fighting wildfires with building design

The ongoing Fourmile Canyon fire immediately west of Boulder has brought to light the necessity of doing the work to make “defensible space” around your home.  In a city like Chicago, defensible space  means good lighting and safe streets, but here in the Rocky Mountain West it means wildfire mitigation and ignition resistant construction.  It is not only for new construction, every property owner should take heed and can take action now to help protect themselves and their property.

few or no trees immediately surrounding house
vegetation cleared from around house

Boulder County has a two-pronged approach to designing houses and landscapes that can withstand moderate wildfires.  The first is by using only building materials that are ignition resistant.  This does not mean fireproof, but does mean avoiding the use of wood roofing, as in shakes and shingles, and decks.  Even on vertical surfaces, like siding, the wood materials are to be backed by a layer of 5/8″ thick fire resistant gypsum sheathing.  The day of the start of the Fourmile wildfire had the humidity at less than 10%.  If you combine that with the drying effect of high altitude sun, you will see that any exposed wood, in just a season or two, quickly becomes blistered and cracked and is prime kindling.  Thicker sections of wood, like heavy timber are acceptable as they generally surface burn leaving enough material unharmed within to still provide sufficient structural integrity.  The most common mistake is to not fireproof the undersides of overhanging decks and eaves.  Hot gases and embers roll uphill and can catch underneath these projections igniting the entire structure.

very little or no exposed wood and distance between trees and structures
ignition resistant stucco and concrete

Of course most of the concern in these mountainous wildfire zones is concentrated on not starting fires in the first place.  Any houses larger than 3,600 square feet are required to be sprinklered and many locations require substantial fire-fighting water storage cisterns to run that system for a period of time.  A recent project of ours required a 30,000 gallon cistern – about a swimming pool’s worth of water – to be stored on site in semi-buried tanks with fire hose connections.  Fires that start inside houses should not be allowed to set the entire mountain of fire.

hardscape surrounding house
hardscapes around house can be beautiful, not stark

The final part of the defensible space planning is to undertake wildfire mitigation efforts.  These can be done with new or existing structures and essentially boils down to getting rid of wildfire fuels around the immediate area of the house.  It does not mean that you have to live within a perimeter of gravel, but there are zones extending out from the house that reduce bushes and trees to create a fire break between the structure and the surrounding forest.  These zones are based on Boulder County’s Wildfire Mitigation Plan requirements and, in the case of new construction, are inspected prior to occupation of the finished building.

Wildfire Mitigation Plan with defensible zones

It is often painful to cut down trees and remove plantings on the beautiful sites that client’s choose to live.  We architects often complain that the wildfire field inspectors are a bit too quick to clear-cut a hillside.  When we lived up in the mountains it was a hard and painful task, but I cut down some 20+ trees from the area immediately surrounding our house and put many of these zone precautions in place.  This fire should remind us all that these are all simple and necessary parts of living in the mountainous West.

ignition resistant construction
transitions from natural to man-made landscape surrounding house

None of these actions will guarantee that a fire does not devastate your house and property.  However, taking these necessary steps will help the firefighters save your home and will demonstrate to them that you have done all you could do to keep them safe while they work to save your house.

Hoping that all the houses shown above, homes of clients and friends, all located in or near the evacuation zone, are safe in the current fire.  Anyone not in the immediate fire zone but still up in the wildfire interface area of the mountains, contact Boulder County Land Use or the Colorado State Forestry department and they can conduct a review of your property and give great advice on how to take the best measures to protect your house and your selves.  Please do it now.


2 thoughts on “fighting wildfires with building design

  1. I really enjoyed your post on building homes to withstand fire dangers in the west. Not only is it a practical means of fire protection for living in the west, it is also a low maintenance, cost effective and beautiful way to build. With your permission i would like to share this post with some of my readers.

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