A home is only as fire resilient as its weakest link.
Minute design details can make the difference between a house that burns and one that doesn’t. There are numerous cost-effective strategies to reduce a home’s fire vulnerability while also reducing its resource use. These are important especially when considering the added costs of insuring a home without fire-resilient features. Such features span all stages of a design process. Many would be rendered impossible if rebuilders considered them late in the design process. Therefore, begin with massing (define home shape and form) and orientation that takes advantage of prevailing wind but addresses protruding elements that can trap embers near a home; design the envelope to minimize openings, and reinforce fire-vulnerable components like windows and vents; shade the building to improve passive cooling in the event of long-term power outages; and install systems to provide electricity and water in power outages. As evident by at least one recent study, fire resilient design can be accomplished for no added cost or construction time.
Content:
Design & Orientation
16. Build according to existing Wildland Urban Interface codes and above Title 24 2019 Building Energy Efficiency Standards.
Several building code standards can guide best practices for building in a wildfire urban interface (WUI) (see resources below). Building to WUI code compliance (resources #1, #2 & #3), increases the chances of a home surviving a fire, and will likely improve your chances of securing high-quality insurance at cheaper rates. With the right design and material choices, a new home built to WUI building codes can be constructed for around the same cost as a conventional home (see Headwater Economics’ report for a complete breakdown of building costs).
Designing to surpass Title 24 2019 energy code standards and installing solar PV (AB-178 exempts some rebuilders from installing solar) can also provide a net benefit for several reasons:
(1) it should make homes eligible for increased funding through Energy-Efficient Mortgages (EEMs) and SCE’s CLEAR program with up to $17,500 available to rebuilders with approved plans (see recommendation #10);
(2) on-site renewable energy generation mitigates the risk of rising electricity costs; and
(3) home improvements as a result of disaster rebuilding are exempt from capital value assessments as stipulated in CA Proposition 13 (see recommendation #13).
RESOURCES
NFPA 1144: Standard for Reducing Structure Ignition Hazards from Wildland Fire
CA Building Code Chapter 7A—Materials and Construction Methods for Exterior Wildfire Exposure
17. Reduce exposure to high winds by relocating building on site.
Rebuilders have some opportunity to move or reorient the new building without triggering an expanded permitting process. Consider if a nearby location on site is more clearly shielded from prevailing high winds or vegetation that may carry fire to the home. Keep in mind, airborne embers can accumulate near your home on the windward side (by getting trapped by protruding elements) and the leeward side (by way of low pressure eddies which pull airborne embers down to the ground).
ACTION
» Consult with a design professional to understand whether the new site location is feasible and advisable. Consider having a consultant run a wildfire simulation to determine better places to relocate the home on site (e.g. FlameMapper).
RESOURCES
For more information contact Shea Broussard at shea@flamemapper.com
18. To reduce vulnerability to wind-blown embers, minimize envelope (a building’s outer shell) openings and protrusions, screen all vents and locate them in easily accessible areas away from vegetation.
Wind-blown embers are the most frequent cause of a home ignition from wildfire. Embers often enter a house through open (unscreened) attic vents in the roof eaves, open crawl spaces, or HVAC intake/exhaust vents. Embers can also get trapped on or near a home as a result of the low-pressure wind eddies that protruding envelope details (e.g. parapets, chimneys, or overhangs) often create.
ACTION
» Start with slab-on-grade, basement, or sealed crawlspace to reduce openings underneath the building. Consider omitting vulnerable attic-space and instead designing roof and ceiling as one continuous module, unvented, and with exterior continuous insulation. For traditional vented roof assemblies, design gable-end vents (with fine metal mesh or manual closing mechanism) in place of ridge vents that run the length of the roof.
» Specify a centralized point-source inlet for the ventilation system. Locate vent openings at least 10 feet from adjacent buildings and vegetation. The location should also provide easy access for manually shutting the vent as part of a pre-evacuation checklist. Consider increasing the run (length) of inlet ducts to reduce likelihood of embers making it into the home. This can be done by running intake air through ducts in the crawlspace, or by using ‘Earth Tubes,’ to run intake air ducts underground allowing you to locate the intake vent further from a home.
» Use 1/8” metal wire mesh to screen all exhaust and inlet ducts and note that the ducts may need to be larger to mitigate the added pressure drop caused by the mesh. For more detail, see recommendation #31.
