Concrete Homes – Golden Real Estate's Blog

AirCrete Is a Lighter, More Climate-Friendly Version of Concrete for Home Building

Back in January, in response to the destruction of the Marshall Fire, I wrote about various building techniques and materials, including concrete, that could make homes more fire resistant than today’s common wood-frame tract homes.

Last week a reader shared a recent article on Treehugger.com about AirCrete, “a foamy mixture of air bubbles and cement that is cheap to make, water-resistant, fireproof, and [Do-It-Yourself]-friendly.” Here’s a link to that full article. There’s a 7-minute YouTube video within the article that describes the process.

The process is the brainchild of Hajjar Gibran, the great-nephew of the poet Kahlil Gibran. His enterprise sells the tools for creating AirCrete using locally obtained cement. The only other ingredients are water and your choice of a degreasing dish detergent to create the foam using a 120V foam injection mixer which they sell for $199 on their website, www.domegaia.com. For $95, Mr. Gibran himself will provide a professional AirCrete consultation, or, for $700 tuition, you can attend a 10-day workshop.

Although the organization is focused on building domes, it’s clear that the process can be used to build other types of structures. With total structural building costs in the $2,000 to $9,000 range, the process is marketed specifically for building “tiny homes,” and would, it seems, provide an affordable way of addressing the problem of homelessness. I’d love to see it used here in Colorado!

Regular concrete has a low R-value, the common measurement of insulation — 0.1 to 0.2 per inch of thickness. Because of the air bubbles within it, the R-value of AirCrete is 6 per inch of thickness. This is roughly twice the insulating value of a typical 2×4 wood-frame wall filled with blown-in cellulose.

As I noted in my earlier columns, the manufacture of Portland cement is a major contributor to global warming, responsible for an estimated 7% of all greenhouse gas emissions worldwide. Because AirCrete is mostly air, its use of cement is far less than an equivalent volume of traditional concrete.

According to the Treehugger.com article, “The blend creates a lightweight and low-cost building block that is fireproof, water-resistant, insect-proof, and serves to insulate the building. According to its creator, AirCrete offers many desirable attributes for use as a building material for single-story residences, especially for the owner-builder, among them the ability to cut construction costs by a factor of 10 when compared with conventional construction.”

The article continues: “Beyond its affordability, DomeGaia says their AirCrete is easy to work with, drying in just one night and flexible enough to be shaped into almost any form. You can use your standard wood-working tools to carve or drill into the material, inserting screws and nails where necessary. Since the material hardens as time passes, you can be more confident about the shape you settle on instead of being increasingly worried about future vulnerabilities.”

DomeGaia’s workshops sound like a variation on eco-tourism, because they involve building an actual dome home (probably in a third world country) using AirCrete. Here is an excerpt from DomeGaia’s web page about the workshops:

“This is a hands on workshop, meaning most of the time spent will be outside and actively building. Though there will be some down time when instructors explain the building process and answer questions, you will still be on the building site as these explanations take place, so please come prepared against the elements…. DomeGaia workshops usually include time for yoga, guided meditations, dance, music, and exploring local attractions! Make new friends from around the world, learning, laughing and building together.”

Their website invites you to sign up for a monthly newsletter so you will be notified of upcoming workshops and their locations.

My thanks to the reader who shared AirCrete with me. I welcome your input, too, and let me know if you attend a DomeGaia workshop!

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 www.fireglass.com.

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 www.cedur.com/fire-safety.

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 www.VulcanVents.com.

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:

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.