Does the WUI code apply to you? Zones, buildings, remodels

California's wildfire-hardening rules used to be scattered across several code books. For the 2025 cycle the state gathered them into one place: a standalone California Wildland-Urban Interface Code (Title 24, Part 7), effective January 1, 2026. Before you hire a designer or price a job, the first question isn't which rule applies — it's simpler than that: does this code touch your address and your project at all? Here's how to answer it in about five minutes.

It's its own book now

The wildfire construction provisions that used to live inside other Title 24 books now sit together in Part 7. It carries its own cover — a separate Emergency Supplement, not one of the parts in the January 2026 errata bulletin (IB 26-01) that corrected the Building, Residential, Fire, and other codes. That's a bookkeeping detail with a practical edge: if you're hunting for the wildfire rules inside the old Building Code chapter, you're looking in a book that no longer holds them. (For the roofing-citation cleanup that came with the move, see our post on reroofing in a fire hazard zone.)

First question: is your address in scope?

Part 7 applies in Fire Hazard Severity Zones. Chapter 3 puts the mapping in one authority's hands: the State Fire Marshal classifies lands into Fire Hazard Severity Zones — under Public Resources Code §§4201–4204 for State Responsibility Areas, and under Government Code §§51175–51189 for Local Responsibility Areas (§302.1). So the map covers both the state-protected backcountry (SRA) and city and county fire-protection turf (LRA). Being inside city limits does not put you out of reach.

The code pins the SRA map to a specific date. The definitions chapter incorporates by reference the map titled "State Responsibility Area Fire Hazard Severity Zones," dated September 29, 2023. A wildland-urban interface area, in turn, is a geographical area the state has identified as a Fire Hazard Severity Zone under those same statutes — plus other areas the enforcing agency designates as being at significant risk from wildfires. That last clause matters: your jurisdiction can pull in territory the state map alone doesn't show.

These lines also move. The code official is directed to reevaluate the WUI areas on a five-year basis (§302.2), timed to coincide with the state's five-year review of State Responsibility Area lands. A parcel that's out today can be in after the next update — so check your address against the current adopted map with your local jurisdiction, not last cycle's.

Second question: is your building the kind the code covers?

Scope is broad. Section 501.1 says buildings and structures in a wildland-urban interface area shall be constructed in accordance with the California Building Code and this code. The code's main target is the applicable building — one with a residential, commercial, educational, institutional or similar occupancy use.

There's a narrow break for small outbuildings. Section 501.1 exempts Group U accessory structures not exceeding 120 square feet where located at least 50 feet from applicable buildings, plus Group U agricultural buildings at least 50 feet away. Miss either number — larger than 120 square feet, or closer than 50 feet — and that exemption is gone.

When a remodel triggers it

Here's the part that trips up owners of existing homes. The code does not force you to retrofit a standing house just because the map now covers it. Under §102.8, the legal occupancy or use of a structure existing on the date of adoption may continue without change — except as is specifically covered in this code.

And modifications are exactly what's specifically covered. The ignition-resistant construction rules reach any building hereafter "constructed, modified or relocated into or within" a wildland-urban interface area.

Verified against the live Part 7 code text: that "constructed, modified or relocated into or within" trigger lives in §503.1 — not the §501.1 scope line. §501.1 states the general scope; §503.1 is the clause that pulls a modification into Chapter 5's requirements.

Roofs get their own trigger. Under §507.1, replacing the roof covering on an existing building — or replacing 50 percent or more of it within a 12-month period — means the new covering must meet the requirements for new construction. And any roof covering applied during an addition, alteration or repair must meet at least a Class A fire classification.

Put those together and the picture is clear: an existing building keeps its grandfathered use, but the day you modify it, relocate it, reroof it, or add on, the new work comes into scope. How far a given "alteration" reaches is a judgment your building official makes — confirm the trigger with your local jurisdiction before you scope the job. None of this is legal advice.

What CrossBeam does with it

CrossBeam tells you up front whether an address sits in a Fire Hazard Severity Zone and whether a given scope of work trips Part 7 — before anyone draws a plan or writes a check. It keeps the broad "new construction" rule separate from the narrower triggers for remodels, reroofs, and additions, so you know which requirements actually attach to your project.