Insulating Concrete Forms Defined
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Rising fuel costs, a greater desire to build for safety and durability, and increasing interest in green building are all contributing to the growth in popularity of a relatively new wall system: insulating concrete forms (ICFs). Although ICF construction has been used in the United States and Canada since the 1960’s, it wasn’t until the 1990’s that the method really caught on. During the past decade, ICF construction has accounted for an ever-increasing share of the overall construction market. Architects and designers throughout the country have found that ICFs meet their design and technical challenges easily and economically, while providing value-added structures to their customers.
What Are ICFs?
At their most basic level, ICFs serve as foam forms for poured concrete walls. The forms remain in place after the concrete has hardened and become part of the wall structure, providing insulation inside and out as well as fastening surfaces for interior and exterior wall finishes. An ICF wall is a solid, flat, steel-reinforced cast-inplace concrete wall, with a concrete thickness of between four and 10 inches that acts as the structural component of the wall assembly.
ICFs are used in commercial and residential construction for exterior and interior, load-bearing and non-load-bearing, and above-grade and below-grade walls. Specific applications include frost walls, basement walls, storm shelters, demising walls, slab-on-grade walls, non-load-bearing walls on post-tensioned floor slabs, and single-story to multi-story walls.
Most ICFs are modular pre-assembled forms that are stacked together in running bond, creating a concrete cavity. A typical ICF block is 10 inches in overall width, with a six-inch cavity for the concrete. The units are factory-molded with special interlocking edges that allow them to fit together, much like plastic children’s blocks. To build ICF walls, installers simply stack the forms to shape the walls, place steel reinforcement bar vertically and horizontally in the center cavity of the wall, and fill it with concrete. This creates monolithic steel-reinforced concrete walls, insulated and ready to finish.
ICFs combine the tremendous strength of steel-reinforced concrete with the insulating properties of expanded polystyrene (EPS) to produce a whole wall, complete with insulation and furring strips. The two EPS panels are held together with strong plastic ties that not only hold the forms together, but also serve as anchors for the steel reinforcement as well as furring strips for the attachment of the finishes.
Advantages of ICF Construction for Homeowners
ICF construction provides many advantages for the homeowner.
Energy savings. The high R-value of the concrete and foam, combined with the thermal mass of the walls and low air infiltration, combine for an effective Rvalue of more than 32. By comparison, a typical wood frame wall has an R-value of 15. The high effective R-value of ICF homes means that energy costs can be reduced by 25% to 50% versus wood- or steel-framed homes, according to the Portland Cement Association (PCA).
Noise reduction and air quality. ICF walls are monolithic, insulated, steel-reinforced concrete, making them virtually airtight. As a result, noise, dust, pollution and allergens are blocked out. ICF walls have achieved Sound Transmission Ratings from 41 to 65, and are so air tight that the industry recommends that an air exchanger be installed to work with the heating and air conditioning systems. That way, only fresh filtered air is circulated throughout the building.
Storm and fire safety. ICF walls have withstood winds up to 200 mph. In 1998, a recently completed ICF home in Washington, Iowa, took a direct hit from an F-3 tornado with winds of more than 200 mph. The owner’s two children, who had taken shelter in the basement, said afterwards that they didn’t even hear the wind or the impact of a large tree that hit the house and did some slight damage to the roof trusses. In addition to the roof damage, a little of the siding blew off and a garage door was damaged. Neighboring wood frame houses were completely destroyed.
ICF walls are fire-resistant as well. The EPS foam won’t burn unless the flame is held continuously against it. As soon as the flame is removed, the forms extinguish themselves. In tests, ICF walls have been shown to resist catching on fire for up to four hours.
Advantages of ICF Construction for Builders and Designers
Generally, traditional builders and designers have been reluctant to accept ICF construction because it was not a wellknown system. However, an increase in consumer demand has forced many of them to take a second look.
Builders. The learning curve on ICF construction is short, especially for anyone with construction experience. Once the crew has some practice, each ICF-built home requires less skilled labor and less total labor than a wood-frame home.
• The same crew installs the whole wall, complete with furring strips and insulation
• Lightweight forms weigh approximately five pounds each, resulting in fewer worker injuries and insurance claims
• Less waste and less jobsite cleanup because cut pieces can be reused in other parts of the wall
Advantages for Architects, Designers and Engineers
Architects, designers and engineers have begun to see ICF construction a solution to design challenges. For example, ICFs were chosen over steel framing on an eight-story condominium project near Portland, Oregon, where dampness and corrosion can be a problem; ICFs were less susceptible because the steel reinforcement bars used are completely encased in concrete. ICFs were chosen over tilt-up for a Marriott exhibit hall with 54- foot high walls in Florida because the building site didn’t offer enough room for tilt-up.
ICF construction has been approved by all the national code agencies as well as major regional code agencies, and AutoCAD details and CSI specifications are available.
Up-front costs for ICF construction exceed those of conventional wood frame construction by a small amount. According to PCA, homebuyers pay approximately 4% more for a concrete home. But over time, the savings on utilities, downsized heating and cooling units, and in some cases insurance, make up the difference.
When architect William Murray of URS Corporation was asked to design the Florida Armed Forces Reserve Center in the St. Petersburg, Florida, area, he was directed to incorporate energy efficiency, green building materials and force protection into the design. “Since September 11th, all military buildings must have force protection built in,” explained Murray. “ICF construction was the most cost effective way to achieve that. Masonry construction would require reinforcement in every block at a cost 25% greater than the cost for ICF construction.” iForm™ by
Reward Wall Systems was the form of choice for the project. Both Murray and Project Manager Stan Shaw of Hunt Construction Group were impressed with the speed of construction, the flexibility in the design and the ease of applying finishes with iForm. Shaw estimated that if concrete block had been specified for the walls, they would have finished at least a month later.