Chapter 7A predominately addresses the deck surface (deck boards, rails, treads, etc.), not the underlying structural support members. (i.e., the part of the deck you can walk on). It doesn't require enclosing the deck.
Chapter 7A assumes that you have created an acceptable defensible space around your home or building. This includes the area under the deck. The under-deck area shown in this photograph would not comply with the intended 'defensible space' requirements of the new building code.
There are three ways decking can comply with the requirements of Chapter 7A. The first is a performance-based method that relies on passing both parts of California Office of the State Fire Marshal standard SFM 12-7A-4 (i.e., Parts A and B). Part A is an under-deck flame impingement exposure. Part B is conducted by placing a large (Class A) burning brand on top of the deck. Decking complying via this option must also be classified as an ignition resistant material.
Parts A and B (the first option) have seven conditions of acceptance, as shown below.
Part A, Under deck test:
- Peak heat release rate of less than or equal to 25 kW/ft2.
- Absence of sustained flaming or glowing combustion of any kind at the conclusion of the 40-minute observation period.
- Absence of structural failure of any deck board.
- Absence of falling particles that are still burning when reaching the burner for floor.
Part B, Burning Brand Exposure:
- Absence of sustained flaming or glowing combustion of any kind at the conclusion of the 40-minute observation period.
- Absence of structural failure of any deck board.
- Absence of falling particles that are still burning when reaching the burner of floor.
This slide shows dropping debris (left) and structural failure (right). All seven conditions of acceptance must be met to comply via this option.
A definition of an ignition resistant material has been adopted and used in Chapter 7A. The definition is based on the test standard UBC 8-1 (ASTM E-84), and utilizes the Steiner Tunnel shown in this photograph. The result of this test is a flame spread rating. The term 'ignition resistant' is given to materials that obtain a flame spread rating of 25 or less when subjected to an extended (30 minute) test. Materials must also be subjected to an accelerated weathering procedure set forth in UBC 23-4 (ASTM D-2898), and meet the same flame spread requirement ( 
This photograph shows a 12"x12" 'A' brand, 6"x6" 'B' brand, and small 'C' brand. The 'A' and 'B' brands consist of ¾-inch Douglas-fir sticks that are nailed together in a three-layer sandwich construction. The middle layer is perpendicular to the top and bottom layers.
The second method includes a few options, including 1) heavy timber construction (as specified in Section 605.6 in the California Building Code), 2) deck boards that are exterior-rated fire retardant treated lumber (this product meets the definition of an ignition resistant material) or 3) approved noncombustible material (such as metal deck boards or a light weight concrete surface, as shown in this slide). For decking and stair treads, 'heavy timber' means that deck boards are a minimum of 3-inches thick.
Here is an example of a deck with a 'heavy timber' structural support system. Chapter 7A does not require this kind of construction, although timbers this size are harder to ignite.
The third option is a variation on the first option, but is less restrictive. The decking only needs to meet the minimum heat release rate requirement of Part A (i.e., the HRR can't exceed 25 kW / ft2 of deck area). The remaining three criteria for Part A don't apply (self-extinguish, dropping flaming debris, and structural failure). Conducting the brand test (Part B) also isn't required.
Products that comply using this option should also provide flame spread information (either Class A, B, or C). If you can't find it, assume Class C. If the flame spread is Class C, then exterior siding within 10-ft of the deck must be either noncombustible or ignition resistant (untreated wood siding, vinyl siding, other combustible siding cannot be used). If the flame spread is either Class A or B, then siding that complies with any of the provisions of Chapter 7A can be used.
Most deck boards comply via this option.
San Diego County has a different requirement for decking. It is more restrictive than the third option and less restrictive than the first option. A summary of the San Diego County requirement is given below.
Part A. Under-deck flame impingement exposure.
- Acceptance criteria:
- HRR
- Glowing allowed after 40 minutes (no flaming)
- Cannot drop flaming debris
- Cannot break under own load
Part B. Brand test (top of deck) - Use of 'B' brand instead of 'A' brand allowed.
- Acceptance criteria:
- Glowing allowed after 40 minutes (no flaming)
- Cannot drop flaming debris
- Cannot break under own load
Since currently the state doesn't require marking the edge of the deck boards to show compliance and San Diego County does, markings similar to the ones shown in this slide will mean that the product complies in San Diego County.
These are examples of various types of wood (or other fiber) plastic composite (WPCs) materials.
Tests conducted at the UCFPL Fire Research Laboratory indicated that boards with channeled construction didn't perform as well when subjected to an under deck flame impingement exposure. Boards with a hollow construction didn't perform as well when exposed to the ('A') brand (on top of deck) test. Engineering and formulation changes that many manufacturers are doing to comply to SFM 12-7A-4 may change this general rule.
For a current list of deck products that comply to Chapter 7A provisions, go the California State Fire Marshal's wildfire and hazards web page and click on 'New Products Handbook'.
When viewing decking information in the WUI Products Handbook (or other location), be sure to note how the product complied. If by Option 3, then make note of the flame spread rating – it will be either Class A, B, or C. If the flame spread rating is Class C, then the adjacent siding will have to be either non-combustible (a fiber cement siding product, stucco, etc.), or ignition resistant (such as exterior fire retardant treated wood). Most decking products comply via the third option.
The WUI Products Handbook is published on-line by the Office of the State Fire Marshal as a pdf document. It is updated regularly.
A fee must be paid to OSFM to have a product included in this handbook. Manufacturers are not required to include their compliant products in this, or any, publication. However, this is an easy way to show compliance. Manufacturers wishing to have their product included in this book must have their product tested at an OSFM approved fire laboratory. The test report, prepared by the fire laboratory, must be submitted to OSFM for review and approval.
As part of a fire demonstration, a burning 'B' brand was placed on both of these decks. This photograph was taken approximately 60 minutes after the burning brands were placed on the decks. The decking product on the left does not comply with the provisions of Chapter 7A. The decking product on the right does comply. Since Chapter 7A only applies to new construction (those buildings constructed since January 2008) and not to new decks built on older homes, both of these products are commercially available.
