Building an ADU in a
fire hazard zone.

The direct answer

Yes, you can generally build an ADU in a High or Very High Fire Hazard Severity Zone. What changes isn't whether you can build — it's what the structure has to be built with and how it has to sit on the lot.

What "ignition-resistant construction" actually requires

California's building code already imposes ignition-resistant construction standards — Chapter 7A of the California Building Code — for new construction in Wildland-Urban Interface Fire Areas. In practice that means Class A fire-rated roofing, ember-resistant vents, dual-pane tempered windows, and non-combustible siding. These aren't upgrades you can skip to save budget; they're code minimums for the zone.

The defensible-space setback, specifically for ADUs

ADUs sited in High or Very High Fire Hazard Severity Zones must maintain a minimum four-foot setback from adjacent native or naturalized vegetation, specifically to create defensible space between the structure and anything that could carry fire toward it. This is separate from the standard property-line setback rules and applies on top of them.

Defensible space around the whole property

If your property sits in a State Responsibility Area, state law requires 100 feet of defensible space around structures generally, not just the new ADU — vegetation management and clearance that affects your whole lot, not just the footprint of what you're building.

One rule still moving through rulemaking, not yet settled

CAL FIRE has proposed a "Zone 0" standard that would require the 5 feet immediately around a structure to be cleared of combustible mulch, stored firewood, and flammable plants in Very High Fire Hazard Severity Zones specifically. As of now this is a proposed regulation still moving through the Board of Forestry's rulemaking process — worth knowing about and planning for, but not yet a code requirement you're bound to today.

What this means for your project

Building in a fire hazard zone costs more, mostly in materials and siting, not in permitting difficulty — the approval process itself doesn't change. We confirm your property's actual fire hazard zone designation and the specific standard it triggers before pricing your ADU, so the fire-rated materials and setback are in the budget from the start, not discovered as a change order once plan check flags them.