Icf Questions: What Is An Insulated Concrete Form?

The ICF system represents a reasonable alternative to traditional wood framing.

Most American homes are constructed with a wood "stick-framing" wall system built on top of a traditional poured-concrete foundation wall. This is a tried-and-true building system, but it's important to realize that other alternatives do exist, each with its own benefits. One popular construction alternative is the insulated concrete form, or ICF.

There are many different brands and systems of ICFs, but all work in a similar fashion and provide a concrete core surrounded by rigid insulation. Some consist of blocks that fit together and interlock to form a tight seal, while others come in a panel design; these are typically held together with a tie system. Their structural strength is acquired when they are filled with concrete, which is further reinforced with steel rebar. This reinforcing system works just like a traditional poured-concrete foundation wall.

ICFs are made of expanded polystyrene, which is highly insulative. Their R-values (a measure of the effectiveness of insulation) can often exceed R-30. They do not have the air-leakage problems of wood framing, and the concrete provides a continuous thermal mass which is absent in wood framing. These characteristics often allow homes built with ICFs to be eligible for EnergyStar approval ratings; the costs of heating and cooling can be reduced by over two-thirds over the life of a home.

ICFs have become more popular recently as the cost of other building materials has increased, although they have been in use for decades. Their higher initial costs are offset by the fact that they combine different home-building stages; these stages are normally considered separate, but the ICF system compresses them into a single stage. In a stick-built home, the wood members are assembled by framing crews, and insulated with batt insulation. Then, the home is wrapped with a moisture-proof membrane. The distinct advantage of the ICF system is that it contains all those stages in a single construction element.

ICFs are versatile and economical in that each part provides multiple benefits. In addition to insulating the home effectively, the polystyrene provides significant soundproofing and is both moisture and insect resistant. It also provides an excellent substructure for gypsum-board (drywall) or paneling on interior finishes, and for sheathing, siding or stucco systems on the exterior. The concrete core adds significant shear strength, and therefore provides earthquake and tornado protection. ICF systems are typically quite flexible, as most come in a variety of sizes and configurations to suit almost any construction application. Some can even be field-cut with a saw to meet custom dimensions, and nearly all contain pre-made channels for electrical and plumbing runs.

Although ICFs have an initial cost that is several percentage points higher than traditional stick framing, their advantages make them an option worthy of consideration for most homebuilders. The substantial energy savings gained over the life of the home will pay back the higher initial cost quickly, and lower maintenance expenses can be a major factor as well. Insurance companies look very favorably upon the seismic and fire resistance of the system; in some parts of the country, they are often willing to consider lower homeowner's-insurance premiums for ICF-constructed homes.

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