Insulated Concrete Forms
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Insulated concrete forms (ICFs) are made
of expanded polystyrene (EPS) or extruded polystyrene (EXPS). ICFs are
attractive to builders because the light-weight blocks or panels used
to make them are easy to assemble, and they reduce construction time and
transportation costs. The forms are left in place after casting, for both
below-grade and above-grade walls. Currently, more than 23 companies in
North America manufacture and distribute these forms.
Gypsum wallboard or other sheathing must be applied using conventional fastening techniques (nails or screws) that can hold onto both the forms and the concrete. If using adhesive, it must be compatible with the EPS and EXPS foam. It should be noted however, that the Council for American Building Officials (CABO) code does not permit adhesives.
The R-value of an ICF system runs anywhere from R-18 to R-35. The average cost, including labor and materials, is about $5.60/ft2 with the inside wall left unfinished. It is unfinished on the outside and does cost additional for outside finishing. The thermal mass of the wall is 16 Btu/ft2/°F.
The ICF wall system has the potential to have the highest overall R-value of all the foundation systems and can be constructed as high as R-35. Because the forms are designed to resist the load of wet concrete, they must be relatively thick to accommodate that load. The resulting two layers of insulation provide the high R-value.
Foam insulations such as EPS, EXPS, and urethanes tend to be vulnerable to termites, and for this reason, ICFs should be used with caution, unless preventive steps are taken to eliminate the termite threat. Most systems will require some type of fire-resistant wallboard finish on the interior.
ICF systems are gaining in popularity. Homeowners like them because they conserve energy, create a habitable space in the basement, and provide the thermal continuity for the home. Builders like them because they are easy to construct, reducing construction time, and because they have integral fastening strips to facilitate finishing.
Modern technology has reduced the probability of toxicity, VOCs, flame spread, and smoke spread with the latest ICF products, making them a healthier alternative for building than they have been in the past.