RESOURCES
19. Prioritize airtightness, continuous insulation, and low thermal bridging.
A key goal for both energy efficiency and fire resilience is low heat transfer through the building envelope. Creating a continuous air barrier with tightly sealed joints will reduce airborne (convective) heat transfer, while installing non- combustible continuous insulation (e.g. mineral wool) will reduce conductive heat transfer into and out of a building.
ACTION
» Include a continuous layer of rigid insulation between the foundation and the ground (recommend R-10, e.g. 3 inches of mineral wool). Design the wall-foundation and wall-roof connections to eliminate thermal bridging, which occurs when a conductive material such as a metal framing member passes through the otherwise continuous insulation layer. In addition to wall-cavity insulation, specify continuous 2 inch mineral wool insulation between the stud wall and the exterior siding or plaster (recommend total wall R-value 23). For roof insulation, aim for R-39 using cavity mineral wool insulation and 4 inches of continuous exterior mineral wool insulation.
» Airtightness is contingent on the continuity of the air barrier. An air barrier consists of materials that prevent air transfer (such as painted drywall or building sheathing) with all joints taped or sealed, including the joints at window and door openings, electrical outlets, plumbing connections, etc. Ideally the air barrier is tested with a blower door test before the walls are completely finished, so that any cracks can be sealed. Because prefab construction can be more tightly controlled, it can be a good way to produce airtight construction, if properly designed and executed. Some prefab companies guarantee a high level of airtightness (see recommendation #26).
20. Orient windows to maximize natural ventilation and design for passive cooling using high thermal mass flooring and wall materials.
Malibu’s climate is mild enough for the majority of a home’s cooling needs to be met with a well-designed passive cooling strategy. Two design considerations are needed for this energy-saving strategy: window placement and thermal mass. Proper window placement captures cross breezes and takes advantage of the thermodynamic properties of air to ensure continual fresh air circulation throughout the home. Indoor materials with high thermal mass (i.e. heightened ability to absorb and store heat) helps to stabilize indoor temperature swings, so you can retain nighttime temperatures for most of the day.
ACTION
» Take advantage of two key principles for natural ventilation:
(1) place windows across from each other in the path of prevailing winds; and
(2) place some windows at the highest point in a home to exhaust heat and pull cooler air in from the lower windows (stack effect).
» Use high thermal mass flooring or wall materials (e.g. stone, concrete, tile, thick gypsum wallboard) to slow heat building-up during the day. Pre-cool the thermal mass by ventilating at night (as described above), shut the windows as temperatures rise above about 70°F, and allow the thermal mass to soak up heat from the air to retain cool temperatures inside the home for most of the day.
» Keep in mind that windows in the path of prevailing wind are particularly at risk of compromise from wind-blown embers and heat. To address this, specify double-paned glass with fire-rated window components (see recommendation #25). For added security, install metal shutters that can come down in front of windows.
21. Minimize roof overhangs; use metal overhangs or louvers to control solar the sunlight (and accompanying heat) entering your home.
Overhangs and shading mechanisms are a key strategy for energy-efficient home design. However, if they are not properly designed, they can make your home more vulnerable to fire. Roof overhangs can be a greater challenge to fire-proof than metal overhangs directly above a south-facing window (see resource #2 for example images).
ACTION
» Specify fixed horizontal metal overhangs above south-facing windows in place of a roof-overhang. Determine overhang lengths by calculating the length needed to shield summer insolation, but allow winter sun penetration.
» For added resilience, specify exterior operable metal louvers in place of fixed overhangs, to shade south, east and west windows from sun and completely cover windows during a fire or high wind event for added protection. Exterior louvers are particularly useful for east and west orientations, which experience low sun angles that are hard to shade with overhangs.
» If using a roof or non-metal overhang, enclose the underside with a minimum of one-hour fire-rated horizontal soffit that shields all joints, rafters, and trusses from embers and hot gasses.
RESOURCES
22. Design outdoor spaces as ground-flush patios or use fire-resistant decking materials.
Local regulation may soon mandate that zero combustible material lay within 5 feet of the building footprint. This will likely include decking material. Decks can easily trap embers and are sometimes the first ignition point of a home fire.
ACTION
» In place of above-ground decks, build patios that are flush with the ground to prevent areas for combustible debris to get trapped. Specify non-combustible patio materials (e.g. concrete, stone, tile).
» When designing decks, orient away from typical wildfire path and away from vegetation. Use non-combustible deck materials (see resource #2 for examples) and cover underside with gypsum or metal soffit.
