Last week’s column focused on ways that homes can be made more fire-resistant, but there’s only so much you can do to protect wood frame homes from wildfires that are driven by hurricane force winds. Looking at neighborhoods where every home was reduced to its concrete foundation, it’s not hard to question that common method of construction.
Reader Peter Deem made me aware of the use of insulated concrete forms (ICFs) to construct the entire “envelope” of a house and pointed me to Don Clem of the National Ready Mixed Concrete Association, which has a local office in Denver. That organization, along with its Colorado affiliate and several concrete companies, sponsored an 18-townhome project in Woodland Park for Habitat for Humanity of Teller County last summer. Here’s a picture of those townhomes under construction:
I was first introduced to the use of ICFs when I participated in the 1994 Jimmy Carter Work Project on the Cheyenne River Sioux Indian Reservation in Eagle Butte SD. The 28 homes in that project were conventional wood frame (“stick-built”) homes, but the concrete foundations were poured into ICFs. An ICF replaces more common wood forms which have to be removed from the foundation after it cures. The ICF provides insulation in the form of two inches of expanded polystyrene (EPS) both inside and outside the foundation. After seeing it there, I was surprised not to see ICFs in widespread use for foundations by production builders over the past 27 years.
The ICFs being promoted now are for above-ground use for exterior walls, and there are even ICFs for pouring concrete flat roofs. (More commonly, there are concrete tile sloped roofs, including one on the house Rita and I once owned on Parfet Estates Drive in Golden.)
While concrete is a non-combustible material, the EPS insulating layers will melt with direct flame, but it does not act as a fuel source, will not promote flame spread, and will not release harmful gases. In addition, the ICF would be protected on the outside of a home by siding — for example, a fiber cement siding like Hardieboard, which is not combustible, and the flames would probably only be present briefly during a passing wildfire. The interior would be covered by drywall, as with a stick-built house.
Speaking of that, there is still the question of combustible vegetation such as juniper bushes that are close to your house. Another reader made me aware of Phos-Chek, the same fire retardant that you see used by aerial tankers to attack wildfires. While that chemical is red, it’s available in a colorless concentrate that you mix with water and apply using an ordinary sprayer to the vegetation around your home. A single bottle of Phos-Chek sufficient to make 5 gallons costs $59.99. You will need 5 to 20 gallons depending on the amount of vegetation you want to cover. Click here to view a KNBC news segment about a Malibu homeowner who saved her home from the Woolsey fire in November 2018 thanks to an application of Phos-Chek to the grounds around her house three months earlier.
In last week’s column I also mentioned that the soffit vents typical of homes with unconditioned attics can allow embers to enter the attic, igniting an interior fire, but I neglected to mention that there are ways to fireproof soffit vents to keep that from happening.
Another way that concrete homes are being built is using 3D printing pioneered by Icon, an Austin TX-based company which is currently building a 100-home Texas subdivision in partnership with Lennar using that process. Icon built its first 3D-printed home in 2018 as a proof of concept, following which they built a community of 3D-printed homes in Tabasco, Mexico. Here’s a picture of a Habitat for Humanity 3D-printed home in Virginia:
Just as desktop 3D printers work by applying multiple layers of material following a computerized template, Icon’s huge 3D printers apply multiple layers of concrete. See www.IconBuild.com for more information about this company, which, by the way, has NASA contracts to build 3D-printed structures on the moon and on Mars. Their primary mission, however, is “to re-imagine the approach to homebuilding and construction to make affordable, dignified housing available to everyone throughout the world.”
Their home page goes on to say, “the audacious mission of Icon is to revolutionize homebuilding, and our team’s expertise and determination have already made this dream a reality. Our team has a passion for design, engineering, and elegant software. We have decades of experience in sustainable technology and construction innovation.”
Building with concrete is both less labor intensive, less expensive and more sustainable than building with lumber. It’s significant that one of America’s biggest builders, Lennar, is working with Icon to build those 100 concrete homes in Texas. That project should provide facts and figures about the practicality and economy of building with concrete that could be a powerful influence on the rest of the home-building industry.
One thought on “Homes Built of Concrete Garner Increased Interest in Wake of the Marshall Fire ”
Hi Jim, I know you’re big on environmentalism. I have heard that concrete is not particularly green. Here’s a quick copy and paste from Wikipedia:
Carbon dioxide emissions and climate change
The cement industry is one of the two largest producers of carbon dioxide (CO2), creating up to 8% of worldwide man-made emissions of this gas, of which 50% is from the chemical process and 40% from burning fuel. The CO2 produced for the manufacture of structural concrete (using ~14% cement) is estimated at 410 kg/m3 (~180 kg/tonne @ density of 2.3 g/cm3) (reduced to 290 kg/m3 with 30% fly ash replacement of cement). The CO2 emission from the concrete production is directly proportional to the cement content used in the concrete mix; 900 kg of CO2 are emitted for the fabrication of every ton of cement, accounting for 88% of the emissions associated with the average concrete mix. Cement manufacture contributes greenhouse gases both directly through the production of carbon dioxide when calcium carbonate is thermally decomposed, producing lime and carbon dioxide, and also through the use of energy, particularly from the combustion of fossil fuels.
Just a head’s up.