Designing For Wildfires
The importance of neighbors, sustainability, and material selection
By Mark Johnson
Photos: Gabe Border
Year after year, wildfires have become a more important factor in our lives, and this impacts how we think about building design. The industry has always prioritized safety and endurance, but the size of the fires has prompted me to make choices that can help prevent or mitigate damage. These considerations—both material and immaterial—can help in planning for the possibility of fire to create smart, enduring spaces, for individual homeowners and for the community.
Site-Specific Design For Fire Zones
If a property is adjacent to wilderness, it’s important to limit dense vegetation, and to manage understory growth and forest floor debris year-round to foster a healthy forest base when fire season arrives. Neighboring properties will have a direct effect on a structure during a wildfire, so working with neighbors can make a real difference. For example, it’s important to separate fuel sources like propane, gas, or other flammables from the structure itself. The same goes for thoughtful landscaping that reduces ignitable ground surfaces, like drier, smaller bushes, around a home. Installation of rotary sprinklers, which are able to soak around a structure, will maintain a level of moisture unwelcoming to embers.
Some communities and counties in fire country find it helpful to foster partnerships—from neighbors and community groups to county and national agencies. Well-managed steps, informed by data, with clear instructions, can lead to a coordinated effort that serves the region. Understanding the ingredients for fire informs utilities, too, of the steps they can take to address the fire before it happens. These site-specific data are the keys in reducing the very ignition of a fire. Where utilities consider miles of terrain, neighbors can evaluate and act on their adjacent properties, and work through their neighborhood and community groups to engage in larger regional discussions.
Building Assembly
Once a site has been evaluated and prepared, designing a fire and heat-resistant building can actually borrow from sustainability approaches. Well-insulated walls and a roof and double- or triple-pane windows will maintain lower interior temperatures, reducing the chance of fire from inside the building. Air sealing—the method used in Passivhaus design—eliminates opportunities for embers to enter. Non-combustible siding reduces opportunities for embers to ignite the surface, and also reduces the chance for material to ignite due to heat from a nearby fire. Examples of especially resilient materials include metal siding, steel, concrete, stone, cement board panels, or fire-resistant, treated timbers like Shou Sugi Ban. Including a gypsum or plaster layer under the siding will increase the fire-resistive characteristics further. The same considerations apply to decks, shelters, and overhangs, where opting for fire-resistive materials with thoughtful detailing beneath will prevent a fire from carrying through to the structure. Fire-suppression mechanisms like sprinklers inside the building can reduce loss and prevent flames spreading if the building does ignite.
Site Selection
Understanding recent fire history, site conditions, fire utilities, and current forestry-management practices will help prioritize the prevention and mitigation strategies employed during design. If an adjacent area has recently burned, or has deployed forestry management or controlled burns, clear data and the level of local threats can be evaluated to determine the level of detailing. When locating a structure, incorporating local fire-management access and maintenance practices will reduce risk and allow firefighters to monitor the forest and control a fire when it occurs. Orienting decks, open space, and resilient materials with consideration of prevailing winds and detailing the openings in the structure, such as attic vents and siding gaps, will minimize opportunities for small embers to enter the structure. If a site has access to water, such as a creek, river, or lake, a pump and hose can be stored and periodically tested for immediate use against a fire.
Defensible Zones
The area around a building is a critical line of . This space can be categorized into three zones, each with best-practice recommendations from multiple local and national organizations. Observing guidelines and coordinating site planning and ongoing maintenance of the property with the local jurisdiction or fire department will enable fire response teams to know what to expect and provide the property owner with some control over the dynamic nature of fire.
Zone 1: Within 30 feet (10m) of the building. This is the area closest to the building; minimal vegetation should exist in this area, preferably limited to irrigated grasses. Driveways, patios, pavers, pools, and gravel are optimal surfaces. Potted plants that can be moved away from the structure in the event of a fire can create garden spaces. This zone should be swept clear of leaf litter, pine needles, and other vegetation debris by June 1 or prior to fire season, as directed by local jurisdictions or community organizations. No fuel tanks or wood storage should be located in this zone.
Zone 2: Within 30 to 60 feet (10m to 20m) of the building. Careful placement of shrubs and pruning and limbing of trees should be practiced. Wood storage and fuel tanks are permitted here, however, they should be located away from trees if possible. This zone should also be swept clear of vegetative debris prior to fire season.
Zone 3: All areas 60 feet (20m) or more from the structure. These areas can remain natural; however, regular maintenance to remove deadfall and standing dead trees, and managing extensive undergrowth will slow fire spread or ember ignition.
Wildfire is a dynamic threat to structures. While no structure can be considered fireproof, taking steps to understand the opportunity for file-fuel sources, fire personnel access, and surfaces around the building can create measurable results to reduce loss in the event of a wildfire. Resilience is critically important in fire zones—thinking beyond the property line to collaborate with neighbors and agencies to prepare for the worst can improve the outcomes when fire happens.
Mark Johnson, AIA, LEED AP BD+C, is a principal architect and founder of Signal Architecture + Research. Reach him at mjohnson@signalarch.com or visit www.signalarch.com.
Sources:
https://www.fs.usda.gov/nac/buffers/guidelines/5_protection/11.html
https://www.readyforwildfire.org/prepare-for-wildfire/get-ready/defensible-space/
https://www.fema.gov/media-library-data/20130726-1652-20490-9209/fema_p_737_fs_4.pdf