Insulated Concrete Forms
Insulated concrete form construction consists of interlocking modular units -- hollow blocks or panels -- constructed of expanded or extruded polystyrene, stacked in the shape of an exterior wall. Connection ties fasten the inner form to the outer form, similar to conventional concrete forms, and reinforcing steel is placed in the cavity between the inner and outer forms. Concrete is poured into the cavity, and the foam forms stay in place as part of the wall, providing the insulation.
The walls of ICF structures extend from the foundation to the eaves of the house. Insulation values for insulated forms vary according to the material and its thickness, but the values range from R-17 to R-26, compared to R-13 and R-19 for conventional framing methods. ICF construction also has lower air infiltration rates than wood frame construction. There are different types of ICF walls, but generally they have the strength characteristics of reinforced concrete, with high wind and seismic resistance.
Cost Comparison of ICF Walls to Conventional Framing
In 1998, the National Association of Home Builders reported the results of research into ICF costs, concluding that ICF construction costs 2 to 5 percent more than wood frame, with builder's costs 75 cents to $4 higher per square foot floor area than wood construction. NAHB noted that until builders became familiar with the technique, projects could cost 5 to 7 percent more. As a result of higher material and labor costs, sale prices were 3 percent higher. .
Once the house is constructed, ICF buildings generate lower utility bills than wood frame houses, although variations in design details in windows and doors, air sealing, insulation for the ceiling, and HVAC equipment impacts the overall energy efficiency figure. With the energy efficient, airtight construction, heating and cooling equipment is downsized, resulting in lower equipment costs. Homeowners' operational costs are reduced, and because the concrete construction is disaster-resistant, insurance costs may be discounted.