Concrete is one of the most resistant substances to intense heat and fire. A finished ICF wall, mudded and taped, provides a solid concrete exterior with a 3-4 hour fire rating. According to the ICFA, concrete structures are more likely to remain standing through fire than structures of other materials. Unlike wood, concrete does not burn. Unlike steel, it does not soften and bend. Concrete does not break down until it is exposed to thousands of degrees Fahrenheit. The house shown above was built with Amvic’s Insulated Concrete Forms and was one of the few fortunate homes to survive the wildfire.
According to the California State Fire Marshall, most of the existing building code requirements that relate to fire danger have been derived from decades of experience in urban fires. While this experience remains valid, there is a process underway of study of the experiences of recent years from losses in wildfires in the west. Changes in the codes are being evaluated and will be forthcoming in the near future. Current minimum building codes prescribe standards that generally prove to be less than sufficient in a wildfire scenario. There are planned changes that will stiffen requirements in the future, but there are some simple steps that can be considered now in planning new construction in an area where wildfire is a threat. These design issues and practices can make the difference between destruction and survival. And the cost differences are generally minor.
The following are some suggestions to consider when building a fire safe home.
Exterior walls: You can build homes with essentially fireproof walls. One method of doing this would be to use Amvic insulated concrete wall system. An Insulated Concrete Form (ICF) wall provides a solid flat wall of concrete sandwiched between two layers of EPS foam. An ICF wall with a 6” core of solid concrete provides a building shell with a wall fire rating of greater than 3 hours.
Roofs: The other important detail of fire safe construction is using a fire-resistant roofing material. Class-A fiberglass, cement-tile or metal roof coverings should be used in designated high-hazard areas on all new construction, additions or repairs. Eave-end gaps in tile roofs should be fire-stopped with cement mortar or metal bird stops, which are available at most roofing supply stores.
Eves & Soffits: Do not leave exposed rafter tails. Enclose eves and rafter tails with a soffit of fireproof material. This can either be a fire resistant fiber-cement board product or stucco.
Decks: Use a fire proof or fire resistant material for decks. The best case is a concrete deck either as an ICF-formed concrete deck such as AmDeck™ or a concrete slab poured over a steel frame. Many modern synthetic materials are more resistant to fire than natural wood products.
- Skirt decks to within 6” of the ground with solid sides such that flying embers or a grass fire can’t get under the deck.
- Wood deck and trellis members should be a minimum 2×4 dimension; wood beams, floor joists and stair stringers a minimum 4×6 dimension; and posts a minimum 6×6 dimension.
- All such wood should be UBC-approved fire-retardant material or cement plastered.
All projections, such as roof overhangs, balconies, decks, exterior stairs, carports or patio covers, should be protected on their undersides and on exposed edges with cement plaster. Or they should be protected with a continuous wall, most likely poured-in-place concrete or cinder block, around the perimeter of the projection from the underside down to the existing grade; or with UBC approved fire-retardant wood specially treated with fire-retardant chemicals.
Propane tanks. Locate at least 30 feet away from the structure.
Defensible space and fire resistant materials. Follow State Fire Marshall guidelines. The same practices that apply to existing structures should be planned in for new construction.
For further information, there are numerous sources on Firesafe construction tips for new construction on the web. Some useful sites include:
- https://www.firewise.org
- https://www.firesafecouncil.org
- https://www.firewise.org/co/construction.html
Please note that this article is for educational purposes only – when designing your fire resistant home, please make sure you always consult with an architect or engineer first.