Among the fastest-growing building systems in the U.S., insulating concrete form (ICF) construction offers greater strength, energy efficiency, durability
Among the fastest-growing green building systems in the U.S., insulating concrete form (ICF) construction offers greater strength, energy efficiency, durability and comfort compared to traditional methods, representatives from Omaha, Neb.-based Reward Wall Systems affirm. Although predominantly used in the residential market during the past decade, they add, its use as a forming system for steel-reinforced, poured concrete walls in commercial applications is rapidly expanding.
The Green Building movement has created an environmental awareness among architects, engineers and larger contractors, who increasingly employ systems and products that will enable projects to meet the requirements of the U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED) rating system, a program developed to encourage more environmentally responsible construction. Energy efficiency, air tightness, and recycled content properties enable ICF construction to contribute to a project’s qualification for LEED rating points.
As forms are left in place, becoming part of the wall after concrete placement, an ICF structure gains considerable insulation value as well as integral furring that allows finishes to be anchored directly to the form’s surface. ICFs are used most commonly for exterior, load-bearing walls, according to Reward Wall Systems, but their durability and sound-attenuating properties make them highly suitable for load-bearing and nonload-bearing interior partitions and separation walls as well. After focusing initially on single-family residential applications, ICF producers are now tackling large-scale commercial projects by dint of the code approval achieved for some systems.
LIFE-CYCLE BENEFITS
Because ICF construction yields a monolithic concrete core from footing to top plate between two continuous layers of insulation, through-wall infiltration is virtually eliminated. The system commonly achieves .3 AC/H (air changes per hour) Û or better. When an Omaha, Neb., home Û built with Reward Wall ICF Û was tested for air tightness using the Lawrence-Berkeley blower door method, results of 0.0379 AC/H compared favorably with a super-insulated home (.20 AC/H); good, efficient new construction (.25 AC/H); typical new construction (.35 AC/H); average 1960s construction (.50 AC/H); and, a Victorian-era home (.75 AC/H).
Tight homes use the least energy; and, contrary to common belief, air-tight structures are more easily regulated to enhance indoor air quality. Yet, even in an ICF building, care must be taken in window and door installation to ensure air-tight construction, thereby avoiding leakage to gain the full benefits of the ICF system.
In addition to low infiltration, high-grade insulation (R-18 to R-22) and significant thermal mass provided by ICF construction reduce energy requirements and moderate internal temperature swings to increase occupant comfort. Thermal energy absorbed by the ICF wall is transmitted by conduction, reaching the interior space hours after outside air temperatures have dropped. Thus, the impact of exterior temperature extremes on the interior temperature level is effectively reduced.
The benefits of ICF thermal mass in enhancing R-values and energy performance are more pronounced in hotter climates. The higher R-values attributable to ICFs, therefore, will be achieved only in locales where temperatures reach higher extremes. R-values in colder climates, only slightly improved by thermal mass, are more responsive to reduced air-infiltration rates and the steady state R-value of the foam.
Nevertheless, R-values of ICF structures invariably exceed those of conventional construction. Industry tests have yielded results demonstrating ICF performance equivalent to wood-frame walls insulated to an R-value of 44-plus in Miami, where thermal mass benefits significantly impact ICF performance. In Minneapolis, R-values of 26 or more were noted for ICF construction; in that case, thermal mass benefits were minimal, but the foam’s insulating value and the walls’ monolithic structure reduced air infiltration.
FIRST-COST BENEFITS
Another important factor in green building is construction waste. ICF systems that are reversible Û i.e., matching interlocking teeth top and bottom allow the blocks to be assembled with either side down Û generate less on-site construction waste because smaller parts and pieces more often can be incorporated into the walls. Components can be cut and fit, and remaining pieces used elsewhere. Closer tie spacing also serves to reduce generated waste, as smaller pieces can have ties, making them fully functional in the wall structure.
Of waste that is generated, 100 percent is recyclable. Foam and plastic ties can be reground for use in other products.
The LEED Green Building rating system encourages the use of ICFs containing recycled materials. LEED has formulas for calculating benefits related to either post-consumer or post-industrial recycled material: the former refers to product that is purchased, used and then recycled; the latter includes product, such as manufacturing seconds, that didn’t make it to market and is recycled. More credit is given for use of post-consumer products.
The sustainability of concrete used in ICF construction also promotes green building. On average, cement comprises about 10 to 15 percent of concrete’s overall volume. Its remaining ingredients Û water, air, coarse and fine aggregates Û are locally derived, so cross-country shipping is not required. And, the bulk of concrete is generally limestone, the most abundant mineral on earth.
A study was sponsored by the Canadian government in 1994 to determine the environmental toll of raw material extraction for wood, steel and concrete. Of the three materials, wood harvesting was found to have the most deleterious environmental impact and concrete the least, due to the relatively small scale of quarries and the potential for site restoration.
While carbon dioxide is a byproduct of concrete production, cradle to grave analysis reveals that 90 percent of the compound produced by a home is generated during operation, i.e., heating and cooling. An Inventory Life Cycle analysis performed by Construction Technology Laboratories, Skokie, Ill., indicates that the initial CO2 burden of a concrete home is surpassed in about five to seven years by the additional heating and cooling energy required for a typical wood-frame house.
Additionally, even conservative values touted by the National Association of Home Builders demonstrate that concrete has a much longer life span than either wood or steel. Once it reaches the end of its useful life in a structure, furthermore, concrete is 100 percent recyclable.
Û Reward Wall Systems, www.rewardwalls.com; 800/468-6344