Washington Administrative Code › Title 51 - Enterprise Services, Department of (Building Code Council) › Chapter 51-55 - State Building Code adoption and amendment of the 2021 edition of the Wildland-Urban Interface Code › Section 51-55-0300 - Wildland-urban interface areas

Current through Register Vol. 24-14, July 15, 2024
301 General.
301.1
Scope.
Wildland urban
			 interface areas shall be determined using the Washington wildland urban
			 interface map (WA-WUI). WA-WUI designations are permitted to be modified, upon
			 approval of a finding of fact in accordance with Section 302.
User note:
The WA-WUI map is available at
https://geo.wa.gov/maps/786aaa1dbbd748e6ae04bc43c8f127fe/explore
.
301.2
Construction in
			 wildland-urban interface or intermix areas.
Where a structure is proposed to be constructed in an area
				designated by the WA-WUI map as wildland-urban interface or intermix, the
				construction shall comply with the provisions of this code.
301.3
Construction in wildlands
			 areas.
Where a structure is proposed to be constructed in an area
			 designated by the WA-WUI map as wild-lands, the applicable wildland urban
			 interface area designation shall be based on a finding of fact in accordance
			 with Section 302.
302 Wildland-urban interface area
				designations.
302.1
General.
Wildland urban interface area designations are permitted
			 to be established in accordance with this section.
302.2
Finding of fact.
The
			 applicable wildland urban interface designation shall be based on a finding of
			 fact. The finding of fact shall comply with the provisions of Appendix E or is
			 permitted to be based on the worksheet and procedures in Section
			 302.3.
302.3
Simplified
			 wildland urban interface designation worksheet.
The wildland urban
			 interface designation is permitted to be established using the procedure
			 outlined in Table 302(1), using the worksheet in Table 302(2).
302.3.1
Area to be evaluated.
For the purposes of establishing structure and vegetation densities, the area
			 covered by a square of 1320 feet on a side (40 acres) shall be evaluated. The
			 square area shall be located such that the site under consideration is in its
			 center, except where the square would overlap a water body shown on the WA-WUI
			 map with a surface area greater than 200,000 square feet, the location shall be
			 adjusted such that no part of the square overlaps the water body.
Table 302.3(1)
Outline of Simplified Procedure for Determining Wildland
				Interface Designation
For the area to be evaluated in
						  Section 302.3.1:
1. Determine structure density category (uninhabited,
						  very low, low, medium, or high).
2. Determine vegetation density category (nonvegetated
						  or vegetated).
3. Determine proximity category (near or
						  distant).
4. Based on structure density, vegetation density, and
						  proximity categories, determine if compliance with this code is
5. Where compliance with this code is required,
						  determine wildland urban interface area designation (intermix or
302.3.2
Structure density
			 category.
The structure density category shall be determined by counting
			 the number of structures within the area to be evaluated per Section 302.3.1.
			 The structure density category shall be determined as follows:
UNINHABITED:
0 structures
VERY LOW:
1 structure
LOW:
2 to 8 structures
MEDIUM:
9 to 120 structures
HIGH:
more than 120 structures
302.3.3
Vegetation density
			 category.
Vegetation coverage within the area to be evaluated per
			 Section 302.3.1 shall be determined in accordance with Chapter 9. Vegetation
			 density shall be determined by dividing the vegetation coverage by 1,742,400
			 square feet (40 acres). Where the vegetation density is less than 50 percent,
			 the vegetation density category for the site shall be nonvegetated. Where the
			 vegetation density is 50 percent or more, the vegetation density category for
			 the site shall be vegetated.
302.3.4
Proximity category.
The
			 distance from the site being evaluated to a high-density vegetated area shall
			 be measured from the closest edge of the site boundary to the closest edge of
			 the nearest high-density vegetated area. Where the distance is less than 1.5
			 miles, the proximity category shall be near. Where the distance is 1.5 miles or
			 more, the proximity category shall be distant.
302.3.5
WUIC applicability.
The
			 WUIC shall apply, and the site shall be designated as intermix or interface in
			 accordance with Section 302.3.6 under either of the following conditions:
1. The structure density category is very low
			 to high, and the vegetation density category is vegetated.
2. The structure density category is very low
			 to high, and the proximity category is near.
The WUIC shall not apply under either of the following
				conditions:
1. The
			 structure density category is uninhabited, and the site is not located within
			 an area designated as intermix or interface on the WA-WUI map.
2. The structure density category is
			 uninhabited to high, the vegetation density category is nonvegetated, and the
			 proximity category is distant.
302.3.6
Wildland urban interface area
			 designation.
Where required by Section 302.3.5, the site shall be
			 designated as intermix or interface in accordance with Section 302.3.6.1 or
			 302.3.6.2.
302.3.6.1
Intermix
			 designation.
The site shall be designated as intermix where the
			 structure density category is very low to high, and the vegetation density
			 category is vegetated.
302.3.6.2
Interface designation.
The site shall be designated as interface
			 where the structure density category is very low to high, and the proximity
			 category is near.
Table 302(1). Outline of simplified procedure for
				determining wildland interface designation
1. Determine structure density category in
			 accordance with Section 302.3.2. Numbers in table are the number of structures
UNINHABITED
VERY LOW
LOW
MEDIUM
HIGH
0
1
2 to 8
9 to 120
MORE THAN 120
2.
			 Determine vegetation density category within the area determined by Section
			 302.3.1.
NONVEGETATED
VEGETATED
Less than 50% vegetated
50% or more vegetated
3.
			 Determine proximity category to the nearest high-density vegetated area.
NEAR
DISTANT
Less than 1.5 mi (2.414 km)
1.5 mi (2.414 km) or more
4. Use
			 structure density, vegetation density, and proximity categories from above to
			 determine if WUIC applies.
WUIC
						  Applies
WUIC Does Not
						  Apply
* Structure density category is very low to high;
						  and
* Structure density category is uninhabited;
						  and
* Vegetation density category is
						  vegetated.
* The site is not located within an area designated as
						  intermix or interface on the WA-WUI map.
* Structure density category is very low to high;
						  and
* Structure density category is uninhabited to high;
						  and
* Proximity category is near.
* Vegetation density category is nonvegetated;
						  and
* Proximity category is distant.
5.
			 Where WUIC applies, the site shall be designated as intermix or interface as
			 follows:
INTERMIX
INTERFACE
* Structure density category is very low to high;
						  and
* Structure density category is uninhabited;
						  and
*Vegetation density category is
						  vegetated.
Proximity category is near.