Insulated Concrete Forms
Foam blocks called insulated concrete forms or ICFs, offer a style of concrete construction for residential as well as commercial structures. Developed in the 1960s, these hollow blocks are pounds lighter than standard masonry blocks because they are made of expanded polystyrene - similar to the white, insulating foam used for take-out coffee cups. Easy for contractors to cut and assemble, the forms either stack together like giant, interconnecting toy building blocks or come in separate panels connected with plastic ties.
During construction, the stacked forms are filled with concrete and then left in place, becoming a permanent part of the wall assembly and adding a two-inch thick layer of foam insulation to each side of the wall. The lightweight foam forms become excellent insulators and good barriers to air and moisture. Strong enough to hold concrete, they serve well as the backer for interior and exterior finishes.
The two-sided continuous insulation barrier they provide has minimal air leaks and no thermal bridges or insulation gaps common in framed construction, making the building very energy efficient. Reinforcing bars can be added to the hollow areas as the concrete is poured for earthquake safety. Concrete houses also survive high-force winds like hurricanes better than framed structures. The insulated concrete wall can be up to 10 times stronger than a comparable wood frame structure. The thick walls also help to dampen sound and keep out noise and add thermal mass.
Plumbing lines and electrical conduit are usually embedded into the two-inch foam before interior wall coverings are applied. Contractors typically use a hot knife to carve openings in the foam for the piping and cabling. ICFs help to reduce construction waste as well when compared to other building techniques.
Boasting an R-value of 21 and up, foam block walls are so well insulated that manufacturers predict a home's monthly heating and cooling costs can be reduced up to 75 percent. As a result of the added insulation, the size of the home's heating and cooling system could be reduced by as much as 50 percent. The walls are fire, earth quake and termite resistant, and the layers of foam insulation provide excellent soundproofing as well as backing for drywall on the inside and stucco, lap siding or brick on the outside.
According to the EPS Industry Alliance-Insulated Concrete Forms website,
"All ICFs are identical in principle, however the various brands differ widely in the details of their shapes, cavities and component parts.
Block systems have the smallest individual units, ranging from 8 inches x 16 inches (height X length) to 16 inches x 4 feet. A typical ICF block is 10 inches in overall width, with a 6-inch cavity for the concrete. The units are factory-molded with special interlocking edges that allow them to fit together much like plastic children's blocks.
Panel systems have the largest units, ranging from roughly 1 foot by 8 feet to 4 feet x 12 feet. Their foam edges are flat, and interconnection requires attachment of a separate connector or "tie." Panels are assembled into units before setting in place - either on-site or by the local distributor prior to delivery.
Plank systems are similar to panel systems, but generally use smaller faces of foam, ranging in height from 8 inches to 12 inches and in width from 4 feet to 8 feet. The major difference between planks and panels is assembly. The foam planks are outfitted with ties as part of the setting sequence, rather than being pre-assembled into units.
Within these broad categories of ICFs, individual brands vary in their cavity design. Flat wall systems yield a continuous thickness of concrete, like a conventional poured wall. Waffle Grid wall systems have a waffle pattern where the concrete is thicker at some points than others. Screen grid systems have equally spaced horizontal and vertical columns of concrete which are completely encapsulated in foam."
The U.S. Department of Housing and Urban Development notes that
"builders have found that structures using ICF systems had higher costs than conventional construction -- raising the sales price between 1 and 5 percent. Construction crews needed some training but became comfortable with the new techniques by the third form-built house. The houses sold readily, and builders expected to continue using this type of construction."
Some contractors estimate that unusual effects, such as curved walls and frequent corners, can be less expensive to build using insulated concrete forms.
The EPS Industry Alliance-Insulated Concrete Forms lists additional companies and provides more information.