Living with Fire – Part 3: Home Construction And Retrofitting For Fire Survivability
Living with Fire is a 4-part series presenting a new paradigm regarding fire – one in which we celebrate fire’s necessary ecological role, and design for a healthy relationship with it. The earlier parts of this series are:
- Living with Fire – Part 1: Personal Responsibility, Basic Fire Science, and Site Selection
- Living with Fire – Part 2: Regenerative Firescaping and Protecting Your Home with Good Design
Once a house has been sited to best minimize the fire sectors, and the landscape around the homesite has been designed and tended to provide a barrier in the event of fire along those sectors, a home’s exposure to fire will be significantly lessened. Attention to home construction will further reduce the chances of loss.
New Construction: Building A Fire-Resistant Home
Historically, homes in fire-prone areas have been built with highly flammable materials. The matchsticks (kiln-dried, highly flammable lumber) that many houses are framed, sided, and roofed with have ensured the demise of many houses in recent times.
Now, the many industrial materials used in modern construction are available in a wide range of fire-resistance levels, and there are many choices in constructing conventional homes for improved fire survivability. That information is readily available from many other sources, such as the National Fire Prevention Association and Ready for Wildfire websites, in far greater detail than we would choose to provide here. So, we will be approaching this section from the less-often discussed end of the home construction spectrum: natural building (this is 7th Generation Design after all!).
Fire-Resistant Building Materials
If we choose to live in a fire climate, it would make sense to build homes with materials that are either highly fire-resistant or even fireproof. The various geological building materials top the list for being fireproof:
- Cob – mix of clay, sand and straw used to create monolithic walls.
- Stone – more often seen in foundations, less frequently in whole house construction.
- Compressed earth blocks, adobe, super adobe.
- Earth bag construction – woven polyethylene bags filled with earth, compressed and stacked in place to form walls, typically coated with earthen or cement plaster.
- Straw bale construction – straw bales are actually very difficult to light on fire, and when covered with layers of cob or earthen plaster are even more so.
- Earth-bermed homes – set into a hillside or sloping ground so that earth quite literally creates the walls. Earthships, WOFATI’s and Oehler style earth bermed homes all employ this method.
- Metal roofing – has high fire-resistance. If radiant heat risk is high during a fire metal roofs can melt or transmit so much heat through them as to combust what is on the inside. Non-flammable or highly fire resistant insulation (mineral wool, seagrass, sawdust, feather, wool) will help reduce this potentiality.
- Slate/stone roofing – expensive, but obviously very fire-proof.
- Fire-resistant shingling – can be purchased or repurposed.
- If going the repurposed route, creative solutions abound – there are roofs made from old car doors, tin cans, metal barrels cut open and laid flat, and so much more.
- Ferrocement – often seen in Earthship designs for lightweight, curved, waterproof and fireproof roofs, ferrocement is an industrial product and will require a significant amount of metal rebar and lathe/wire to create the form, but it is long lasting and provides a number of very valuable functions to a built structure.
Retrofitting Existing Homes (Conventionally-Built Or Otherwise)
If you own an existing home, there are still many things that can be done to reduce the risk of loss in the event of a fire. Some of these include:
- Screen all vents – ¼” mesh screens will NOT stop embers! Retrofit attic vents, under house vents and any other vent or gap by which embers might enter the home with ⅛” metal screen. Do not use vinyl/plastic screens as they run the risk of melting due to radiant heat.
- Fire shutters – install metal shutters that are closed from the outside, designed to reduce radiant heat transmission through windows to objects inside the home. If windows from the home have direct line of sight to large amounts of fuels within 100’ of the home consider this option.
- Replace wood shingles – wood shingle roofs dramatically increase a home’s chance of igniting and suffering catastrophic damage by as much as 700%. Choose non-flammable or fire-resistant roofing materials and insulation.
- Replace exposed wood siding – while less dangerous than wood-shingled roofs, wooden siding also increases ignition risk significantly. Choose non-flammable or fire-resistant materials if able.
- Consider repainting the home with white paint or a similar light shade to help reduce radiant heat gain in the event of a fire.
- Indoor fire sprinklers – to read more, visit the National Fire Prevention Association website.
- Outdoor fire sprinklers – especially important for homes with extended decks, roofs with valleys, nooks and crannies, or soffets.
- If you have a wooden deck, it either should be very low or very high off the ground. Can you stuff a garbage bag of leaves under your wooden deck? If you can, you need to make your deck a patio of rock or concrete – unless you have a very capable WEEDS Fire System, and even still, fire-proof materials are preferable.
