CRC R337.9.3: WUI Deck Walking Surface Fire Requirements
Understanding California's fire performance requirements for deck walking surfaces in Wildland-Urban Interface zones, the 7 compliance options, and how classified roof covering systems fit in.
What is R337.9.3?
Section R337.9.3 of the California Residential Code (CRC Chapter 7A) sets fire performance requirements for the walking surfaces of decks, porches, balconies, and stairs in Wildland-Urban Interface (WUI) zones. It applies when the deck surface is within 10 feet of the building.
Chapter 7A exists to protect buildings from wildfire exposure. The deck walking surface requirements address two fire scenarios: fire approaching from below the deck (such as burning vegetation or stored materials) and fire exposure from above (such as wind-blown embers landing on the deck surface).
When R337.9.3 Applies
- The project is in a designated WUI zone (also called a fire hazard severity zone)
- The walking surface is within 10 feet of the building
- The surface is part of a deck, porch, balcony, or stairway
- The local jurisdiction enforces CRC Chapter 7A requirements
The 7 Compliance Options
R337.9.3 provides seven ways to demonstrate that a deck walking surface meets WUI fire performance requirements. Each option references specific test standards or material types:
Item 1: ASTM E2632 + ASTM E2726
Deck assembly passes both the under-deck fire exposure test (E2632) and the burning brand test on the walking surface (E2726).
Item 2: SFM 12-7A-4 (Parts A and B)
Deck assembly passes the California State Fire Marshal's two-part test: under-deck fire exposure (Part A) and burning brand on the surface (Part B).
Item 3: ASTM E2632 + SFM 12-7A-4 Part B
Combination approach using the ASTM under-deck test with the SFM burning brand test.
Item 4: SFM 12-7A-4A + ASTM E2726
Uses the SFM alternate under-deck test with the ASTM burning brand test.
Item 5: Ignition-resistant materials
Walking surface made of approved ignition-resistant materials as defined by CRC Section R337.2.
Item 6: Noncombustible materials
Walking surface made of noncombustible materials (concrete, masonry, steel, etc.).
Item 7: Classified roof covering assembly
Walking surface that is part of a classified roof covering assembly tested per ASTM E108. This is the compliance path for walking deck and roof covering systems evaluated under ICC-ES AC39.
Understanding the Fire Testing Standards
R337.9.3 references several fire test standards. Here's what each one measures:
ASTM E2632 — Under-Deck Fire Exposure
Tests how a deck assembly responds to fire approaching from below. Simulates fire from burning vegetation, stored materials, or debris beneath an elevated deck. Does not evaluate above-surface fire exposure.
ASTM E2726 — Burning Brand on Deck Surface
Tests the deck surface response to a 12" x 12" burning brand (simulating wind-blown embers) placed on top of the walking surface. Note: ASTM withdrew E2726 in 2026 without replacement. R337.9.3 still references it, but check with your building official about accepted alternatives.
SFM 12-7A-4 — California State Fire Marshal Deck Test
A two-part test developed by the California State Fire Marshal specifically for deck assemblies in WUI zones:
- Part A: Under-deck fire exposure (similar to ASTM E2632)
- Part B: Burning brand on the walking surface (similar to ASTM E2726)
SFM 12-7A-4A — Alternate Under-Deck Test
An alternate version of the SFM under-deck fire exposure test. Used in combination with ASTM E2726 under Item 4.
ASTM E84 / ASTM E2768 — Surface Burning Characteristics
Measures flame spread and smoke development of surface materials in a 25-foot tunnel test. ASTM E2768 is an alternate method using a smaller sample. These tests determine Class A vs Class B fire ratings. While not directly referenced in R337.9.3 compliance options, these ratings are part of the overall fire evaluation for classified roof covering systems.
ASTM E108 — Roof Covering Fire Classification
The most comprehensive above-surface fire test for roof coverings. ASTM E108 Class A testing evaluates:
- Spread of flame: How flame travels across the roof surface under wind
- Intermittent flame: Cycled flame application simulating wind-driven fire conditions
- Burning brand: A 12" x 12" burning brand placed on the surface (the same brand size used in E2726 and SFM 12-7A-4 Part B)
- Flying brand: Smaller burning embers carried by wind across the surface
ASTM E108 is the basis for roof covering classifications (Class A, B, or C) and is the test referenced by R337.9.3 Item 7 for classified roof covering assemblies.
Fire Test Comparison
This table shows what fire exposures each test standard evaluates:
| Fire Exposure | E2632 | E2726 | SFM 12-7A-4 | E108 Class A |
|---|---|---|---|---|
| Under-deck fire | Yes | No | Part A | No |
| Burning brand (above) | No | Yes | Part B | Yes |
| Spread of flame | No | No | No | Yes |
| Intermittent flame | No | No | No | Yes |
| Flying brand | No | No | No | Yes |
ASTM E108 Class A is the most comprehensive above-surface fire test, covering all four fire exposures that roof coverings may face. The WUI-specific tests (E2632, E2726, SFM 12-7A-4) each address specific fire scenarios but do not test for spread of flame, intermittent flame, or flying brand exposure.
Classified Roof Covering Systems vs Composite Deck Boards
This is the most common point of confusion in R337.9.3 plan review. Plan checkers who are accustomed to reviewing composite deck boards may not recognize that classified roof covering systems are a fundamentally different product category.
