Ordinance Text

8-2-25: WILDLAND-URBAN INTERFACE (WUI) OVERLAY DISTRICT:

A. Purpose:

1. The Wildland-Urban Interface (WUI) Overlay District protects the public health, safety, and welfare by establishing standards to:

a. Minimize the potential of spreading fire from wildland areas to structures;

b. Establish special standards that apply to new construction, and the alteration, movement or change of use of habitable structures, with the intent to reduce the threat of loss of life and property from fire;

c. Require vehicle turnouts on new private roads with the intent to provide better emergency access to remote areas where needed; and

d. Require that new subdivisions and planned unit developments provide water supply systems and suitable access for firefighting crews, with the intent to increase the resources available to such crews and minimize the spread of fire.

2. Ada County has adopted the International Wildland-Urban Interface Code, (See Ada County Code Title 7, Chapter 2). This Section supplements that code with zoning and development standards.

B. Applicability:

1. Generally: These regulations apply to development as herein defined and as identified on the Wildland-Urban Interface overlay district map, the limits of which are adopted by Zoning Map (see Section 8-2-4) on file at the Ada County Development Services Department, or as amended.

2. Non-Habitable Structures: Non-habitable structures are exempt from these regulations, except when located within the defensible space as set forth in the regulations of subsection (C)(1) below.

3. Clearing: For purposes of this Section, the terms "clear," "cleared" or "clearing" means the removal of all vegetation except:

a. Single specimens of trees, ornamental vegetation, cultivated ground cover (such as green grass, ivy, succulents, or similar plants); and

b. Native grasses and weeds that do not readily transmit fire trimmed to a maximum height of four inches (4"). The Director may approve heights of 4- to 6-inches where needed to minimize erosion due to steep slopes.

4. Relocation: This Section does not require an owner to relocate existing habitable structures, driveways, or utilities.

5. Plant Species: In this Section, references to plant species that do not "form a means of readily transmitting fire" means:

a. The plant has a score of at least eight (8) for the applicable zone, as defined in the Fire Resistance of Plants Master Database and Placement of Species Within Firewise Landscape Zones for Southern Idaho developed by the Federal Bureau of Land Management, the College of Western Idaho Horticulture and the Idaho Botanical Garden and published by Idaho Firewise; or

b. The application demonstrates, and the Director finds, that the plant is fire resistant because it:

(1) Has a high moisture content in its leaves;

(2) Has little seasonal buildup of dead vegetation;

(3) Has a low, compact growth form;

(4) Is high in soap or pectin content;

(5) Has green stems; and

(6) Is drought tolerant.

6. Abutting Property: This Section does not require an owner to remove vegetation from an abutting property.

C. Vegetation Control Standards:

1. Defensible Space:

a. This subsection 1 applies to any "modification," defined as any new construction, or the alteration, movement or change of use of a habitable structure.

b. A modification requires a minimum fifty foot (50') defensible space around the perimeter of any habitable structure. Property owners shall maintain the defensible space unless that responsibility is transferred to another party through a binding contract. The defensible space shall meet the criteria in subsections c through j below.

c. Only single specimens of trees, ornamental vegetation, cultivated ground cover (such as green grass, ivy, succulents, or similar plants), or native grasses and weeds trimmed to a maximum height of four inches (4"), are allowed within the defensible space. Plants shall not form a means of readily transmitting fire. All other vegetation shall be removed from the defensible space. See Figure 8-2-25-1 below.

Figure 8-2-25-1 Defensible Space

d. All deadwood shall be removed from trees within the defensible space. Clusters or groups of trees shall be thinned so tree crowns do not overlap. Trees within the defensible space shall be pruned. Prune trees up to six feet (6') to ten feet (10') from the ground; for shorter trees do not exceed one-third (1/3) of the overall tree height. See Figure 8-2-25-2 below.

e. Tree crowns shall be pruned to maintain a minimum horizontal clearance of ten feet (10') from any structure or chimney outlet.

f. Liquefied petroleum gas containers shall not be located within the defensible space in accord with the applicable code as adopted by the state of Idaho.

