Defensible space: the landscaping rules fire codes impose

The zones are not the same object in every state

“Defensible space” is a landscaping rule imposed by fire codes. It is the buffer a jurisdiction requires between a structure and the plants, mulch, fences and stored fuel that could carry fire to it. The popular diagram — Zone 0 at 0–5 feet, Zone 1 at 5–30, Zone 2 at 30–100 — is a communications template. It is not a statute.

California’s current administrative code still uses two zones: Zone 1 from the structure to 30 feet, Zone 2 from 30 to 100, both capped at the property line (14 CCR § 1299.03). The 5-foot ember-resistant band is a third zone the Legislature added in 2020 (AB 3074) and has spent six years trying to specify. The International Wildland-Urban Interface Code, which Utah, Nevada’s fire marshal, Oregon’s model code, Austin and Boulder all draw from, does not use “Zone 0” at all. IWUIC Table 603.2 sets a single fuel-modification distance by hazard class — Moderate 30 ft; High 50 ft; Extreme 100 ft — and then regulates trees, groundcover, firewood and LP-gas inside that distance.

HyreYard analysis: collapsing those systems into one 0 / 5 / 30 / 100 diagram makes a national page easy to write and wrong to use. The information a homeowner can act on is which instrument applies to the parcel, whether it covers existing yards or only new permits, and what it says about the first five feet — because that is where embers land, and that is where the plant, mulch and fence rules actually change.

Zone 0 is the information gain, and California’s is not in force

Zone 0, also called the ember-resistant zone or the immediate ignition zone, is the band immediately against the structure. IBHS laboratory burns and post-fire investigations have made the same point for a decade: most structure loss in wind-driven wildfires starts with embers, not a flame front, and the first five feet is where embers collect against siding, under decks and at the base of a wood fence. That is a research finding. It is not, by itself, a landscaping ordinance.

Source fact — California statute. Public Resources Code § 4291(a)(1)(A), as amended by Stats. 2025, ch. 731 (AB 1455, effective 13 October 2025), requires 100 feet of defensible space in the State Responsibility Area, “with more intense fuel reductions being utilized between 5 and 30 feet around the structure, and an ember-resistant zone being required within 5 feet of the structure, based on regulations promulgated by the board.” Government Code § 51182 says the same thing for occupied dwellings in locally designated Very High Fire Hazard Severity Zones. A structure for Zone 0 purposes includes an attached deck (PRC § 4291(i); Gov. Code § 51182(e)).

Source fact — California regulation, 5 September 2026. The Board of Forestry and Fire Protection voted on 19 August 2026 to adopt emergency regulations adding 14 CCR §§ 1298.01–1298.04 (Local Responsibility Area VHFHSZ) and amending §§ 1299.01–1299.03 (State Responsibility Area). The package was filed with the Office of Administrative Law on 28 August 2026 as file 2026-0828-03E, subject “Zone 0 Defensible Space.” The five-day comment period closed on 2 September 2026. As of 5 September 2026 we found no OAL approval published and no Secretary of State filing. 14 CCR § 1299.03, the regulation CAL FIRE actually inspects against, still defines two zones.

Source fact — statutory delay, even after OAL. PRC § 4291(g)(1) says the ember-resistant-zone requirement “shall not take effect for new structures until the board updates the regulations… and the guidance document.” Subsection (g)(2) says it takes effect for existing structures three years after the new-structure date. Subsection (h) says the department shall not change inspection practices or forms until the State Fire Marshal posts a written finding that the Legislature has appropriated enough money to do so. A Board vote is not the end of that chain.

HyreYard analysis: anyone currently selling “California Zone 0 compliance” as a statewide legal duty is selling ahead of the CCR. Anyone saying Zone 0 “isn’t real” is ignoring a statute that has required the Board to write it since 2020, a unanimous Board vote in August 2026, and a stack of local ordinances that did not wait. The accurate sentence is the long one: the duty is in the code books as a regulation-dependent requirement; the regulation was adopted by the Board and is sitting with OAL; the current inspectable standard is still Zone 1 and Zone 2.

What may be planted, mulched or fenced against the structure

The first five feet is where the landscaping rule stops being “thin the brush” and starts being “change the materials.” Where a Zone 0 or Ember Ignition Zone is actually in force, the pattern is consistent even though the section numbers are not: hardscape or bare mineral soil; no wood mulch; no firewood; no juniper against the siding; the first run of fence, if the code mentions it, in a noncombustible material.

