Fire Proofing New Home Construction


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Boulder County, and most of the Front Range of Colorado, watched in horror as the wind-driven Marshall fire consumed over 1,000 homes and structures, displacing many of our friends and neighbors.

A new hotel in Superior burned to the ground, and the Tesla building, saved through the efforts of local firemen, has now been stripped to its steel frame. At least one house that I built in Louisville was lost, so it hit home with me.

These home fires all had one thing in common, they were not ignited from the usual means of cooking, faulty electrical or heating, or smoking. They were ignited by an external event, a wind-driven wildfire.

To catch fire, one of two things occurred: The exterior material caught fire, or embers made it into the interior of the house.

Having developed construction technologies, and studied what is available to home builders, I have been curious about building fire-resistant homes. After the Sunshine Canyon fire some years ago, I investigated concrete walls. Most of us are familiar with Insulated Concrete Forms (ICF). There are many advantages of those systems (heat retention, sound attenuation, lifecycle, insect resistance).

These concrete core walls are more resistant to fire, although the foam exterior can burn if not well protected with hard coat stucco or fire-resistant siding.

Another concrete system places the foam insulation between 2 layers of concrete, making it fireproof (and, I suppose, bulletproof as well). Leviat Corp offers the original Thermomass system, and it has been in the market for some time. This “concrete sandwich” is created by special spacers to hold a rigid foam insulating panel between concrete forms. Concrete is then poured down both sides of the form. Precast panels of a similar design are also available.

In some countries, the same thing is accomplished by placing the rigid insulation between 2 courses of cinder block, and this sandwich can also be utilized in tilt up walls.

I recently inspected two homes destroyed by the Marshall fire. Both had concrete and steel composite floor garages installed over an additional garage space in the basement. While these homes burned to the ground, both garage decks remained intact. One had severe warping, probably due to burning automobile fuel. The other appears to be charred only. Neither contributed to the fire’s fuel source.

Marshall fire
Image: Jon Williams

Most builders, however, want to harden their current building techniques against the chance of fire infiltrating the structure in a grass or forest fire.

Certainly, concrete siding, soffits and fascia boards are less flammable than wood siding, and have high market penetration. That is a good start.

When I was a kid, we sold old wooden roof shingles as kindling. I don’t think many homes are built with that type of roof anymore. Many of our older homes, especially in the mountains, have old cedar roofs that can ignite instantly and spread rapidly. Shake roofs typically have no fire rating. Modern asphalt shingle, metal roofs and concrete tile, on the other hand, all carry Class A fire ratings, while synthetic roof tiles are typically Class C.

As far as keeping embers out of the house, the fenestration of the home must be addressed. Wood windows can either burn from the outside, or break under extreme heat or when struck by large flying embers.

Fire resistant window frame material, in descending order, are aluminum or aluminum clad wood windows, followed by fiberglass windows. Any of these are a good option when properly installed.

To avoid embers entering the building envelope, tempered glass window panes and metal screens will give better protection than standard glass and plastic screens.

Once one has committed to the measures, it is important to seal the house with a high quality firestop caulk. This will keep small embers from lodging under the siding and possibly igniting the framing members.

RELATED: Wildfire Mitigation and Prevention

Do not forget the inside of the home. While the catastrophic type of wildfires we see in the west get the big headlines, most house fires start from within. Be sure your electrical and heating systems exceed codes. Sealed burner fireplaces are certainly safe when properly used and installed. Concrete floors and steel framing are also options that can help harden a new home against fire.

I love to cook on an open flame. However, the advent of induction cooking surfaces offers new home buyers an excellent heat source without the flame and gas.

Once a spark infiltrates the home, it can ignite the contents and interior surfaces. I have been intrigued by fiberglass faced drywall for mold prevention. It seems like it would resist fire better than paper faced wall boards.

Our homes are full of flammable items, from bed sheets to magazines, to wood furniture, it all needs to be protected.

Following some common sense measures to keep the fire out and making sure the exterior is fire resistant, will go a long way to preventing the kind of devastating loss we have seen all too often in our communities.

Jon Williams
Jon Williams
Jonathan P. Williams is manager of FloR Systems LLC, a developer and provider of elevated structural concrete floors. He can be reached at [email protected].


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