Wildland Urban Interface Code Guide
Wildland Urban Interface Code (WUI) Guide:
Building Construction Requirements
INTRODUCTION
Wildland firefighting by itself is very challenging and adding structures and other improvements into the equation greatly increases the complexity. Over the last several decades an expansion of communities, homes and other improvements into wildland areas has created a significant challenge for the fire service agencies responsible for providing fire protection in those areas.
Winds during wildfires carry huge amounts of burning embers, swirling into cracks and crevices, igniting anything that is easily combustible. Eaves tend to capture blowing embers because they are perpendicular to the wall. Eave vents, which are designed to move air in and out of the attic, give opportunity for embers to ignite soffit material or enter attic areas. Once a fire starts in an attic, it goes undetected for some time and is very difficult to stop even under ideal conditions.
Washoe County has adopted the International Wildland Urban Interface Codes sicne 2013 and is currently operating under the 2024 International Wildland Urban Interface Code. The purpose of this guide is to provide an overview of the building construction requirements of the new Wildland Urban Interface (WUI) Code requirements, summarize the County’s interpretations and approvals, identify changes over the previous edition, and to provide references for those seeking further information.
WUI CODE REQUIREMENTS
Washoe County has adopted chapter 5 of the WUI code which identifies the Ignition Rating based on the applicable Fire Hazard Severity and Fire Protection District's determination of defensible space and water conformity per Chapter 6 of the WUI code which has been adopted by each Fire Protective District.
Fire Hazard Severity -
Fire Hazard Severity is classified as one of the following:
| Low | Moderate | High | Extreme |
| Blue | Green | Orange | Red |
To determine the Fire Category of a property:
- Click EZ Fire-WUI Map
- Enter the property Address or Assessor Parcel Number in the upper right hand corner.
- The associated color determines the property designated Fire Risk Rating Category.
Defensible Space & Water Comformity -
- Water Comformity is determined based on if your property falls within 1000 ft distance of a fire hydrant.
(Driving on a road as a fire truck travels, not as a bird fly's) - Required Defensible Space is determined based fire hazard severity and the fuel modification distance.
|
Low
|
Moderate
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High
|
Extreme
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N/A
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30 ft
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50 ft
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100 ft
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Contact the associated local Fire Protection District for that property.
| Email Contact | Phone Contact | |
| Truckee Meadows Fire Protection District (T.M.F.P.D) | FirePrevention@TMFPD.us | 775-326-6079 |
| North Lake Tahoe Fire Protection District (N.L.T.F.P.D) | 775-831-0351 |
Ignition Rating Determination -
The Ignition Rating for each property is determined based on fire hazard and water and defensible space conformity determination; which should be confirmed by the applicable Fire District.
Once the Fire Hazard and Water and Defensible Conformity has been verified, then the Ignition Rating for the property can be determined by utilizing the following table:
| TABLE 503.1 IGNITION-RESISTANT CONSTRUCTION | ||||||
| Fire Hazard Severity | ||||||
|
Defensible Space (Chapter 6) |
Moderate Hazard | High Hazard | Extreme Hazard | |||
| Water Supply | Water Supply | Water Supply | ||||
| Conforming | Nonconforming | Conforming | Nonconforming | Conforming | Nonconforming | |
| Nonconforming | IR 2 | IR 1 | IR 1 | IR 1 NC | IR 1 NC | Not Permitted |
| Conforming | IR 3 | IR 2 | IR 2 | IR 1 | IR 1 | IR 1 NC |
| 1.5 Conforming | Not Required | IR 3 | IR 3 | IR 2 | IR 2 | IR 1 |
| Note: IR 1 NC shall have exterior walls of 1 hour fire resistive construction and exterior siding material shall be noncombustible. | ||||||
Ignition-Resistant Construction Requirements based on Ignition Resistance Rating Determination:
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IGNITION-RESISTANT CONSTRUCTION
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|||
| 2024 IWUIC 504 |
2024 IWUC 505 |
2024 IWUIC 506 |
|
| Roofs |
· Class A |
· Class A |
· Class B |
| Eaves |
· IR material |
· Enclosed with solid material (3/4” min.) |
|
| Fascia |
· IR material |
· Enclosed with solid material (3/4” min.) | |
| Ventsb,c |
· <144 square inches |
· <144 square inches |
· <144 square inches |
| Exterior Walls |
· Approved 1-hour FRCd |
· Approved 1-hour FRCd |
|
| Windows |
· Tempered glass |
· Tempered glass |
|
| Doorse |
· Approved noncombustible construction |
· Approved noncombustible construction |
|
| Appendages (i.e. Decks)f |
· 1-hour FRC |
· 1-hour FRC |
|
| Unclosed Underfloor |
· Enclosed to ground |
· Enclosed to ground |
· Enclosed to ground |
| Gutters & | · Noncombustible material | · Noncombustible material | · Noncombustible material |
| Downspouts | · Prevent accumulation of leaves and debris | · Prevent accumulation of leaves and debris | · Prevent accumulation of leaves and debris |
| a. When provided. | |||
| b. Gable end, soffit, eave, and dormer vents shall be located at least 10 feet (3048 mm) from lot lines. | |||
| c. Attic ventilation openings at soffits, eaves, or overhang areas must be approved devices only. | |||
| d. On the exterior side. | |||
| e. Exception: Vehicle access door. | |||
| f. See WUI Code, amendments, and guide for additional restrictions or exceptions. | |||
WUI BUILDING CONSTRUCTION REQUIREMENTS
Roofs: Roofs assemblies shall be the appropriate class (A, B, or C) for the ignition construction class. When provided, valley flashing shall be not less than No. 26 galvanized sheet gage. Any space between the roof covering and roof decking or at the eave end shall be fire stopped to prevent the entry of flame or embers.