City of Boulder, Colorado — in force on new work. Boulder Revised Code chapter 10-8.5, section 603.2.4, requires a five-foot noncombustible zone around new buildings, decks and additions: no vegetation and no combustible material. Section 603.2.6 bans planting any Juniperus species on or after 1 August 2025, citywide, and requires juniper removal as a condition of new-development permits. The Landscape Manual’s WUI mulch table is more specific than most fire codes: squeegee gravel is allowed in the noncombustible zone; aged arbor-chip mulch is not; cedar bark and “gorilla hair” mulches are prohibited in all WUI ignition-risk areas. New fences and walls within 8 feet must be noncombustible.

City of Austin, Texas — in force on WUI parcels. Austin’s 2024 IWUIC § 603.2.1, in effect for applications on or after 10 July 2025, is the cleanest municipal Zone 0 specification in this table. Five feet from the roof overhang, gravel or pavers, no plants, no combustible furniture, no artificial turf. Protected and Heritage trees on existing buildings are excepted — the Ember Ignition Zone is not a tree-removal permit. Proximity Zone C may use perennial, green, closely mowed lawn instead of hardscape. Ignition-resistant fence is required within 10 feet in Zones A and B and within 5 feet in Zone C.

Town of Truckee / Truckee Fire Protection District, California — in force as an inspection criterion. Truckee Fire publishes Zone 0 as 5 feet horizontally and vertically from any structure, with no combustible bark or mulch, and requires the inspection for real-estate transfers, short-term rentals and building-permit finals. The Town Development Code already prohibits landscaping, including combustible mulch, within five feet vertically and horizontally of any building. The numbered district ordinance on the website is still 02-2012; the Zone 0 criteria are what inspectors are scoring in 2026. Ask the District which text governs a given inspection.

Colorado (statewide) — in force on new construction. The 2025 Colorado Wildfire Resiliency Code, 8 CCR 1507-39, Structure Ignition Zone 1: noncombustible hard surface, tree crowns at least 10 feet from the structure, ignition-resistant plants only. Fencing within 8 feet: noncombustible or ignition-resistant. It is not a retrofit of existing Front Range yards. Locals (Boulder County IRC § R390.4.12.1 is a 5-foot gravel-and-weed-barrier perimeter on a building permit) can and do apply a 0–5 foot rule at permit.

Oregon (statewide) — in the model, not on the street until adopted. The 2026 Oregon Defensible Space Model Code § 301.2 is a five-foot noncombustible band that names bark mulch as a prohibited fuel. OAR 837-040-0030 lets a local government elect to adopt it. Until that election, OSFM’s homeowner guidance is education.

California (statewide) — in the statute, not in the CCR. Until OAL publishes the Board package and the guidance-document gate in PRC § 4291(g) is met, the inspectable plant and mulch rules are Zone 1 and Zone 2 in 14 CCR § 1299.03: dead fuel out of the first 30 feet, firewood covered or moved, 4-inch grass and 3-inch litter in Zone 2. Local overlays (Los Angeles County’s named flammable ornamentals, the City of Los Angeles’s 200-foot brush standard, Truckee’s 5-foot mulch ban) are already stricter than the state CCR.

44,100,000 WUI houses is not 44,100,000 covered households

The contract for this page asked us to join the rules table to the SILVIS Lab wildland-urban interface dataset so the covered household count would be a number rather than an impression. We retrieved the number. We are not going to misuse it.

Source fact. Radeloff, Mockrin, Helmers and colleagues mapped the conterminous-US WUI from Census housing and National Land Cover Data for 1990–2020, using the Federal Register definition (66 Fed. Reg. 751). As of 2020, 9.4% of CONUS land area was WUI, and that land held more than 44,100,000 homes — 32% of US housing. Housing in the WUI grew 46% from 1990 to 2020; area grew 31%. The 2010s added 2,600,000 WUI houses. California held 5,100,000 WUI houses in 2020 and added 244,000 in the 2010s; Texas held 3,200,000 and added 534,000 (Radeloff et al., Science 382:702–707, 2023; USFS Research Data Archive RDS-2015-0012-4).

HyreYard analysis — why we do not join. WUI is a geographic class: houses at densities that meet or intermingle with wildland vegetation. PRC 4291 is a legal class: buildings in the State Responsibility Area. Government Code 51182 is a different legal class: occupied dwellings in a locally designated VHFHSZ. Oregon no longer has a statewide map. Washington’s maps were not final on the retrieval date. Colorado’s code applies to new construction in a Board-mapped WUI. Texas’s 3.2 million WUI houses are not 3.2 million houses under a clearance ordinance — Texas has no statewide one. Publishing “44,100,000 households covered” would be a category error with a large, citable-looking denominator. The honest sentence is: tens of millions of American houses sit where vegetation meets development, and only a minority of states have written a statewide landscaping duty that follows.