The Next Fire: WUI Codes Could Help Lessen the Impact
While natural disaster newshounds watch alternating seasonal threats of East Coast hurricanes and West Coast wildfires like a tennis match, building codes have been shoring up the defenses in hopes of mitigating disasters such as 2005’s Katrina and 2007’s Witch Creek. We have devoted much discussion in these pages to the evolving codes and standards for hurricane wind, water and impact resistance, but have not revisited Wildland-Urban Interface (WUI) fire codes and standards for some time.
The next time Western wildfires kindle and threaten adjacent homes, they will hopefully meet a daunting challenge–at least from new buildings constructed under the latest California codes. Adopted in late 2005 by the California Building Commission, the Wildland Urban Interface Building Standard, Chapter 7A of the state building code, entitled Materials and Construction Methods for Exterior Wildfire Exposure, took effect in most jurisdictions January 1, 2008, for construction in designated wildfire hazard areas. The latter are geographical areas classified as very high, high, or moderate in state “responsibility areas” or as local agency “very high fire hazard severity zones.”
Patterned closely after the 2006 International Urban-Wildland Interface Code, the California state code addresses what state officials have identified as the two most common ways that buildings are lost during wildland fires: from direct exposure to heat and flames and from burning embers that can blow up to a mile ahead of the fire.
In the first regard, these 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.
The second component is to construct buildings that resist burning embers. Buildings catch fire when embers fall on wood roofs, blow into the building through vents, pile up in cracks or lodge under boards. Ignition-resistant construction creates an “envelope” around the structure to decrease the number of burning embers that can enter the building. By building the structure in a way that diminishes ember intrusion, the main cause of home loss during WUI fires can be reduced and even eliminated.
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 branches 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 that 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. As a case in point, the 2001 edition of the UWIC I-code contained the phrase “unapproved plastic or vinyl assemblies shall not be used,” which has since been removed. It is now recognized that vinyl products perform well under WUI hazard zone conditions when horizontal members are reinforced with an aluminum crosspiece.
The 2006 UWIC I-code requires windows used in high-risk areas to be “tempered glass, multilayered glazed panels, glass block or have a fire protection rating of not less than 20 minutes.” Exterior doors must be of “approved noncombustible construction, solid core wood not less than 1¾-inch thick,” or have a “fire protection rating of not less than 20 minutes.”
The 2007 California WUIBS uses essentially the same language in Section 704A.3-Exterior Walls, but 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 ASTM E 2010, or conform to the performance requirements of SFM 12-7A-2.” The latter, which sets forth testing methodology and acceptance criteria for windows exposed to direct flames, is one of several State Fire Marshal standards located in the California Referenced Standards Code, Part 12, Chapter 35 of the CBC. Note that the four stated requirements are not cumulative, but offer four compliance options.
Doors are required to “conform to the performance requirements of standard SFM 12-7A-1 or shall be of approved noncombustible construction, or solid core wood having stiles and rails not less than 13/8-inch thick with interior field panel thickness no less than 1¼-inch thick, or shall have a fire resistance rating of not less than 20 minutes when tested according to ASTM E 2074.”
The code requires conformance testing to be performed by a testing agency approved by the State Fire Marshal or identified by an ICC or ICBO Evaluation Service (ES) report.
A FIRE-RESISTANT SHOPPING LIST
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 is publishing a “WUI Products Handbook” under its Building Materials Listing (BML) Program. All products listed in this handbook have been reviewed and verified for compliance with the new WUI codes by the state fire marshal office staff. Manufacturers may submit applications for listings, and numerous roofing and siding products are already listed. The publishers note that the listings are voluntary and that materials not listed by the SFM may still qualify for use provided they meet all the requirements under Chapter 7A of the WUIBS.
As of the August 20, 2008, edition of the handbook, there are no window or door products listed. Manufacturers with products that qualify may want to have a look at this opportunity.
Meanwhile, numerous organizations are seeking to raise awareness throughout California and the West. For example, the International Code Council Foundation, the Federal Alliance for Safe Homes (FLASH) and The Home Depot Foundation are jointly sponsoring an educational campaign based on an instructive video, “A Tale of Two Houses—Wildfire.” Downloadable from www.flash.org, the video compares features of one home that survived the October 2007 Witch Creek Fire near San Diego with one that was destroyed. That fire torched 200,000 acres and 1,000 homes, but the flames bypassed the example survivor. Many states, as well as the Federal Emergency Management Administration, have also released publications addressing what homeowners should consider in protecting their WUI residence from potential fires.
It is gratifying to note that both the public awareness initiatives and the code provisions are working to dispel the myth that only “lucky” homes survive wildfires‚ showing that those built with specific preventative methods and materials can survive. It is also gratifying that the specific requirements have migrated from panic-induced and questionable panaceas to those based on science and well-conceived engineering. Just as with hurricane codes in the Southeast, AAMA and allied associations have had a role in this, and we will continue to contribute constructively wherever possible.