Radeloff (2005) maps the wildland-urban interface as houses plus wildland vegetation, using a Federal Register definition on census blocks. Intermix is houses in the vegetation. Interface is developed land within 2.4 km of a large vegetated block. That map is not a CAL FIRE FHSZ overlay, not Cohen’s 40 meters, and not Oregon R327.
You are looking at a national WUI web map with your parcel in the orange. That orange is housing density and land cover. It is not a construction overlay, and it is not a burn/no-burn stamp on the house.
No g3-passed exhibit matches this object. ZON-001 is zone bands around one house. Do not reuse it as a census-block WUI map. Do not screenshot Radeloff’s figure.
Why it matters
People treat “in the WUI” as “the forest will take the house.” Radeloff’s layer is where houses and wildland vegetation coincide. He says the Federal Register definition does not explicitly account for fire risk. Cohen says ignition is the house and about 40 meters. FHSZ is a California construction map. Mixing those three is how a Bend lot gets a California overlay, or a mapped WUI lot skips vents.
How the documents split
Object
Spatial unit
What it is not
National WUI (Radeloff 2005)
Census block + NLCD vegetation
A fire-behavior model
Intermix
≥6.17 housing units/km² and ≥50% wildland vegetation
Interface
Interface
Same housing floor, <50% vegetation, within 2.4 km of a ≥75% vegetated block ≥5 km²
AHJ declaration plus fire-intensity class on official maps
Radeloff 2005 or FHSZ
In that 2005 assessment the conterminous WUI was 9 percent of land and 39 percent of houses. California had the most WUI housing units (5.1 million). Eastern states had the most WUI land. Those are 2000-census numbers. They are not today’s permit.
The paths
1. Read the definition. Houses meet or intermingle with undeveloped wildland vegetation. Intermix is mixed. Interface is next door, with a 2.4 km firebrand-flight buffer from the California Fire Alliance (2001) as Radeloff used it.
2. Do not treat it as FHSZ. California CWUIC follows mapped fire hazard areas. The national WUI census layer does not adopt that code. Oregon R327 follows local adoption. Colorado CWRC Chapter 3 is an AHJ overlay with low, moderate, or high fire intensity. The WUI map does not adopt those books.
3. Do not treat it as Cohen. The 2.4 km interface buffer is an estimate of how far a firebrand can fly ahead of a front. Cohen’s 2000 paper puts ignition on the house and about 40 meters. Distant firebrands still need a landing pad. See home ignitability.
4. Housing density is the floor, not the risk. 6.17 units per km² is one house per 40 acres. Seasonal homes count. Vacant units count. That is census, not a roof class.
5. Fire risk is a different layer. Radeloff. Fuel, weather, and the house are not in that definition. Premiums can move with no nearby fire for the same reason. A model is not this map.
Washoe County makes the distinction operational. Its official EZ Fire-WUI map
returns a parcel hazard category, but the applicable fire district still has
to determine water and defensible-space conformity before Table 503.1 produces
IR1, IR2, or IR3. One map color is an input, not the finished construction
answer. See the Washoe County place record.
What people mix up
“In the WUI” as a burn sentence.
National WUI as FHSZ or as CWRC fire-intensity class.
2.4 km as Zone 2.
9 percent of land as 9 percent of Oregon lots under R327.
Screenshotting a 2005 journal figure onto this site. Draw in FA tokens after G3, or do not draw.
How to check
Open Treesearch 14912. Find intermix. Find interface. Find 6.17. Find 2.4 km.
Walk 40 meters from the walls. That is Cohen, not Radeloff.
If a carrier or planner says “WUI,” ask which definition. Federal Register census, FHSZ, or something else.
Do not take 2005 housing counts as a 2026 inventory.
Limits
This page does not remap the United States. It does not update 2005 counts. The 2018 growth paper was not opened here. FireApproved is not the Forest Service. Confirm the map the official is actually using.
The Where this differs asides each report one jurisdiction’s own mapping instrument, in that jurisdiction’s words. This site does not classify a parcel and does not read yours: the adopted map, and the official reading it, decide where a lot sits.
Is the USFS WUI map the same as a CAL FIRE FHSZ map?
No. Radeloff 2005 applies a Federal Register housing-and-vegetation definition to census blocks and land cover. A Fire Hazard Severity Zone map is a California construction overlay. You can sit in the national WUI and outside a Very High FHSZ, or the reverse relative to local construction rules. See how to read a CAL FIRE FHSZ map.
Does WUI mean the house will burn?
Radeloff says the Federal Register definition does not explicitly account for differences in fire risk. Cohen 2000 says ignition depends on the house and about 40 meters, not on a landscape WUI polygon. Homes in the mapped WUI can have low ignitability. Homes outside it can still take firebrands.
What is intermix versus interface?
Intermix is houses mixed into wildland vegetation, above 6.17 housing units per km² and at least 50 percent wildland vegetation in that census block. Interface is developed land above that housing density, with less than 50 percent wildland vegetation, within 2.4 km of a heavily vegetated area larger than 5 km². The 2.4 km is an estimate of firebrand flight, not Cohen’s 40-meter home-ignitability neighborhood.
Does Oregon R327 follow this map?
No. R327 applies where a city or county adopted it. The national WUI map does not adopt code. California CWUIC follows mapped fire hazard areas, not the 2005 national WUI census layer. Colorado CWRC Chapter 3 is a local construction overlay with fire-intensity classes, not Radeloff.
Does Washoe County's parcel hazard result finish the construction answer?
No. The official EZ Fire-WUI map returns the parcel hazard category. The applicable fire district must separately confirm water and defensible-space conformity before Table 503.1 yields IR1, IR2, or IR3. The map result alone is not a roof or vent specification.
Does Pennsylvania's statewide 2021 IWUIC adoption assign my parcel's construction class?
No. 34 Pa. Code § 403.21 incorporates the 2021 IWUIC statewide, but that adoption alone does not locate a parcel on an official WUI map or assign Class 1 construction. This site keeps the official-map, assigned-class, project, and building-official checks open.