Here Are More Examples of Concrete Construction and Fire Resistant Roofing  

My previous two columns about reducing your home’s vulnerability to wildfires generated a lot of reader response, providing even more to write about on this important subject.

Fire resistance is personal for Rita and me, since we live in a wood frame home backing to open space which would be ready fuel for a wildfire.

I’ve been told that following an 1863 fire, Denver passed an ordinance requiring masonry construction. Somewhere along the line, that requirement was dropped. I wouldn’t be surprised to see building codes changed once again restricting wood construction.

While there’s a trend toward requiring  fire suppression systems inside homes, they are designed to suppress fires which originate inside a home.  If a fire originates externally, such systems may be of limited effectiveness in saving a structure.

Last week I wrote about ICFs — insulated concrete forms. Concrete is poured into a form which has insulating EPS (expanded polystyrene) on each side. This produces a concrete wall which has insulation pre-installed on each side of it.

A couple readers made me aware of the opposite approach, a concrete wall in which the “sandwich” has concrete on the outside and the expanded polystyrene on the inside.

Reader Lynn Greene invited me to visit her home in Perry Park (see picture below), southwest of Castle Rock, which was built with Thermomass® walls and concrete floors developed by Composite Technologies Corporation of Boone, Iowa.

Lynn’s tenant told me that the energy costs peak out at about $70 per month to heat the house with radiant floor heating built into the concrete floors. That heat is provided by a high efficiency boiler using natural gas. Large south-facing windows provide a lot of free winter time heating. (Notice the large overhangs shading the south-facing windows in summer but not in the winter.)

The Thermomass walls were poured in place, less expensive and more attractive than walls built of uninsulated concrete block. It also allowed electrical and other conduits to be built into the walls instead of surface mounted afterward.

Another “sandwich” approach is sold by a company called RSG 3-D, but they create panels which are assembled onsite instead of being poured in place. Also, their polystyrene interiors (which are wider) have steel connectors instead of the plastic connectors used in the Thermomass walls. That reduces the insulating quality of the wall, since metal is a conductor.

Another reader reminded me that the making of concrete is a major source of carbon dioxide, a greenhouse gas. According to Wikipedia, “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.”

Click here to read an article from The Guardian about the development of “green concrete” in Australia that sounds very promising. As you may know, “concrete is made from approximately 10% Portland cement, 3% supplementary cementitious inclusion (for example fly ash), 80% aggregates (such as gravel and sand), and 7% water.” Then it is reinforced with steel, which has its own huge carbon footprint.  By replacing the steel with recycled plastic, that impact is mitigated, and, according to article from The Guardian, the Australian company Wagners has created earth friendly concrete using blast furnace slag – an industrial waste from steel production – along with fly ash, a waste from coal power generation, as a replacement for Portland cement.

To make a concrete home truly resistant to wildfire, it is necessary to make the windows and doors and other openings fire resistant too. There is glass (with frames) rated for 20 to 180 minutes of fire resistance. See

Lastly, one must deal with roofing. Another reader made me aware of the synthetic roofing by CeDUR which was installed on her Wheat Ridge home and which is also on Woody’s Wood-Fired Pizza:

It looks just like a wood shake roof and is installed the same way in individual shakes, but it has the highest rating of fire resistance (Class A), earning homeowners a substantial discount on their homeowners insurance. Learn more at

There are vents of all kinds not only on your roof but on soffits, foundations, eaves and gables, and they need to be protected from flying embers. Vulcan Vent sells vents for all those openings, “built to create a barrier against wind-blown embers and flames in the presence of intense heat.” Learn more about them at

Homes Built of Concrete Garner Increased Interest in Wake of the Marshall Fire  

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:

Photo by Sara Vestal, Teller County HFH

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 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.