- Remove flammable materials from around the building. Current codes require that homeowners clear flammable vegetation within 30 feet of buildings and modify vegetation within 100 feet around buildings to create a “defensible space” for firefighters to safely protect their homes.
- Construct the building of fire resistant material, using methods that resist burning embers intrusion, the main cause of home loss during Wildland-Urban Interface (WUI) fires.
The flame spread rating of a material is determined by subjecting material placed in a horizontal “Steiner” flame spread tunnel to a gas flame. The material is attached to the upper surface of the tunnel and is rated on the distance the flame travels down the length of the tunnel, on the exposed surface of the material. The duration of this test is 10 minutes. A combustible material will be rated as Class A, Class B or Class C based on its performance in this test.
The heat release rate can be determined by measuring the mass (weight) loss of a burning material or by measuring the total and/or rate of energy released while a material is burning. The heat release rates have been published for common construction materials and are one of the criteria some materials must meet to comply with Chapter 7A of the California Building Code. Chapter 7A provides the requirements for new construction in California’s designated wildfire prone areas.
This code chapter establishes minimum standards for the protection of life and property by increasing the ability of a new building located in any California Fire Hazard Severity Zone within State Responsibility Areas, any Local Agency Very-High Fire Hazard Severity Zone or any other designated Wildland-Urban Interface Fire Area to resist the intrusion of flames and to protect buildings from being ignited by flying embers which can travel as much as a mile away from the wildfire. It is a touchstone for similar codes in other states.
Windows in particular are considered to be one of the most vulnerable components of a structure when it is exposed to fire. This vulnerability is due to several factors. The thermal shock of direct exposure to flames or the impact of airborne debris could shatter the glass, permitting burning brands or flames to enter the building, virtually assuring its destruction. Conventional wisdom holds that the window frame is also susceptible to burn-through under direct flame exposure. It has been theorized that radiant or convective heating, such as from adjacent burning shrubbery, might not break the glass but could ignite or deform the window frame, allowing the glass to fall out and again exposing the building interior to flames.
However, testing conducted in 2002 at the University of California Forest Products Laboratory concluded that all window products failed when subjected to high heat levels and the performance is dictated by glass type, rather than by window type or the specific framing material. This testing was a key factor in mitigating early knee-jerk code reactions that threatened a wholesale ban of vinyl windows.
Exterior Windows – SFM Standard 12 TA-2
There are several ignition-resistant standards referenced in the California regulations that are designed to prevent embers from igniting a building. The one applicable to windows is CA (State Fire Marshal) SFM 12.7A-2, Exterior Windows, which sets forth testing methodology and acceptance criteria for windows exposed to direct flames
The standard describes acceptable windows as “insulating-glass units with a minimum of one tempered pane, or glass block units or have a fire resistance rating of not less than 20 minutes, when tested according to referenced test methods.
The 2009 Supplement to 7A references NFPA 257, Standard on Fire Test for Window and Glass Block Assemblies, in place of the originally cited ASTM 2010, Standard Test Method for Positive Pressure Fire Tests of Window Assemblies, which has been withdrawn by ASTM. NFPA 257 prescribes standardized fire and hose stream test procedures that apply to the evaluation of fire window assemblies, including windows, glass blockand other light-transmitting assemblies intended to retard the spread of fire through openings in fire resistance–rated walls. Exterior windows, window walls, glazed doors and glazed openings within exterior doors must be insulating-glass units with a minimum of one tempered pane, or glass block units, or have a fire-resistance rating of not less than 20 minutes, when tested according to the referenced method.
The test method requires fabrication of a test module—a prefabricated 4’ x 8’ wall section containing the test window, which may be of any type or size that fits within the wall. Install the window according to the manufacturer’s guidelines. Any type of framing material may be tested.
A propane diffusion burner with the required heat output is placed against the wall assembly until flame-through occurs at the window at the glass or in the frame. At that point, the burner is extinguished and the window is monitor for sustained combustion. The time elapsed and location of penetration, if it occurs, is noted. To pass the test, the window assembly must withstand eight minutes of direct flame exposure with the absence of flame penetration through the window frame or pane, or structural failure of the frame or pane.
Doors are required to conform to the performance requirements of standard SFM 12-7A-1 or must be of approved noncombustible construction or solid core wood having stiles and rails not less than 1 ⅜” thick with interior field panel thickness no less than 1 ¼” thick, or have a fire resistance rating of not less than 20 minutes when tested according the referenced test method. The 2009 supplement referenced NFPA 252, Standard Methods of Fire Tests of Door Assemblies in place of the originally cited ASTM 2074, Standard Test Method for Fire Tests of Door Assemblies, Including Positive Pressure Testing of Side-Hinged and Pivoted Swinging Door Assemblies, which has also been withdrawn.
All conformance testing must be performed by a testing agency approved by the State Fire Marshal or identified by an ICC or ICBO Evaluation Service report.
Approved Products Handbook/BML
In an effort to provide homeowners, contractors, designers and local fire and building officials with a list of compliant WUI products, the California Department of Forestry and Fire Protection’s (CAL-FIRE) State Fire Marshal's Office publishes a “WUI Products Handbook” under its Building Materials Listing (BML) Program. All products listed in this handbook, which is posted on the Office of the State Fire Marshal’s BML website, have been reviewed and verified for compliance with the WUI codes. Each product approval and listing is based upon an evaluation of test results.
The State Fire Marshal's BML program lists materials that meet the new code. These materials will be listed on the Office of the State Fire Marshal’s BML website and the Wildland-Urban Interface Building Codes page of the Wildland Hazards and Building Codes website section. The SFM listing service provides building authorities, architectural and engineering communities, contractors and the fire service with a reliable and readily available source of information.
A majority of the WUI approved products, at manufacturers’ requests, have been transitioned into the BML program. They are listed under several categories, including 8120‐Exterior Windows and 8150‐Exterior Doors.