A Habitat for Humanity house on South Martin Luther King Jr. Drive shares an inside secret with a high-end development of lofts with views of the state Capitol, Union Station and the Arkansas River.
In both, outside walls are made of plastic foam and reinforced concrete.
Sounds a little strange. Maybe ugly, too.
Yet once exterior siding and interior drywall are in place, you’d never guess there is any difference between these concrete structures and neighboring houses whose walls were built using conventional 2-by-4 s and plywood sheathing.
Only the owners will know what’s inside their edifices — although there’s a chance they will boast about it.
That’s because their energy bills will be lower than those for conventional stick-built houses down the street. They’ll find their homes more immune to traffic and other noise pollution from outside. Their walls are also resistant to fire, mold, moisture and high winds.
The Habitat house’s and the loft’s walls are built using insulating concrete forms, commonly known as ICFs, for poured concrete walls. The forms are made from an expanded polystyrene, a plastic foam in which tiny pockets of air are trapped throughout, making it an efficient insulation. (It’s also a well-known packing material — think peanuts and Styrofoam. )
For the forms used in the Habitat and loft projects, the polystyrene is molded into lightweight interlocking hollow blocks, whose two sides are held together by plastic connectors. Construction crews stack the blocks into the shape of the building’s walls, adding reinforcing steel rebars as they go. Then concrete is poured inside. Even after the concrete has cured and hardened, the forms are left in place. They insulate the building and play other roles (more on that later ).
The link between the two buildings is Little Rock developer Matt Bell, a partner in the urban lofts project named Vertical.
Bell also owns Smart Structures, the Arkansas distributor of insulating concrete forms manufactured by Eco-Block. It’s one of a number of companies producing such concrete forms, although they come in a variety of designs and characteristics.
“Matt contacted us, talking about the ICFs,” says Bill Plunkett, a retired engineer who is executive director of Pulaski County Habitat for Humanity. Habitat is the nonprofit ecumenical Christian organization that builds and sells simple houses to low-income families. The families work alongside volunteers to construct the houses.
Habitat’s headquarters encourage local affiliates to build energy-efficient houses and to recycle or reuse leftover materials.
ICING ON THE CAKE Bell’s offer to sell the forms to Habitat at cost was icing on the cake. “We said we’d try building one to compare the size of energy bills versus [what for us ] would be greater construction costs,” Plunkett says. The home’s owner-to-be agreed to have the new-style walls and to let Habitat know the amount of utility bills. The organization has constructed stick-built houses using the same floor plan and will contact owners to see if they’d also be willing to compare utility bills. Such a comparison can only be informal, Plunkett says, since many factors such as temperature settings will differ. But they’ll have a general idea of homeowners’ mortgage payments and monthly electric bills to see whether the concrete walls will work in their favor.
Here’s more information on the benefits of ICF houses, according to manufacturers (for additional details, check the Insulating Concrete Form Association at www. forms. org and www. smartstructuresdist. com ). With well insulated windows and attic, an ICF house can save 50 percent on energy bills, Bell says. Insulating concrete walls reduce air leakage by 50 percent compared with wood-frame houses. That allows the installation of smaller and less expensive heating and cooling equipment. The houses have a more even temperature throughout the day and night, with virtually no cold spots and fewer drafts.
About one-sixth as much sound gets through an ICF wall compared with an ordinary frame wall. This is an advantage when there are common walls with neighbors or outside noise, as with Vertical. Concrete walls held up under the impact of a 15-pound 2-by-4-inch wood stud “missile” launched at 100 mph, the speed at which flying debris can travel in a 250-mph wind. Wood frame walls couldn’t withstand the impact.
The rigidity of concrete construction can reduce the flex in floors and lessen shifting and vibration from high winds or slamming doors that can occur in frame houses. Concrete-walled houses have survived tornadoes and hurricanes in neighborhoods where wood houses were flattened; when properly reinforced, they should withstand earthquakes.
The walls have up to a fourhour fire rating versus 15 minutes for comparable traditional walls.
Typically, Bell says, an ICF house costs approximately 10 percent more to build than a stick-built house. The concrete walls go up faster, with no need to add layers of insulation or waterproofing. The walls contain no organic materials, so mold and mildew cannot grow there. They contain no formaldehyde or other gases that could affect indoor air quality. Eco-Block says that by weight, its forms are made of 40 percent recycled materials. The basic forms are 4 inches thick or more in 2-inch increments. They can be made to form curves, contours, arches and windows. They can be engineered to any seismic or windload requirements. Furring strips are incorporated in the forms, so any exterior or interior finish can be applied. Space for electrical and plumbing connections are sliced into the foam, so that installation is relatively fast and easy. Windows and door openings also are easy to form.
Buildings using concrete forms may qualify for a Federal Housing Administration energyefficient mortgage. Coming next week:
What’s up with attics ? Find out new ways to spruce up a traditionally undesirable space.
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