- IWUIC 507.1 - The roof covering on buildings or structures in existence prior to the adoption of this code that are replaced or have 25 percent or more replaced in a 12-month period shall be replaced with a roof covering required for new construction based on the type of ignition-resistant construction specified in accordance with Section 503.
Roof Gutters: Roof gutters and downspouts shall be constructed of noncombustible materials. Gutters shall be provided with an approved means to prevent the accumulation of leaves and debris.
Eaves & Fascia: Eaves, fascia, and soffits shall be protected on the exposed underside by approved 1 hour fire resistant construction (FRC), ignition-resistant (IR) material, 2x lumber, fire retardant treated wood labeled for exterior use. No exposed tails unless heavy timber (6x8). Other architectural trim boards are exempt.
Vents: Each vent shall not exceed 144 square inches in area and shall be covered with noncombustible corrosion-resistant mesh with openings not to exceed 1/8 inch or shall be designed and approved to prevent flame or ember penetration into the structure. Vents in soffits, eaves, or overhangs areas shall be an approved venting device only. Attic ventilation vents shall be located at least 10 feet from lot lines.
Exterior Walls: Exterior walls surfaces shall be either an approved 1 hour fire resistant construction (FRC), approved noncombustible material, heavy timber or log wall construction, fire retardant treated wood labeled for exterior use or ignition-resistant (IR) material. Architectural trim boards are exempt. Approved 1-hour FRC shall mean any 1-hour fire rated assembly or any exterior siding when installed over one layer of 5/8” Type X exterior gypsum sheathing that is tightly butted or taped and mudded.
- Examples of acceptable wall materials are stucco, masonry, cement-fiber board, and other materials meeting the testing requirements for noncombustible (ASTM E136) or ignition-resistant (ASTM E 84 or UL 723) materials with a minimum Class A flame spread rating.
- IR 1 NC shall have exterior walls of 1 hour fire resistive construction and exterior siding material shall be noncombustible.
Windows (Glazing): Exterior windows, window walls, glazed doors, glazed opening within exterior doors, and skylights shall be either tempered glass, insulating (dual or tripled glazed) glass units, glass block, or have a minimum 20 minute fire resistive rating. It is recommended that in addition vinyl windows shall have a label certified meeting ANSI/AAMA/NWWDA 101/I.S.2-97 structural requirements. Otherwise, window frames, sashes, and screens have no WUI requirements.
Exterior Doors: Exterior doors shall be either approved noncombustible construction, minimum 1 ¾” solid core, or have a fire protection rating of not less than 20 minutes. Door frames have no WUI requirements. Vehicle access doors are exempt. Door thresholds, frames, screens, and weather stripping have no WUI requirements.
Patio Covers, Trellis’ & Carports: Patio Covers, trellis’, carports and other roof projections and attachments shall be an approved 1 hour fire resistant construction (FRC), approved noncombustible material, heavy timber construction, fire retardant treated wood labeled for exterior use or ignitionresistant (IR) material.
- Heavy Timber Construction. As defined in Chapter 2 of the NLTFPD 2024 Amendments to the International Wildland Urban Interface Code. For decks and similar structures:
- Minimum 6x6 columns
- 4x8 joists
- 4x10 or 6x8 beams
- 3x ledgers
Decks & Balconies: Decks and Balconies shall be an approved 1 hour fire resistant construction (FRC), approved noncombustible material, heavy timber construction, fire retardant treated wood labeled for exterior use or ignition-resistant (IR) material. Underfloor areas shall be enclosed within 6” of the ground when any portion projects over a descending slope greater than 10%, unless the under floor area is free from storage or vegetation.
- Heavy Timber Construction. As defined in Chapter 2 of the NLTFPD 2024 Amendments to the International Wildland Urban Interface Code. For decks and similar structures:
- Minimum 6x6 columns
- 4x8 joists
- 4x10 or 6x8 beams
- 3x ledgers
- 2x decking
- Only decking surfaces of decks with defensible space and under floor area free from storage and vegetation shall comply with the WUI code material requirements or the third party approved decking material.
- Decking material must have a flame spread index less than or equal to 25 when tested with the extended ASTM E84 or ASTM E2768 tests to have a Class A rating.
- There are no fire resistive requirements for handrails, guards, and balusters.
- Coated materials shall not be used as the walking surface of decks
Fences and Other Attachments: Any portion of a fence or other structure within five feet of the building shall be constructed of noncombustible material or material that meets the same fire resistive standards as the exterior walls.
2024 International Existing Building Code
I.E.B.C. 703.1: Alterations shall be done in a manner that maintains the level of fire protection provided.
I.E.B.C 1101.1: An addition to a building or structure shall comply with the International Codes as adopted for new construction without requiring the existing building or structure to comply with any requirements of those codes or these provisions.