Composite Deck Boards
- Evaluation: ICC-ES AC174
- Product type: Individual lumber-like boards
- Fire testing: Typically ASTM E84 for surface burning; may also test per E2632/E2726 for WUI
- Function: Walking surface only (not a roof covering)
- Common R337.9.3 path: Items 1-4 (deck-specific fire tests)
Classified Roof Covering Systems
- Evaluation: ICC-ES AC39
- Product type: Complete multi-layer system (substrate + membrane + coatings)
- Fire testing: ASTM E108 (roof covering classification) + ASTM E84 (surface burning)
- Function: Walking surface and roof covering
- R337.9.3 path: Item 7 (classified roof covering assembly)
Why this matters for plan review
When a plan checker sees a "deck" product in a WUI zone, they may default to requesting the deck-specific fire tests (ASTM E2632, E2726, SFM 12-7A-4) because those are the tests they associate with deck walking surfaces.
However, a classified roof covering system evaluated under ICC-ES AC39 is not a "deck board" product. It's a complete roof covering system that has already been fire-tested per ASTM E108 — which includes the same 12" x 12" burning brand exposure used in E2726 and SFM 12-7A-4 Part B, plus additional fire exposures (spread of flame, intermittent flame, flying brand) that the WUI-specific deck tests do not cover.
Navigating Plan Check Corrections
If you receive a plan check correction requesting ASTM E2632, E2726, or SFM 12-7A-4 test reports for a classified roof covering system, here's how to respond:
Documentation to Provide
- ICC-ES Evaluation Report: The ESR confirms the product is evaluated as a roof covering system under AC39, not as composite decking under AC174
- AC39 Scope of Evaluation: Reference the sections showing the product is a "walking deck and roof covering system"
- ASTM E108 Fire Test Data: Show the Class A roof covering classification, which includes burning brand, spread of flame, intermittent flame, and flying brand exposures
- R337.9.3 Item 7 Reference: Cite the specific code section that provides a compliance path for classified roof covering assemblies
If the Plan Checker Requires Further Discussion
Building officials have the authority to accept alternative means of compliance. If the initial response doesn't resolve the correction:
- Request a meeting with the plan checker to walk through the compliance documentation
- Bring the ESR report, AC39 evaluation criteria, and ASTM E108 test data
- Explain the distinction between composite deck boards (AC174) and classified roof covering systems (AC39)
- Reference R337.9.3 Item 7 as the applicable compliance path
- Contact the product manufacturer's technical team for additional support documentation
Frequently Asked Questions
What is CRC R337.9.3?
CRC R337.9.3 is a section of the California Residential Code (Chapter 7A) that specifies fire performance requirements for walking surfaces of decks, porches, balconies, and stairs within Wildland-Urban Interface (WUI) zones. It applies when these surfaces are within 10 feet of a building and requires compliance through one of seven listed options involving specific fire test standards or materials.
Does ASTM E108 Class A testing satisfy R337.9.3 requirements?
Yes. R337.9.3 Item 7 allows walking surfaces that are part of a classified roof covering assembly. ASTM E108 Class A testing is the most comprehensive above-surface fire test available, including spread of flame, intermittent flame, flying brand, and burning brand exposures. A walking deck system evaluated as a classified roof covering under ICC-ES AC39 and tested per ASTM E108 satisfies R337.9.3 through this compliance path.
What is the difference between composite deck boards and classified roof covering systems?
Composite deck boards are individual lumber-like products evaluated under ICC-ES AC174 for use as decking material. Classified roof covering systems (evaluated under ICC-ES AC39) are complete multi-layer assemblies that serve as both a walking surface and a roof covering. These are fundamentally different product categories with different evaluation criteria, fire testing, and code compliance pathways. Plan checkers accustomed to reviewing composite deck boards may not recognize this distinction.
What fire tests does ASTM E2632 cover?
ASTM E2632 tests deck assemblies for fire exposure from below (under-deck fire). It evaluates how the deck system responds when fire approaches from underneath, such as from stored materials or vegetation beneath an elevated deck. This test does not evaluate above-surface fire exposure like burning brands or flame spread across the walking surface.
Has ASTM E2726 been withdrawn?
Yes. ASTM E2726 (the test method for burning brand exposure on deck surfaces) was withdrawn by ASTM in 2026 without replacement. However, R337.9.3 still references E2726 in some compliance options. Building officials may accept alternative tests that cover the same fire exposure, such as the burning brand portion of SFM 12-7A-4 Part B or the burning brand test within ASTM E108. Consult your local building official for guidance on acceptable alternatives.
How do I respond to a plan check correction citing R337.9.3?
If a plan checker requests ASTM E2632, E2726, or SFM 12-7A-4 testing for a classified roof covering system, provide the ICC-ES evaluation report (ESR), the AC39 evaluation basis showing the system was evaluated as a roof covering, and the ASTM E108 fire test data. Explain that the product is a classified roof covering system (not a composite deck board) and that R337.9.3 Item 7 provides a compliance path for classified roof covering assemblies. If needed, request a meeting with the plan checker to discuss the alternative compliance path.
Related Resources
Fire Ratings Explained: Class A vs Class B
Understand ASTM E84 fire testing and what Class A and Class B ratings mean
Understanding ICC-ES AC39
Learn about the acceptance criteria for walking deck and roof covering systems
California SB 721/SB 326 Compliance
Balcony inspection laws and code-compliant waterproofing for California properties
ICC-ES ESR-3672 Report
Full evaluation report for Deck Flex walking deck and roof covering systems
Technical Specifications
Full CSI specifications for both fire-rated systems
Fire Suppression Standards Reference
Comprehensive reference on fire suppression standards for building materials
Working on a Project in a California WUI Zone?
Our technical team can help with project-specific compliance documentation, plan check response letters, and guidance on R337.9.3 compliance pathways for classified roof covering systems.