Beyond the Defensible Space: Fire Safety and the Structure of Your Home, by Matthew Stein

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Given the record breaking droughts, heat waves, and fire storms of the summer of 2012, if current scientific predictions of global warming prove anywhere near correct, then the we can expect that this scary situation will become the new normal  in the coming years. Whether you are a homeowner wishing to improve the fire resistance of your current dwelling, or are planning to build a new home, beyond creating a “defensible space” around your home there are a number of other actions you can take to improve the chances that your home will survive a local wildfire. These guidelines are typically applied to homes located in areas where long periods of dry weather are common, such as many of the western states. However, due to changing times people in many areas where the threat of wildfires was previously a non-issue are now finding it to be a growing concern.

Lessons from the 1993 Laguna Fire

In October 1993, when a vicious wildfire broke out in Laguna Beach, a southern California beach town, firefighter John Henderson was called down from his home in the Sierras of northern California to fight this blaze. The combination of extremely dangerous fire conditions, brought on by three consecutive drought years coupled with 60 to 70 mph hot and dry Santa Ana winds, quickly whipped the fire into an unstoppable conflagration, burning hundreds of homes to the ground! When John rounded a corner on the Pacific Coast Highway, just north of Laguna Beach, he saw a sight that he will never forget. He and his partner watched the firestorm rush down the dry hills toward the ocean. The heat of the firestorm was so intense that, even after blowing across four lanes of pavement, it was hot enough to ignite a mile-long stretch of wooden telephone poles on the ocean side of the road. From a distance, he said they looked like a string of matchsticks stuck in the sand, igniting one after the other until there were perhaps a hundred telephone poles burning at once.

• Many if not most homes burned from the inside out when firestorm heat radiated through closed windows and slipped inside through foundation and roof vents to ignite interior curtains, rugs, etc. Double-pane windows and heavily insulated walls will slow the rate of heat penetration into interior spaces.
• The only buildings to survive the Laguna Fire had insulated walls, double-pane windows, and blocked or minimized venting. A well-insulated, well-sealed building envelope, and high thermal mass, will slow interior heating and ignition.
• Minimize venting, and screen all vent openings to prevent flaming embers from entering vents. Removable fire-wall vent blocks should be placed in front of foundation and roof vents during periods of extreme fire danger to keep hot air from easily penetrating the building envelope.
• One of the few Laguna homes in the path of the firestorm to survive had a 40-foot-wide strip of the green succulent “ice plant” (creating an excellent “defensible space”) and a concrete tiled roof (an exceptionally fire resistant roof). The firestorm blew right over the top of the ice plant and the house, dropped burning embers on the concrete tile roof, roasted a 10-foot-wide swath of ice plant, but failed to ignite the building’s structure.
• Stucco, cement, or earthen walls are preferred. If wood siding is desired, it should be applied over a ?-inch sheetrock fire wall for improved fire resistance. Cement-based weather board can look like wood but give you cement board’s superior fire resistance. Even with a stucco or cement weather-board sheath, an underlying wood-framed wall might ignite if the firestorm gets hot enough.
• All projections (roof eaves, etc.) should be protected on the underside with cement stucco or cement board (like Certainteed or Hardie Board) that looks like wood. A less-preferred alternative is to paint natural wood with fire-resistant coating to improve its resistance to ignition by burning embers. Hot air rises and can easily ignite roof overhangs in a firestorm.
• Coat wood decks with multiple layers of a fire-resistant urethane deck covering (Pacific Polymers or similar) or treat wood decking with fire-resistant coatings (Fire Stop or similar).
            Note: Chemical treatments, such as Fire Stop, will inhibit ignition by burning embers, but will not prevent ignition due to a super hot firestorm. A stucco coat (¾ inch or thicker) on the underside of wooden decks was credited with saving two homes in the Laguna Beach fire. There is a new fly-ash composite decking board from LifeTime Lumber that has a “Class A” fireproof rating, and is LEED certified for its recycled content, that can be used to build high-quality fireproof decks. Trex and many of the other similar competing composite decking manufacturers have come out with “Class B” fire-resistant wood/plastic composite decking to meet California’s new wildland fire codes.
• Use only “Class A” fire-rated roofing systems, which are rated to prevent both the roofing material itself, and roofing underlayment (plywood) from catching fire when covered with burning embers. Most asphalt and fiberglass shingles are Class A rated, but metal roofing usually requires the use of Versashield underlayment (or equal) to achieve this rating. “Living” roofs (planted sod) have excellent fire resistance as well as thermal mass and insulation. With Class A roofing, the eaves and overhangs are the most vulnerable areas of the roof owing to the fire down below. 
(Above list adapted and expanded from John Underwood, “Fire Resistant Details: Studying the Houses That Survived the 1993 Laguna Beach Fire Storm Yields Lessons in Building to Withstand the Heat,” Fine Home Building.com)
            There are a number of building systems that are inherently fire resistant. Basically, if it is earth or concrete based, it is very fire resistant. Also, if you fill the wall with foam or straw, to eliminate dead air spaces and the chimney effect, and sheath the wall with stucco, earthen plasters, or cement board, even if it is wood-framed it will have good fire resistance. Do your best to make your roof, eaves, and decks fire resistant too, since your home will only be as fire resistant as its weakest link. Obviously, traditional stone, brick, and concrete-block construction are also quite fire resistant, provided their roofs are not a weak link in the system.
            With burning embers settling on rooftops, in many cases it is the roof that forms the weak link in the fire-resistance chain. Traditional wooden shake and shingle are notorious for catching on fire from burning embers. For fire-resistant roofing, consider the following options:
• Use only “Class A” fire-rated roofing.
• Class A roofing must withstand burning embers on roof without igniting plywood sheeting.
• Most modern composition (asphalt) shingles are “Class A” fire-rated.
• Metal roofs transmit heat easily to the underlying plywood, so they tend to be not as fire resistant as you might imagine, unless they are underlaid with an insulating flame-resistant lining. They are usually only Class A fire resistant with the addition of Versashield underlayment (or similar).
• I recommend two layers of Versashield FR underlayment (or similar) FR barrier for extra fire barrier between metal roofing and its underlying plywood sheeting.

NOTE: This article was adapted from the author's book When Disaster Strikes: A Comprehensive Guide for Emergency Planning and Crisis Survival.

About the Author: Matthew Stein is SurvivalBlog's Back Country Editor. He is a design engineer, green builder, and author of two best selling books:When Technology Fails: A Manual for Self-Reliance, Sustainability, and Surviving the Long Emergency and When Disaster Strikes: A Comprehensive Guide for Emergency Planning and Crisis Survival.. Stein is a graduate of the Massachusetts Institute of Technology (MIT) where he majored in Mechanical Engineering. Stein has appeared on numerous radio and television programs and is a repeat guest on Fox News, Coast-to-Coast AM, Alex Jones’ Infowars, Vince Finelli’s USA Prepares, and The Power Hour.  He is an active mountain climber, serves as a guide and instructor for blind skiers, has written several articles on the subject of sustainable living, and is a guest columnist for the Huffington Post. His web sites are www.whentechfails.com and www.matstein.com

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This page contains a single entry by Jim Rawles published on August 13, 2012 2:46 AM.

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