Fire-Resistant Green Building
The following is an excerpt from When Technology Fails: A Manual for Self-Reliance, Sustainability, and Surviving the Long Emergency by Matthew Stein. It has been adapted for the Web.
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 the 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. 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.
If current scientific predictions of global warming prove anywhere near correct, then the horrific 2007 fires outside of San Diego and the 1993 Laguna Beach fires are simply a preview of future wildfires that will endanger hundreds of thousands of homes 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, there are a number of actions you can take to improve the chances that your home will survive a local wildfire.
Lessons from the 1993 Laguna Fire
- Many (if not most) homes in this fire 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, and so on. 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 firewall 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.
- Defensible space: One of the few Laguna homes in the path of the firestorm to survive had a 40- foot-wide strip of the green succulent called “ice plant” and a concrete-tiled 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 5/8-inch sheetrock firewall for improved fire resistance. Cement-based weatherboard (Hardie Board, Certainteed, etc.) can look like wood but give you cement board’s superior fire resistance. Even with a stucco or cement weatherboard 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 (preferably), or natural wood may be painted with a coating to improve its fire resistance. Hot air rises and can easily ignite roof overhangs in a firestorm.
- Decks: 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). 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 has a new Class B fire-resistant-rated recyled plastic-and-wood composite decking, and other manufacturers are coming out with similar products.
- Roofs: 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 due to the fire down below.
(Adapted from “Fire-Resistant Details: Studying the Houses That Survived the 1993 Laguna Beach Fire Storm Yields Lessons in Building to Withstand the Heat,” by John Underwood, Fine Home Building.com)
My fireman friends tell me that when they enter a neighborhood, they take mental notes about which homes have maintained a defensible space and which have not. They don’t waste their time focusing on homes without a defensible space, but spend their time defending homes where they stand a decent chance of success, while keeping a watchful eye on nearby flames. These are brave guys, risking their necks where most of us would not go, but they have wives and kids––so when a vicious firestorm gets dangerously close, they simply have to leave the neighborhood and let nature take its course.
Green and Fire Resistant
There are a number of “green building” systems that are inherently fire resistant. Basically, if a system 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. The following is a partial list of fire-resistant green building modes of construction:
- SCIP (Structural Concrete Insulated Panel): The concrete skins, high insulation, and thermal mass of SCIP walls make this form of building extremely fire resistant, especially if you make the roof out of SCIPs too.
- Cob: The high thermal mass of thick, earth-based cob walls are also extremely fire resistant.
- ICF (Insulated Concrete Forms): The concrete and steel structural heart of ICF walls is fireproof, but the foam and exterior wall sheathing of some ICFs may not hold up well under fire even though their high thermal mass and insulation should prevent internal ignition. Some ICFs, like the Durisol system, are inherently fireproof, but other systems, especially if they are sheeted with wood siding instead of cement board or stucco, could be severely damaged or burned in a fire.
- Adobe: Another high-mass, earth-based system that is inherently fire resistant. Pay attention to the above suggestions pertaining to roofs, venting, and windows.
- Rammed Earth/PISE: High-mass, earth-based systems are inherently fire resistant. Pay attention to the above suggestions pertaining to roofs, venting, and windows. PISE is a system developed by David Easton for seismic zones to replace rammed earth with shotcreted soil cements that are heavily reinforced with structural steel rebar.
- Straw Bale: When covered with stucco, earthen, or lime based plasters, straw bale walls have been shown to be extremely fire resistant. When encapsulated, it is extremely difficult to get a straw bale to ignite. Some straws, such as rice straw, have a high silica content that makes them naturally fire resistant.
- SIP (Structural Insulated Panels): When sheathed with cement board siding, SIPs have a fire resistance that is far superior to traditional stick framed walls, but not as good as the earth or cement based systems.
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