Southern Californians have to realize that sooner or later all chaparral must burn. If you build near chaparral you must either be prepared to lose your house or else design it to protect itself on the assumption that firefighters cannot defend it.
As homeowners begin to rebuild after our recent wildfires, there are a few simple architectural design decisions that will greatly improve the chances their new home will survive the next wildfire.
The key to survival is to understand the way a wildfire attacks a house. The building code is primarily designed to protect your house from a fire that starts indoors from something like a cigarette or short circuit, grows slowly and may eventually reach the building's structure. A wildfire attacks from the exterior. Driven by strong winds, it reaches peak temperatures in seconds and may pass over your house and be gone within minutes, once all the standing fuel is consumed. If you design your new home to withstand this massive but brief horizontal attack, it has a good chance of survival.
Locate your home to get as much distance and incombustible material as possible between you and the chaparral, using patios, driveways and low-growing fire-retardant plants. You might be attacked from any direction, but an up-slope running fire is the most dangerous and so deserves special design attention.
First, you need an incombustible exterior. Tile, stucco, adobe, concrete block or metal can be used to create a beautiful home. It is essential to enclose the underside of roof overhangs, balconies and under-floor areas where flames will be trapped and temperatures will be the highest. Decks and handrails must be incombustible. The most insidious problems are the cracks and openings in Spanish tile roofs where the wind can drive sparks and embers inside your attic, so choose roof tiles that interlock tightly and are installed over incombustible paneling.
Windows are the weakest link in defending your building, but there are clever ways to protect them. Radiant heat alone from the fire can shatter glass and ignite combustibles inside your living room, without the flames actually reaching your house. Double-pane glass with low-emissivity coatings will help, as long as the window is not left open. The surest solution is rolling metal fire doors recessed into the roof overhangs or side panels.
Wood doors can withstand the initial fire attack but can support flames after the firestorm has passed. Garage doors are especially vulnerable, so consider a metal panel door with an automatic fusible link closure. It must fit tightly because if the wind drives a burning ember under the door all is lost.
Large vents in the attics and under-floors can be protected by automatic fire dampers. Check that all bathroom, dryer and kitchen vents have metal sleeves and automatic, fire-rated back-draft dampers.
Once the firestorm passes over, spot fires might remain, so consider a heat-activated roof and patio sprinkler system. Design your house so that exterior lights and aluminum ladders you set up to the roof will be visible from the street to encourage the firefighters to choose your house to defend.
A home built using these simple precautions not only has a better chance of surviving a firestorm but provides much greater safety for the people who live in it and the firefighters trying to protect it.