Insulated concrete forms (ICF) are leading the way as a forming system and a construction technique for above grade homes. Polystyrene forms are held together by form ties and concrete is placed inside these forms. When the concrete cures, the forms remain in place to serve as insulation and attachment points for interior and exterior finishes. Because steel reinforcement is added, the finished product is substantially stronger and more energy-efficient than conventional wood frame structures.
"Public awareness of ICF concrete homes is now at an all-time high," says Michael Weber, director of residential programs, Portland Cement Association. He estimates that over 15,000 ICF homes were built in the United States in 1999.
Energy savings, protection from the forces of nature, physical security, and quiet comfort are the main emphases. ICF homes offer as much as a 60% reduction in heating and cooling costs when compared with an average wood frame house.
More home developers who build 100 to 200 homes per year, now mostly timber frame construction, are becoming interested.
ICF products are generally classified by assembly: panel, block, or plank. Panel systems are flat sections of expanded polystyrene board connected by plastic wall ties. Block form shapes are either flat, expanded polystyrene side pieces joined together by a wall-tie device or precast blocks that resemble concrete masonry units. Plank shapes are like panel forms with flat surfaces and slots to receive plastic ties.
There are also three basic structural systems inside the walls: flat panel, waffle, and screen. Flat panel systems resemble standard cast-in-place concrete walls. Waffle systems create a grid of horizontal and vertical concrete cylinders, with a web of concrete filling the openings between the cylinders. Screen systems also use the horizontal and vertical cylinders but without the thin web. The foam extends through the form, creating a structural core that looks like a screen.
ICF units use two types of polystyrene foam: (EPS) EPS for molded block form products and XPS for panel and plank applications. The biggest difference between the two is compressive and tensile strength.
Each company has proprietary wall ties and foam pieces. When you decide to use one manufactured system, you commit to using all the elements of that system.
ICF product is said to be eight times safer in seismic events than wood frame buildings.
General guidelines for concrete mixes are presented here.
Many homeowners choose to live in ICF homes for comfort and safety—not because they are saving money on the purchase. The increased cost of a home, however, is paid back many times over with savings on energy costs and reduced maintenance and insurance costs.
Energy has become important due to its increasing cost and the greenhouse effect that combustion gases cause. The insulation value of ICF systems is R-17 to R-22—an increase of 65% over traditional wood frame construction. More important, however, is "energy performance," which relates to the "tightness" of a structure or the amount of conditioned air that leaks from the structure. The amount of heating and cooling energy saved depends on the dwelling size and the climate of its location.