Wildfires and fires occurring in Wildland-Urban Interface (WUI) areas have seemingly become more common, even in areas outside of those traditionally considered as prone to wildfires. Recent years have also seen an increase in research efforts regarding wildfires and how the built environment reacts when exposed to wildfire. These efforts continue to inform the development of testing methods, design & construction practices, and building codes to help mitigate, or at least manage, wildfire risk in the built environment. This article explores the key building codes that govern design and construction in wildfire-prone and WUI areas, with a particular focus on how combustible materials can be used in compliance with these codes.
Codes Governing Wildland-Urban Interface (WUI) Areas
The most well-known building codes for materials, design, and construction methods in wildfire and WUI areas are:
- Chapter 7A of the California Building Code1
- Section R337 of the California Residential Code2
- The International Wildland Urban Interface Code (IWUIC)3
These codes take a similar approach to regulating building design and construction in areas designated by the local Authority Having Jurisdiction (AHJ) as Wildland-Urban Interface (WUI) areas or areas with a wildfire hazard.
Key concepts common to these codes include managing vegetation; resistance to ignition (from flame, heat, and flying embers) and fire resistance of the building; and various topics related to fire-service response and operations such as area fire protection plans, fire service access, and water supply.
As with all building codes, the requirements layer and build upon other provisions within the respective building code along with its scope, administration, and application.
Combustible Materials in WUI Areas
Although one might assume that wildland-urban interface code “WUI code” requirements would discourage, if not prohibit, the use of combustible building materials, that is not the case.
When designed, constructed, and installed in accordance with applicable code provisions, combustible materials remain viable options for use in buildings within WUI areas or areas subject to increased wildfire risk.
Put simply: “WUI does not mean everything must be noncombustible.”
WUI ≠ Noncombustible
This fact is of particular importance in the context of the building envelope (i.e., exterior wall assemblies and roof assemblies) and building materials such as combustible exterior wall coverings and claddings, water-resistive barriers, foam plastic insulations, and roof coverings.
Both California codes and the IWUIC requirements include multiple prescriptive and performance-based compliance options.
Code Compliance for Combustible Building Materials
Two examples are provided below to illustrate how combustible building envelopes can comply with “WUI codes.” These examples do not represent requirements for comprehensive code compliance. Designers and code users are responsible for determining specific requirements and compliance for any specific project or application.
Example 1: Roof assemblies – IWUIC and California Building Code, Chapter 7A
The IWUIC requires that roof assemblies comply with either Class A or Class B fire classification, depending on which Ignition-resistant Construction Class (Class 1, 2, or 3) is required. The California Building Code, Chapter 7A also requires all roof assemblies in these areas meet Class A fire classification. The roof assembly fire classification is obtained based on testing in accordance with ASTM E1084 or UL 7905. (See the IWUIC and California Building Code for further information.)
Both ASTM E108 and UL 790 are assembly tests that evaluate the fire performance of a roof covering installed over a roof deck in response to an exterior fire exposure. Roof assemblies containing combustible materials that provide Class A or Class B performance meet the IWUIC requirement.
Example 2: Exterior wall assemblies – California Building Code, Chapter 7A
The California Building Code, Chapter 7A, includes separate requirements for exterior wall coverings and exterior wall assemblies.
– Exterior wall coverings:
Exterior wall coverings are required to comply with one or more of three (3) compliance options, unless the entire exterior wall assembly meets the requirements for exterior wall assemblies. The options require that the exterior wall covering shall be one of the following:
- Noncombustible material
- Ignition-resistant material (based on tests for extended-duration surface burning characteristics)
- Fire-retardant-treated wood
– Exterior wall assemblies:
Exterior wall assemblies are required to comply with one or more of seven (7) compliance options, unless the exterior wall covering complies with the exterior wall covering requirements above. The options for exterior wall assemblies contain several assembly fire tests and prescriptive design options that include:
- Assembly that has been tested in accordance with the 10-minute direct flame contact exposure test of ASTM E27076 with the conditions of acceptance shown in [California Building Code] Section 707A.4.1.
- An assembly that meets the performance criteria in accordance with the test procedures for a 10-minute direct flame contact exposure test set forth in SFM Standard 12-7A-17.
- An assembly that provides a 1-hour fire-resistance rating, rated from the exterior side, when tested in accordance with ASTM E1198 or UL 2639.
- An assembly containing one layer of 5/8-inch (15.9 mm) Type X gypsum sheathing applied behind the exterior wall covering or cladding on the exterior side of the framing.
Assemblies containing combustible materials that meet any of the assembly fire performance tests or prescriptive design options above meet the California Building Code, Chapter 7A, requirement.
A Performance-Based Path Forward for Wildfire Resilience
NAMBA advocates for a balanced, performance-based approach to wildfire resilience – one that embraces innovation and recognizes the proven safety of modern combustible building materials when used in compliance with established codes and standards.
We remain committed to supporting research, education, and code development that enhances fire safety while preserving material choice and design flexibility.
Footnotes
- International Code Council, Inc. 2022 California Building Code: California Code of Regulations, Title 24, Part 2. International Code Council, Inc., Washington, DC. 2022. ↩︎
- International Code Council, Inc. 2022 California Residential Code: California Code of Regulations, Title 24, Part 2.5. International Code Council, Inc., Washington, DC. 2022. ↩︎
- International Code Council, Inc. 2024 International Wildland Urban Interface Code [IWUIC]. International Code Council, Inc., Washington, DC. 2023. ↩︎
- ASTM E108 Standard Test Methods for Fire Tests of Roof Coverings ↩︎
- UL 790 Standard Test Methods for Fire Tests of Roof Coverings ↩︎
- ASTM E2707 Standard Test Method for Determining Fire Penetration of Exterior Wall Assemblies Using a Direct Flame Impingement Exposure ↩︎
- SFM Standard 12-7A-1 Exterior Wall Siding and Sheathing ↩︎
- ASTM E119 Standard Test Methods for Fire Tests of Building Construction and Materials ↩︎
- UL 263 Fire Tests of Building Construction and Materials ↩︎