Fire shelters are not part of the mainstream lexicon of fire preparedness, which is unfortunate as they have the potential to save lives in the case of a fast moving fire that blows over an area with little to no warning. While in many cases it is safest to evacuate, if you’re late to the game and the roads are packed, it may well be safer to be in a properly designed and stocked fire shelter than sitting in bumper to bumper traffic while flames burn all around you.
Ideally a fire shelter would be set into the earth and have a curved “snailshell” style entry way made of heavy geologic materials (stone, cob, adobe, earth bag etc) to prevent direct radiation of heat to the interior. If built above ground, the walls need to be constructed with heavy geologic materials that can protect from radiant heat exposure – cob, adobe, earth bag, stone, other geologic building materials.
A fire shelter should at minimum be stocked with short to mid-term survival supplies – non-perishable food, water, emergency first aid supplies, blankets. Additional items that can be stored here include home fire-fighting equipment (pumps, hoses, fire suits, respirators, supplemental oxygen and other safety gear), communication gear (radios, off-grid power supplies) and longer term survival necessities (water purification systems, bulk non-perishable food, sleeping gear etc).
While all this preparation may sound rather dire and morbid, for properties located in high fire danger areas with limited routes in and out, having a fire shelter could mean the difference between life and death. A fire shelter also provides a safe storage location for supplies that could make your life a lot more comfortable following a devastating wildfire, as well as put you in a position to help neighbors and other less fortunate than yourself. And it can be put to good use as a kids fort when times are good!
Outdoor Fire Sprinklers
Fire sprinklers are very effective at dousing wind-borne embers, provided they are spraying where embers are landing. Fire sprinklers are generally installed along the eaves or roofline of a home and spray down and out – to wet both the surrounding ground and the sides of the house. Additional sprinklers may be added in vulnerable spots like soffets and rooftops as well to douse embers that land directly on the rooftop or settle in roof valleys. While there aren’t many controlled studies on these types of systems, initial data and ample anecdotal evidence suggests that a Wind-Enabled Ember Dousing System (WEEDS) style fire sprinkler system increases home survivability by 7 times over having just defensible space around a home.
The principles for designing an effective outdoor fire sprinkler system following the WEEDS protocol are as follows:
- Direct spray into the wind – Use the fire-generated winds to blow spray back onto the structure, this maximizes windward protection, and the water ends up where the embers are (a thorough sector analysis, as described in the permaculture design approach, will identify the avenues of the primary fire + wind threats).
- Use a low flow rate – better to have the system able to run lightly but consistently for a longer period of time, than a heavy deluge for a shorter period of time.
- < 30 gallons per minute total flow rate will enable a system with a 5000 gallon water tank to run for at least 3 hours.
- Low spray densities are all it takes to protect from firebrands (this is not the case with radiant heat, however).
- Have a dedicated water supply (tank) to run this system.
- Often times municipal water will be shut off or pressure will be very low from high demands elsewhere due to the fire, and as such should not be counted on to effectively or reliably run a WEEDS sprinkler system.
- Ideally the system should be gravity fed (tank sited well-uphill of home).
- If unable to obtain pressurized water using gravity, then a pump will be required, powered by a dedicated off-grid power source. Grid electricity cannot be relied upon during a wildfire. A propane-powered generator fed via an underground line would be most ideal. Tank, generator, pump and pressure tank protection from radiant heat also needs to be taken into account to ensure function during the time of fire blow-over.
Additional helpful design features might include…
- Metal piping and sprinklers should be used if radiant heat is a risk (i.e. large stands of fuels are within 100’ of the structure).
- Larger tanks (10,000 gallon) will increase the duration that the system can operate.
- Remote or automated triggering
- DO NOT use heat activation – typical of indoor sprinklers. By this time windows may be too hot and shatter from thermal shock.
For a quick risk assessment for your home complete with with fire risk reduction action steps use the UC Berkeley Home Fire Risk Assessment Checklist (takes 2 minutes to complete).
After The Fire Blows Over
Once the fire front has passed through, hopefully with an intact and undamaged home, remember that the danger is still high! As soon as it is safe to venture outside it’s time to start an ember watch while the fire is still burning closeby. Many times homes appear to survive the inferno only to be ignited several hours later by small embers that have slowly caught larger structures. Having pre-positioned trash cans filled with water and sacrificial towels or burlap sacks for this purpose can be helpful.
If you have a WEEDS fire sprinkler it should be left operating for several hours after the fire (hopefully it has been designed to have this capacity) to help ensure any remaining or new embers (backing winds can bring ember fall out back to previously burned areas) are either extinguished or unable to ignite any larger fuel source.
Continue on to the last part of our Living with Fire Series, Part 4: Integrating Fire Into Daily Life (Again)!