks there than the 4-foot minimum.
Next steps
Check your lot on the map, then see what your project needs.