Planning Your Project
My address is in a fire hazard zone now. What changes for an ADU or an addition?
The maps changed in 2025, the code changed name on 1 January 2026, and a five-foot rule around the building is about to change the landscaping. Here is what is actually required.
Three things changed and they stack. In 2025 the State Fire Marshal redrew the fire hazard maps for cities and towns, and places like Los Gatos, Saratoga, Los Altos Hills, the Palo Alto foothills and the Woodside Fire district adopted them that summer. On 1 January 2026 the old Chapter 7A wildfire construction rules were deleted from the Building Code and reissued as the California Wildland-Urban Interface Code, Title 24 Part 7, and an emergency amendment made them apply in High zones inside city limits, not just Very High. And in August 2026 the Board of Forestry adopted the first Zone 0 rules for the five feet around a structure. If your parcel is in a mapped zone, a new ADU, a new house, and from 2026 an addition or exterior remodel, are built to Part 7: Class A roof, ember-resistant vents, protected eaves, tempered glazing, and a vegetation plan signed off before final.
What happened in 2025, and why your address may have moved
California maps fire hazard in two layers. In the State Responsibility Area, the unincorporated wildland CAL FIRE protects, the maps have been in force since April 2024. In the Local Responsibility Area, which is every city and town plus the urban county pockets, the Office of the State Fire Marshal issued new recommended maps in four regional batches between 10 February and 24 March 2025. The batch covering Santa Clara and San Mateo counties was released on 24 February 2025 (OSFM, 2025 LRA rollout).
Under Government Code §51178 and §51179 each city and county then had 120 days to adopt the zones by ordinance. A local agency may add parcels to a higher class; it may not remove them. Since SB 63 (2021) the adoption covers all three classes, Moderate, High and Very High, where before 2025 cities only had to designate Very High. That is why so many South Bay and Peninsula parcels that were never in a zone now carry a colour.
- Los Gatos adopted its map by Ordinance 2374 on 17 June 2025. The hills west of Highway 17 and above Lexington Reservoir stay Very High; neighbourhoods south of Town Hall became High; some areas dropped to Moderate.
- Saratoga adopted in June 2025, with some hillside areas moving from Very High to High or Moderate, to the concern of residents who wanted the stricter label kept.
- Los Altos Hills first voted in May 2025 to add roughly 50 parcels beyond the state recommendation, then reversed on 20 June 2025 and adopted the CAL FIRE base map. Town documents put about 507 parcels in the Very High zone.
- Palo Alto has more than 130 homes in its Very High zone in the foothills. Woodside, Portola Valley, Emerald Hills and Ladera, served by the Woodside Fire Protection District, have roughly 150 to 200 parcels in Very High.
The counts above are from the towns' own documents and local reporting as of September 2026 and they will drift. What does not drift is the method: look your address up on the OSFM viewer, then ask your city for its adopted map, because a city may have added parcels the state viewer does not show.
The State Fire Marshal is explicit: the maps rate hazard, meaning the physical likelihood and expected behaviour of fire over a 30 to 50 year horizon from fuel, slope, wind and weather. They give no credit for a hardened house, a cleared yard or a recent burn. A Very High parcel with a Class A roof and five feet of gravel is still a Very High parcel on the map, and the code treats it that way.
The rulebook changed name on 1 January 2026
For eighteen years the construction standard for fire zones was Chapter 7A of the California Building Code, with a twin at Section R337 of the Residential Code. In the 2025 code cycle the Building Standards Commission deleted Chapter 7A and relocated every one of its provisions into a new volume, the California Wildland-Urban Interface Code (CWUIC), Title 24 Part 7, Chapter 5 (BSC, 2025 Title 24 code changes). It took effect on 1 January 2026.
Two things rode along with the move. First, an emergency amendment approved in October 2025 expanded the code's application to High Fire Hazard Severity Zones in Local Responsibility Areas, also effective 1 January 2026. Until the end of 2025 the mandatory trigger inside a city was Very High only. Second, the scope section (CWUIC §501.1) applies the code to new buildings, and to additions, alterations and repairs to existing buildings for which a permit application is submitted on or after 1 January 2026, in any Fire Hazard Severity Zone or designated wildland-urban interface area.
Pages that say "Chapter 7A applies in Very High zones" were correct until 31 December 2025. From 1 January 2026 the citation is Title 24 Part 7 Chapter 5, it applies in High zones inside cities as well, and it reaches additions and exterior remodels, not only new buildings. A plan set or a bid that still cites 7A was drawn against the old rule.