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Envelope Materials
23. Specify exterior walls with wood or metal studs, continuous mineral wool insulation, and stucco, fiber-cement as cost-effective, fire-resilient wall components.
There are numerous envelope materials and assembly methods that support a highly airtight and fire-resistant envelope. The cheapest option is typically a wood-framed structure with fire-resilient mineral-wool continuous insulation and cement-stucco or fiber-cement siding. The Headwater Economic’s study on building costs found this wall type saves costs and also adds to fire-resilience. Provide a drainscreen (capillary break and gravity drainage space between the exterior cladding and a weather resistant barrier such as housewrap). If vented rainscreen construction detail is used in frame wall construction (vented air space beneath siding), screen all openings into the airspace with maximum 1⁄8-inch screening. Reduce thermal bridging with proper heat-transfer-resistant wall assembly components to minimize the transfer of wildfire heat indoors.
For a slight cost premium, specify insulated concrete forms (ICF) (e.g. RASTRA-type recycled styrofoam plus concrete blocks), autoclaved aerated concrete (AAC) (e.g. Aercon AAC), or metal siding, which are excellent fire-resistant options for exterior walls.
RESOURCES
24. Specify metal, concrete, tile, or slate roofing to withstand direct contact with burning material.
Roof materials should be able to withstand direct contact with burning material for extended periods of time. The roof design also needs to minimize seams and openings that can trap highly combustible debris. A metal roof is generally preferred as there will be fewer gaps where debris can accumulate and ignite in a fire. With concrete, tile, and slate roofing, select tightly fitting shingles or tiles without gaps where debris can accumulate. Avoid barrel tiles or high-profile S-tiles if possible, because the bird-excluding plugs at the eaves often fall out, allowing birds to build nests or debris to accumulate. If barrel or high-profile S-tiles are used, incorporate bird stops and ensure that they have been properly installed; inspect bird stops annually in advance of the dry season.
Consider gypsum, perlite, or other fire-proofing roof sheathing in place of standard plywood or oriented strandboard (OSB). For a small cost premium, specify GAF VeraShield Fire-resistant Roof Deck Protection as your roof sheathing.
RESOURCES
25. Specify fire-rated double-paned, or triple-paned, low-e windows and fire-rated exterior doors.
Windows can be the weakest link in a home’s envelope. Radiant heat can shatter windows opening the interior to embers. Higher performance (beyond code-compliant) windows provide both energy efficiency and fire resistance.
ACTION
» Specify tempered glass on the exterior pane of double-paned windows to decrease the window’s likelihood of being compromised. Avoid plastic bubble skylights, annealed glass, or ceramic glass as they are most susceptible to compromise in a fire. Use only metal, metal-clad wood frames, or fire-rated fiberglass frames. Steel is the most fire-resistant frame and vinyl is the worst. Ensure the frame is thermally broken, which reduces the transfer of heat between the outside and inside. For maximum fire resistance and efficiency, specify triple-paned windows with fire-rated glass.
» Specify a door and assembly hardware that is fire-rated to at least 75% of the exterior wall’s fire rating. Install metal, insulated garage doors. Apply weatherstripping to all edges.
» For added security, install fire-rated metal shutters that can come down in front of windows and doors (e.g. Alpine® Fire-Shut® Coiling Fire Shutters). Choose a shutter systems that automatically closes in the event of fire via heat activated fusible links. Ask your prospective insurance providers whether they provide a discount for installing fire shutters.
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Construction Method
26. Use Prefabricated construction to improve build quality and reduce construction time.
Poor build quality can leave a home more susceptible to ignition. Finding a contractor who can supply a high quality of construction can be a challenge when a large number of projects are competing for talent. Therefore, consider factory- built components or whole buildings that specifically guarantee a level of airtightness, energy efficiency and fire resilience. As with site-built construction, not all prefab companies are the same, but building in a factory can provide tighter quality control to achieve a high performance building envelope when it is specified. Because prefab buildings and building components need to withstand forces of transportation to the site, they are also built with added structural integrity— often enough to withstand a Richter 8 earthquake.
ACTION
» To reduce construction time, use prefab components to begin building the home while foundation and utility work is being completed on-site. A shortened work schedule means lower overall costs for labor and equipment. Also, many prefab companies are discounting their prices for those rebuilding from a fire.
» Before signing with a prefab company, ask them whether they guarantee airtightness and energy efficiency up to a particular level. If you are using one of the prefab company’s designs, ensure that their design details meet Wildfire Urban Interface (WUI) codes and that the home meets most of the fire-resilient design recommendations outlined in this document.
