Santa Fe Habitat for Humanity is asking its volunteers to do something different this week and is inviting the public to come and watch. Instead of pounding wood together with hammers and nails, the organization will be stacking hollow blocks of insulating concrete forms.

When lumber prices went through the roof earlier this year, Habitat for Humanity International was approached by the National Ready Mix Concrete Association and the Insulating Concrete Forms Manufacturers Association with an offer of free material to be used in 16 locations across the country. Santa Fe was chosen, and two homes will be built in Oshara Village with the material beginning Monday.

Santa Fe is a market with a long history of using the insulating concrete forms for exterior walls. In the early days of the green building movement, the primary focus wasn’t energy and water conservation. It was “save the trees.” Because of that, ICFs established a strong foothold here.

That foothold became solid with the advent of Las Campanas in the late 1980s. One of its building covenants: the planes of window glass needed to be recessed at least

4 inches from the plane of exterior stucco so as to resemble thick adobe walls. That requirement drove a lot of builders to experiment with ICF exterior walls.

A typical ICF block has 2 inches of foam on each side of a hollow core, fastened together by plastic ties. Dimensions of blocks vary with manufacturers, but 16 inches tall by 4 feet long, by 10 inches wide is typical. One person can easily pick one up and stack it on top of another, meaning exterior walls go up very quickly.

Once the forms are stacked to the desired height (8 to 10 feet), and window and door openings are blocked out, a concrete pumper pours in a soupy concrete mix from the top. The concrete flows horizontally and vertically, filling tubular cores 4 to 6 inches thick. If the foam were stripped away, which it isn’t, one would see a lattice of concrete tubes. Reinforcing steel bars are embedded in the concrete to add strength.

As the green-building movement evolved, some began expressing concerns about the embodied energy inherent in expanded foam products like Styrofoam and in the manufacture of cement. Those concerns still exist, but there’s no doubt an ICF structure is solid and energy efficient. The walls are virtually soundproof and have none of the air leakage associated with even well-built frame walls. With drywall attached to the inside and cementitious stucco on the outside, they are also very fire-resistant.

Because the walls are double the thickness of standard frame construction, there is a sacrifice of interior space. In a 1,200-square-foot house, that could be a loss of as much as 100 square feet.

Habitat volunteers won’t be putting away their nail pouches anytime soon — interior walls and roof assemblies are still built as they always have been, but this week’s double-build could signal a new path for our local Habitat chapter.

Kim Shanahan has been a Santa Fe green builder since 1986 and a sustainability consultant since 2019. Contact him at shanafe@aol.com.

(3) comments

Keith Crow

Can you comment on the costs of construction for ICF vs frame vs adobe? Thanks.

KIM shanahna

Depends on the manufacturer, but generally considered in the R-22 range for standard dimensions, which put them in-line with codes. R-19 fiberglass batt is still the default requirement for our climate zone but most building science experts acknowledge that poor installation practices for batt insulation makes its effective R-value considerably lower. ICFs, on the other hand, are almost impossible to install incorrectly when it come to the effectiveness of its R value, meaning that its nominal R-22 is really R-22.

Richard Reinders

What is the R factor for these blocks?

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