g. Firewood and combustible material shall not be stored in unenclosed spaces beneath structures, on decks, or under eaves, canopies, or other projections or overhangs. All firewood and combustible material stored in the defensible space shall be located a minimum of twenty feet (20') from structures and separated from the crown of trees by a minimum horizontal distance of fifteen feet (15').

h. Agricultural structures are not allowed within the defensible space.

i. All accessory structures within the defensible space must meet the fire resistive construction standards for structures as established by the Ada County Building Code as set forth in Title 7, Chapter 2 of this code.

j. If an abutting public street or approved private road meets the standards for the defensible space as set forth above, the width of that roadway is counted as part of the defensible space.

2. Roads And Driveways: All areas adjacent to private roads and driveways shall be cleared of vegetation. Single specimens of trees, ornamental vegetation, cultivated ground cover (such as green grass, ivy, succulents, or similar plants), or native grasses and weeds trimmed to a maximum height of four inches (4"), are allowed, if these plants do not form a means of readily transmitting fire.

a. For driveways, all areas within five feet (5') of each side of the driveway shall be cleared.

b. For private roads, the area encompassed by the travel way plus five feet (5') on each side of the travel way, measured from the outside edge of the travel way, shall be cleared of all flammable vegetation.

3. Electrical Distribution And Transmission Lines: All vegetation shall be cleared from within thirty-one inches (31") of any above grade electrical distribution and transmission lines.

4. Electrical Conductors: All vegetation shall be cleared from within ten (10) radial feet of any non-insulated energized electrical conductor and associated live parts. Cultivated ground cover (such as green grass, ivy, succulents, or similar plants), or native grasses and weeds trimmed to a maximum height of four inches (4"), are allowed if these plants do not form a means of readily transmitting fire.

5. New Driveways/Construction Or Moving Structures: For new driveways, new construction, or moving of structures on a site, the areas that require vegetation removal shall be located within the property boundaries. The Director may approve a lesser standard if:

a. The property abuts a public or approved private road as set forth in subsection C1j of this Section; and/or

b. Severe topographic or other site constraints exist that prohibit locating new construction to meet the specified standard.

D. Private Road Standards:

1. All new private roads require vehicular turnouts for emergency vehicles. These turnouts require spacing at a maximum interval of seven hundred feet (700') with a minimum width of ten feet (10') and minimum length of thirty feet (30'). Road construction and vehicular turnarounds shall meet the private road standards as set forth in Section 8-3-11 of this Title. Driveways that meet turnout standards count as turnouts if they are at least twenty feet (20') wide and thirty feet (30') long.

2. Maintenance of the private road shall include vegetation control as specified in subsection C2b of this Section.

E. New Subdivisions And Planned Unit Developments:

1. An engineer, special expert (e.g., wildfire mitigation specialist), or other person that the Director finds has demonstrated competence and relevant wildfire experience, or training shall be retained who can demonstrate the following for the development:

a. Evaluate fire hazards and emergency access roads to determine site specific hazards and proper accessibility for emergency vehicles.

b. Prepare a fire protection plan that is specifically tailored to the proposed subdivision or planned unit development that includes:

(1) Completed fire hazard severity form from the current International Wildland-Urban Interface Code, appendix C, using nationally recognized standards;

(2) A fire protection plan map showing the roadway, turnouts, turnarounds, terminus, and lots;

(3) Determination of fuel model and fuel loading;

(4) Required signage for turnouts, turnarounds, and fire lane parking;

(5) Required number and placement of turnouts based on development density and roadway width;

(6) Requirements for fire resistance rated construction;

(7) Required road width or required interconnected system of roadways and fire accesses.

2. As part of the agency review process of subdivisions and planned unit developments, the fire protection plan shall be reviewed by:

a. The applicable fire district; or

b. If no fire district applies, the Ada County Sheriff, with advice from the Idaho State Fire Marshal.

F. Prohibited Uses: Campgrounds and seasonal farmworker housing are prohibited within the Wildland-Urban Interface overlay district.

(Ord. 1002, 10-28-2025)

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