Home hardening and defensible space are the two main strategies used to protect your home from wildfire. While defensible space addresses the vegetation around the structure – home hardening addresses the structure itself – and “hardens” it against the heat and embers of a wildfire. Most people understand the need to protect a home from flames, but it’s important to remember that high severity wildfires can send embers miles ahead, igniting homes well ahead of the flames.
Wildfires may seem like a concern only for mountain communities, but the 1991 Oakland Hills Firestorm is a good reminder that even suburban neighborhoods can be at risk. The standards for building in high fire severity zones are spelled out in Section 337 of the 2022 California Residential Code and in Chapter 7A of the 2022 California Building Code.
Wood roofs were once common, but they can easily ignited by falling embers. Current standards require Class A rated roofing materials, such as asphalt composition shingles or metal roofing (with a Class A underlayment). Metal valley flashings require the installation of cap sheet roofing below the metal flashing, to prevent heat from being transferred through the flashing. Gutters are required to have gutter guards installed to prevent an accumulation of debris in the gutter, as you want burning gutter debris to be above the level of the roof sheathing. Edge flashing, which covers the gaps between the roofing and gutter, are also a critical component that protect the roof sheathing from burning.
Building codes require venting of crawl spaces and attics, but screens with oversized openings can allow embers to pass through – as well as allow the passage of intense radiant energy. Therefore, all vents are required to be a flame and ember resistant type that prevent both the entry of embers and also the radiant energy. The screen openings need to be ⅛ inch or smaller (not the typical ¼ inch spacing) to prevent ember entry, and some type of special coating or mechanical closing device is needed to block radiant energy. Radiant energy is what you feel when sitting too close to a campfire, and blocking radiant energy is especially important when buildings are closer than 30 feet apart (e.g. Berkeley and Oakland hills). Plastic venting materials often used for ridge venting are not appropriate, as the plastic will melt. Vulcan is a popular vent manufacturer.
Exterior Siding & Trim
Siding materials can make a big difference in the survivability of a building. For obvious reasons, all types of wood siding should be avoided. The most fire resistant siding is traditional 3-coat stucco, which is luckily a prevalent siding type on older homes in the Bay Area. Another good siding option is fiber cement, such as HardiePlank. Open eaves are discouraged, as the exposed roof framing can catch fire, and it’s better to soffit the roof overhang with either stucco or fiber cement materials. Trim boards should also be made from fire resistant materials.
Doors, Windows, & Glazing
Traditional wood doors and windows (fenestration) are not the best option, and it’s best to have fenestration with metal cladding and a solid wood frame. Some vinyl and fiberglass windows have an internal metal frame that can keep them from deforming in a fire, but others do not, so it’s important to make sure all fenestration has a 20-minute fire rating (NFPA 257 or CA State Fire Marshal Standard 12-7A-2).
Glazing is required to have at least two panes (double paned), and have at least one pane of tempered glass, as tempered glass is much more heat resistant than regular glass. The code does not specify which pane should be tempered, but it makes the most sense to position the tempered pane on the exterior, and for just a modest increase in price, you can use tempered glass for both panes. Skylights are also required to be tempered, and operable skylights need to be protected by a non-combustible mesh screen with openings ⅛ inch or less, to prevent ember entry should a skylight be left open.
Garage doors shall resist the intrusion of embers by limiting gaps on all sides to ⅛ inch or less, as well as having a 20-minute fire rating.
Wood decks are basically a giant campfire waiting for an ember, however there are ways to reduce their flammability and potential damage to the house. A metal flashing at the deck to wall intersection, is required to run up the wall vertically at least 6 inches, which will give the building greater protection in an area where combustible debris can accumulate. The decking material is required to be non-combustible or ignition resistant. Metal is non-combustible, but it can get quite hot on sunny days, and therefore composite decking and dense tropical hardwoods are often used. There are no special requirements for the deck framing, although enclosing the deck framing with fiber cement skirting is a good idea.
- Fire in California (University of California)
- Hardening Your Home (CalFire)
- Harden Your Home (Fire Safe Marin)
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