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Water Systems
27. Install an on-site water storage tank with backup power for pumping or design for gravity-fed water distribution.
During a wildfire, conventional water supplies are often exhausted by firefighters. Having an auxiliary water supply can help to supply hoses, sprinkler systems, and other critical water uses. Water availability may also encourage firefighters to station at your home, greatly reducing the chances of a home ignition.
ACTION
» Store water in a concrete, fiberglass, or metal tank (not plastic) and locate it in crawlspace, basement, or outdoors (ideally underground if coupled with back-up pumping power). Ensure that pumping can be carried out without grid- supplied electricity. This can be accomplished by wiring pumps to run on on-site power or by raising the water tank high enough to allow gravity to pressurize the water system
» To mitigate potable water costs, consider using greywater, which is relatively clean wastewater from sinks, showers, and washing machines, to supply the water tank. Note, greywater does not include wastewater from toilets, which is called blackwater. Grey water will need some filtration and treatment for prolonged storage and cannot be used for potable water uses. If you choose to supply the water tank with rainwater, it should be designed to also accept well or utilities-supplied water so drought conditions don’t also deplete your stored water supply. Often one significant rainfall event is enough to fill a large tank if you collect for the full roof area.
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28. Install exterior sprinklers supplied from stored water and powered by back-up power system.
Exterior sprinklers are typically placed on the underside of a roof overhang or on the roof itself. Such systems can significantly lower risk of home ignition and can sometimes help justify an insurance discount. Consider adding a pressurized holding tank (see recommendation #27) to ensure the availability of water in the event that the normal water supply is depleted.
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29. Prioritize an efficient water heating system.
Likely one of the largest portions of an energy bill in this region is water heating. Therefore, to reduce energy consumption, prioritize first using less hot water (with super efficient showerheads, washing machines and dishwashers), and then heating water efficiently. Efficient electric heat pump water heating systems are a good place to start. Solar thermal water heating is another good option. In addition to Southern California Edison’s (SCE) $5,000 incentive for an all-electric home, SCE gives a $500 rebate on a number of energy-efficient appliances (see resources below for example products). In addition, washing clothes on the cold cycle can reduce washing machine energy usage by as much as 80%.
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Heating, Ventilation, & Cooling Strategy
30. Use Mini-split ductless heating and cooling systems to reduce ducts and control air conditioning room by room.
Because Malibu’s climate is so temperate, thermal conditioning needs are minimal and only necessary for a small portion of the year. Many choose to include A/C solely for home resale value.
ACTION
» Heat and cool with a ductless mini-split system to save energy, minimize envelope openings, and to eliminate large ducts and the attics and crawl spaces where ducts are typically located. These indoor units are supplied by refrigerant lines, so there are no air ducts from the outside. Fewer envelope openings and air ducts reduce the chance of embers entering the home. Because multiple units are located throughout the home (typically one per room, or zones), ductless mini-split systems enable more control to heat or cool only the areas of the home that are in use (e.g. cool only bedrooms at night).
» As ductless mini-split systems only heat and cool the air, a separate fresh air ventilation strategy is necessary. This can be done with bathroom and kitchen exhaust and minimal trickle vents for additional air, or with a heat recovery ventilator system, which is more energy efficient but more costly. In the latter case, you can group vents into one point for air intake and one for exhaust for added fire resilience (see recommendation #18).
» As an energy efficient, but much costlier alternative to the ductless mini-split, install an air-to-water heat pump or ground source heat pump with hot and cold water distribution through radiant flooring or ceiling panels. This too would minimize envelope openings and ductwork. Radiant floors are considered to provide the highest quality thermal comfort by warming surfaces first rather than the air first. If you do use ducted air distribution, heat pumps can also be used to warm or cool incoming air.
RESOURCES
31. Protect all necessary vent openings with metal mesh screening and fire damper with fusible links.
In wildfire events, poorly designed vents can melt or allow hot air and embers to backdraft into the home.
ACTION
» Include automatic back-draft dampers and fire-rated assemblies for all bathroom, dryer, and kitchen vents. If you choose to design vented attic or crawlspace, use a maximum of 1⁄8-inch metal mesh to cover all vents. For gable- end vents and crawl-space vents, consider a metal hinged shutter that can be latched close in the event of a fire or, for louvers, ensure metal blades are adjustable and can be manually closed. Sheath plastic plumbing vents with metal sleeves and hoods. To automate the vent-closing process, use fire dampers with fusible links that will automatically close metal blades above a certain temperature (typically 165°F).
