Energy Comparisons of Insulated Concrete Forms

ICF Construction Basics

• Insulated concrete forms are a framing technology that combines the insulating benefits of expanded polystyrene panels and the thermal mass benefits of reinforced concrete to create sturdy, energy-efficient homes. Sizes vary by manufacturer, but a typical ICF is an EPS panel that measures out as 4-feet long by 2-feet high by 9-inches thick. Newer generation flat panel ICFs consist of two EPS sheets that are fastened together by a thin steel grid or "tie" to create a 4- to 8-inch opening through which concrete can be poured. The forms click together like Lego blocks and they are commonly used on homes as tall as two stories. The builder then inserts rebar at preselected intervals and pours concrete into the opening. Popular cladding choices include siding, brick and stucco.

ICF Thermal Performance

• The concrete heart of an ICF wall performs quite differently than a wood frame structure that uses fiberglass insulation. Thanks to a principal called thermal mass, the concrete absorbs and stores heat. In the summer, it holds onto outdoor heat until releasing it after sundown when outdoor temperatures drop. In the winter, it holds onto indoor heat rather than allowing it to leak outdoors. The thick EPS panels slow the heat transfer so the ultimate effect of the ICF is to vastly reduce the effect of outdoor heat on indoor air conditioning, and to minimize the loss of indoor heating to the wintry outdoors. As an additional benefit, ICFs are free of the air leaks and thermal bridging common to wood frame or "stick" construction.

Comparing ICF and Wood Frame Houses

• Homes built with insulated concrete forms are significantly more energy efficient than wood frame structures, according to "Energy Use of Concrete Walls with Various Exterior Walls," a 2001 study by The Portland Cement Association. The study noted that the annual cost savings of heating and cooling a wood frame home in a sun-belt city such as Albuquerque came to $182, as of the time of publication. In a four-season city such as Boston, an ICF home would save more than $185 in energy costs as of the time of publication, while ICF homeowners in wintry Winnipeg could expect to save $157. Those savings have likely escalated as energy costs have continued rising.

Comparing ICF to Concrete Block

• Like ICF structures, homes built with concrete masonry units offer the energy saving benefits of a high thermal mass, yet the ICFs outperform CMUs as well. Heating, ventilation and air conditioning savings in sunny Albuquerque amount to $86 as of the time of the study's publication, with $114 projected savings for Boston. In chilly Winnipeg, the yearly savings came to $88 as of the time of publication. Since the biggest difference between CMUs and ICF is the EPS form, it seems apparent that the insulating form itself provides increased benefits to homeowners in hot weather locales.

Evaluating the ICF Advantage

• When working with an experienced builder, the cost of building a new ICF home is typically 2 to 3 percent higher than the cost of building an otherwise identical wood frame home. In regions known for their hot summers, the energy savings should pay back that difference in seven to 10 years, but ICF homes offer additional advantages, too. Homes with ICFs are quieter and less drafty. ICF homes are also a safer choice in hurricane-prone areas because of their poured concrete walls.