What the code actually asks of the building
Part 7 Chapter 5 is a list of components, each with a tested or listed way to build it. The Office of the State Fire Marshal summarises the sections on its Building in the Wildland page. In builder's terms:
| Section | Component | What it means on site |
|---|---|---|
| 504.2 | Roofing | Class A roof assembly; openings at the eave and ridge closed against embers |
| 504.3 | Eaves | Enclosed soffits, or an exposed underside built from noncombustible, ignition-resistant or fire-retardant-treated material |
| 504.4 | Gutters | Means to stop leaves and debris accumulating in the gutter |
| 504.5 | Exterior walls | Ignition-resistant or noncombustible cladding, or a tested assembly, from grade to the roof |
| 504.6 | Underfloor enclosure | Raised floors and under-deck areas enclosed or built to the standard |
| 504.7 | Projections and decks | Deck boards, stair treads and attached structures from listed materials |
| 504.8 | Glazing | Tempered or multi-pane glass in windows, doors and skylights |
| 504.9 | Exterior doors | Rated or noncombustible doors, including garage doors |
| 504.10 | Vents | Ember-resistant, listed attic, eave and underfloor vents |
| 504.11 | Accessory structures | Sheds and detached structures within the set distance built to match |
Then one line that sits outside the building: before the final inspection is signed the property must comply with the code's vegetation management requirements (CWUIC Appendix B). In a Very High zone that pairs with the long-standing 100-foot defensible space rule under Government Code §51182. Your yard is part of the permit.
Zone 0: the five feet nobody budgets for
AB 3074 (2020) and SB 504 (2024) told the Board of Forestry and Fire Protection to define an ember-resistant zone in the first five feet around a structure, and Executive Order N-18-25 set a deadline. The Board adopted the Zone 0 regulations on 19 August 2026. They apply in the State Responsibility Area and in Very High zones inside cities. New construction must comply as soon as the rules take effect; existing homes get a phase-in that the Board's materials describe in three and five year steps (Board of Forestry, Zone 0). As of this writing the Board says the package is still completing its final review with the Office of Administrative Law, so check its page for the operative date rather than taking a secondary source's word for it.
The Woodside Fire Protection District did not wait: its own 2024 ordinance already applies Zone 0 to every home in the district, zone or not, and it has been inspecting in Woodside with Portola Valley to follow.
For a new ADU or addition the design consequence is concrete. Nothing combustible inside five feet of the walls, decks or stairs: no bark mulch, no wood fence tied to the building, no combustible gate, no planters against the siding. A detached ADU set four feet off a wooden property-line fence is a Zone 0 problem the day it is finished. Site the unit, or specify the fence, with that in mind.
Points specific to ADUs
- State ADU law does not carve out fire zones. The ministerial approval, the size floors and the setback rules in Government Code §66314 still apply on a Very High parcel. What changes is how the unit is built, not whether it may be.
- A new detached ADU is a new building under Part 7. Every row in the table above applies, and the vegetation plan is a condition of final.
- Sprinklers are a separate question. Whether the ADU needs a fire sprinkler system turns on whether the main house has them, not on the hazard zone; see our sprinkler guide. Fire-district review of access and water supply is a third question again, and in the hills it can be the expensive one.
- SB 9 lot splits treat Very High zones differently. If the plan is a split rather than an ADU, read the SB 9 guide first.
What to do before anyone draws anything
Look the parcel up
OSFM viewer first, then the city's adopted 2025 map. Write down the class and the date you checked. The class decides which code applies and whether Zone 0 reaches you.
Tell the designer on day one
Part 7 Chapter 5 changes the window schedule, the vent schedule, the siding, the deck framing and the roof assembly. Those belong on the first set, not in a plan-check correction.
Price the fire package as its own line
Tempered glazing, listed vents, ignition-resistant cladding and a Class A assembly are each a real line. A bid that does not break them out has either missed the zone or buried it.
Plan the yard with the building
Five feet of noncombustible ground, fence material at the building, and the defensible space plan the inspector will want to see at final.
Ask your insurer what they will want
We do not give insurance advice. We do know that a hardened new structure is a different conversation with a carrier than an unhardened one, and it is a conversation to have before the permit, not after.
We build in these hills. On a Project Discovery Call for a Los Gatos, Saratoga, Los Altos Hills, Woodside or Portola Valley lot, the zone lookup is the first thing we do, because it changes the scope before the scope exists.
Common questions
Does Chapter 7A still apply to homes in fire hazard zones in California?
Do the wildfire building rules apply in High zones inside a city, or only Very High?
Can I still build an ADU on a lot in a Very High Fire Hazard Severity Zone?
When did the fire hazard maps change for Santa Clara and San Mateo counties?
What is Zone 0 and does it apply to my house?
Where to go next
Written by the team at Elusive Construction, a licensed California general contractor (B #1112902) building in Santa Clara and San Mateo counties. General information about how residential construction works — not legal advice. For your specific contract, talk to an attorney.
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