RESOURCES
CalFire Fire-resistant Decking Material Database (search for Decking in Category)
FEMA. (2008). Vents - Homeowner’s Guide to Construction in Wildfire Zones
32. Incorporate air filtration into the ventilation system or purchase portable air purifiers with HEPA filter to protect against fine particulate matter in smoke.
Smoke inhalation can be a significant danger to the health of those nearby a wildfire. Even wildfires hundreds of miles away can impact your air quality. With wildfire incidents expected to rise in the coming years, a high-performance air purification system is essential. This is especially important for those who stay in their homes during a fire of close proximity. The particulate matter that makes wildfire smoke so dangerous is extremely small (0.4-0.7 microns), which passes through most air filters.
ACTION
» Install a HEPA certified filter to catch 99.97% of particulate matter as small as 0.3 microns. Change filters every 12-18 months or earlier in the event of a nearby wildfire.
Energy Systems
33. Design an all-electric home; install only electric equipment and appliances.
Electric grid utility companies encourage new construction projects to design out natural gas or oil supply lines and instead install only electric-source equipment and appliances. The benefit is not only lower greenhouse-gas emissions (getting ever-lower as SCE decarbonizes) but also improved safety and resilience by negating the risk of pipeline cracks and explosions. SCE has recently released a major financial incentive to encourage rebuilders to do so.
The CLEAR program offers an additional incentive of up to $5,000 for an all-electric home (see recommendation #10). In most cases, the switch to electricity can be done for little to no cost premium, freeing up much of the incentive to go toward other design features like solar panels or a metal roof. The most common gas- or oil-fueled equipment includes furnaces, hot water heaters, dryers, and oven/stovetop; each of these can be readily replaced with a cost-effective electric alternatives.
34. Install photovoltaic panels (solar panels) and a battery system with the capability to “island”.
Energy rates are expected to rise in the coming years. Solar panels are increasingly cost effective, with investments typically returned (via reduced energy bill) in 5-7 years—without accounting for state and federal incentives. There are a number of incentive programs including a 26% federal tax rebate, and a $5,000 SCE incentive when solar is paired with batteries. For more information on incentives and financing options see recommendations #8–11. On-site power is also one of the foundational elements of resilient design, allowing the use of critical electrical equipment in the event of a power outage. Ensure that the system you choose has an inverter with the capability to disconnect from the grid (i.e. to island) when power is down so that your system will remain functioning without harm to the utility service workers.
On average, the energy use of a modest, efficiently designed Malibu home can be offset with a 4-8 kW solar PV array. A ballpark cost to buy and install a solar PV array is $3.53/watt-installed, or $17,650 for a 5kW system before state and federal incentives. Financed over 20 years using PACE, it would hypothetically increase a monthly mortgage payment by $74 (or ~$50 after incentives), which would be largely offset by a reduced or non-existent energy bill. This also locks in the price you pay for energy irrespective of the expected ballooning of electricity costs.
Battery systems can cost between $0.45-0.70/Wh. As an example, a Tesla Powerwall 2 costs $6,700 (not including installation costs). With a 26% federal tax rebate and the CLEAR program incentive ($5,000), the cost would be almost negligible.
ACTION
» Use the online PVWatts tool (resource #3) to estimate pv sizing for your home. In deciding where to site solar PV, consider prevailing wind speed/direction, roof orientation and available space on an accessory dwelling unit (ADU) or the ground. Ground-mounted panels can be cheaper and take away the risk of roof-mounting equipment accumulating plant litter and trapping fire embers. However, the PV system is more likely to get damaged in a wildfire when sited on the ground (especially near vegetation). Battery equipment can be sited underground to minimize fire vulnerability.
RESOURCES
35. Wire your back-up power system to supply a critical load circuit in the event of a power outage.
Because your back-up power system will likely be sized to supply less than your normal electric load, your house should be wired with a critical-load circuit that only supplies power to electrical loads that you deem most important to life and home safety. Critical loads may include water pumps, pumped wastewater components of septic system, WiFi cable and wireless router, some lighting, some outlets for plug loads, some cooking (e.g. microwave), refrigerator and freezer, television or radio for emergency broadcasts, electrical components of heating equipment, cooling fans (refrigerant-cycle air conditioning usually consumes too much power), garage door openers, any needed medical equipment (e.g. oxygen concentrator).