Building homes to defend against the next wildfire
By Brian Torone, Torone Consulting
The rebirth of neighborhoods in Kenwood and many other areas of Sonoma and Napa counties has just begun. With it, thousands of new homes will be built, hopefully in short order. The resilience of many of our Kenwood neighbors and the speed at which they are already moving to create their new homes has been impressive. Thus, this is the perfect time to learn from past wildfires and consider better ways to design and construct new homes to achieve a high level of fire resistance.
Below is a summary of the most significant preventative measures that can be taken as put forth by architects, firefighters and industry experts. Many of these measures can also be taken by homeowners to upgrade the fire resistance of their existing homes.
House structureThe most effective structures for fire-resistant houses are poured concrete, concrete block, and brick, because those materials do not ignite and there is little or no air within the walls of the structure. The next most effective is steel because it can be fireproofed in a number of ways.
Unfortunately, the most common structure is wood stick framing, which happens to provide the exact elements required to escalate a fire - kindling and air pockets between framing members. Thus, if wood framing is to be used, it is essential that the home's exterior envelope provide the maximum possible fire protection.
Exterior siding In the wildfires, embers were shot through the air by high winds, directly igniting structures. They also created fires by landing on fences and shrubs beside houses, ultimately igniting them. Stucco and fiber-cement exteriors are two of the most fire resistant siding materials. Stucco is excellent at resisting ignition and its smooth finish does not catch flying embers. Fiber-cement siding (such as “Hardie plank”) has also performed well in fire testing, although its performance appears to be highly dependent on the installation configuration of the boards. Other good siding options, although more rarely used in California, are stone, brick, exposed concrete and concrete block. In our wildfire environment, wood plank, wood batten siding and vinyl siding are not recommended.
Roofing The most inexpensive type of roof is composite (or asphalt) roofing. Some new asphalt roofing products have greater fire resistance than that of decades past. However, much more fire-resistant materials include metal roofing, slate, tile, or concrete roof tiles, all of which have excellent fire ratings.
Cedar shake roofs are not recommended, and can accelerate a fire.
Decking Most wood species used for decks do not resist fire very well, and many just add fuel to an already raging fire. If wood must be used for an exterior deck, then using fire-retardant treated lumber is one option. Another is to apply a fire retardant wood sealer. There are two good alternatives to wood: construct the deck from fire resistant wood composite materials, or cover the deck with tile or stone.
Windows Double-pane windows are insulated and are much more effective than single-pane against breaking in the heat of a fire. Tempered glass is also more effective at resisting heat than regular plate glass. Since sliding doors are generally made of tempered glass, they are a good option for fire protection if large panes are desired. Wood, wood clad with aluminum, and fiberglass window frames have done well in flame tests, and are better than vinyl, which has the possibility of melting in extreme heat. Acrylic skylights tend to melt and allow fire penetration.
Eaves and vents The main problem with overhangs in a wildfire is that since flames rise, burning materials next to the house can catch the eaves and/or roof rafters on fire, and the house can burn from the top down. One defense against this is to use stucco or fiber-cement board to box in the eaves and rafters. Another option, though somewhat less effective, is to paint the underside of the eaves with a fire resistant paint.
Foundation and roof venting that is specially made for fire resistance is available. In any case, vents should always be covered with screen to prevent embers from entering the house. Fine screen is better and should have openings that are 1/8-inch maximum.
Walls and fencing Concrete block, poured concrete or stucco walls are the best wall option between properties to stop the spread of fire. Modular concrete or cementitious walls are also available.
In the Kenwood [Nuns] fire, untreated wood fences caught fire, provided fuel, and spread the fire from property to property. Wood fences are generally much less expensive than masonry or stucco. So if wood fences are used, they should be treated with fire retardant paint or coatings. Since these coatings lose their effectiveness over time, however, they need to be retreated every two to five years.
Vinyl fences do not perform well under the intense heat and flame of wildfires.
ConclusionEvery homeowner is faced with unique challenges in rebuilding or remodeling. However, whatever the challenges, significant steps can be taken to reduce or eliminate damage from wildfires. These steps may also slow the spread of fire and provide our firefighters with additional opportunities to save homes in the future.
Brian Torone is an architect who lives in Kenwood.