Forms and Function

By Brian Haefs

No matter the region of the United States, inclement weather and extreme temperatures can play havoc with energy bills—as any homeowner will quickly confirm. Without proper insulation, these heating and cooling costs can rise just as quickly as a home’s level of comfort will drop.

According to the Web site of the North American Insulation Manufacturer’s Association, insulation saves 12 times more energy per pound in its first year of use than the energy required to produce it. Implementing a sound insulation system appropriate to a job, then, is a wise investment in a home’s future.

Set in Stone
A highly energy-efficient approach to wall construction, insulated concrete form (ICF) systems make use of an insulating form into which structural concrete is poured. The forms themselves are either pre-molded plastic foamed blocks that interlock or are separate panels connected together with ties. Once the concrete cures, the plastic blocks become a permanent part of the assembly, insulating the inside and outside of the wall.

Although brand specific variations exist, all ICFs have an insulating component that thermally protects the interior and exterior faces of the wall, an interlocking structural assembly that helps hold the forms together, and a poured concrete mass in the middle, in one of three different varieties. “Flat forms” are just that—forms that result in a continuous thickness of concrete wall. “Grid” or “waffle” systems create walls with a variable grid of widths of concrete. “Post and beam” or “screen grid” systems are made up of horizontal and vertical columns of concrete that are completely encased in the insulating material.

The continuous insulation that these forms provide can result in an air-tight barrier that helps protect against thermal infiltration throughout the year. Concrete, by itself has a relatively low resistance to thermal transfer. Surrounding that concrete on both sides with plastic foam helps super-insulate the wall, creating an assembly that resists moisture, insect damage, and heat loss.

And the benefits don’t stop there. ICF systems can also offer resistance to noise penetration, damage from fi res and tornadoes, and corrosion, as well as flexibility in design. Considering ICF’s ease of installation and the light weight of ICF systems, they become a win-win approach for both consumers and professional installers. For all these reasons, ICF systems can be a preferred solution for construction projects that desire highest-end energy performance, such as those measured by LEED, Green Globes, Energy Star or NAHB.

Plastic Foams Used in the Forms ICFs can vary in their make-up. In addition to the flexibility and variability in shape and form of installation, the insulating material that surrounds the poured concrete can differ as well. Insulating compounds vary in their chemical resistance, thermal resistance, thicknesses, and best practices. The savvy builder should be familiar with the differences between available options before determining which insulating plastic composition best satisfi es the needs of a specific job.

EXPANDED POLYSTYRENE
One of the most commonly used foam insulation in the ICF form incorporates expanded polystyrene (EPS)—the same material that makes a typical foam coffee cup. Another form of polystyrene, extruded polystyrene (XPS), is also used. “Most of the ICF market—flat form, waffle grid, screen grid—is EPS, with innovations always coming forth,” says Vera Novak, LEED AP and technical services manager for the Insulating Concrete Form Association (ICFA).

This widespread use of EPS likely stems from its early entrance in the market, and a broad range of benefi ts: During construction and installation, it provides tensile strength and molding adherence to the interlocking ties. It is also easy to cut for custom shapes and quick trimming, and produces little waste. As an insulator, it offers the homeowner limited moisture absorption, steady proven insulation (R-value), a continuous air barrier, and is only superficially affected by ultraviolet (UV) rays. Mason Knowles of Mason Knowles Consulting, LLC suggests another plus for EPS: Ease of material fabrication allows variety in construction applications. “An EPS advantage on prefabricated shaped foam is the ability to have a computer-assisted cutting machine that can create different shapes. That way one company can do many different types of products and not just rely on one type of application.”

POLYURETHANE
Polyurethane (PU), although used less in the “sandwich” configuration in ICF applications, has a higher R-value than EPS at similar thicknesses and can provide an additional degree of energy-efficiency. However, PU does require a higher density, “to have the product meet stress requirements in construction,” explains Kathy Dennis, communications manager at BASF. According to Knowles, PU’s variability of density can be used by installers to their advantage: “You can vary the density and physical properties to achieve higher or lower compression strength, water absorption, insulative value, [and] dimensional stability.”

James Estes, CEO of ThermoBlock, a PU-based ICF form manufacturer, cites PU’s inherent strength and ease of use on-site as two desirable characteristics. “We utilize mechanical cutting devices such as saws, knifes, and routers to work with our product much like you would work with wood, only easier,” explains Estes.

SOY-BASED PRODUCTS Some manufacturers are developing soy-based versions of plastics foams. One such company is EMEGA Biopolymers, LLC, whose primary goals in development were ease of installation and material sustainability. The result is the EMEGA Block, in which soy-based polyurethane is used in conjunction with concrete in molds to form a foam block system that can be manufactured on-site.

Although more research may be necessary before soybased products become more widely accepted into the marketplace, Knowles acknowledges that they may become an alternative to traditional plastic foams. He notes the resulting foam “has indistinguishable properties during the use cycle in a building, from the other foams.” In other words, what the industry may one day be able to offer is an ICF with all the performance advantages of current products and the profi le of an alternative-fuel based compound. Of course, as with any new innovation that intends to reduce our use of fossil fuels, time will tell how these products will impact the environment—and the market—over their life cycles.

Brian Haefs is a freelance writer based in Northern Virginia.

At a press conference in Alexandria, VA, President Obama discussed the economic impacts of energy saving home retrofits at Home Depot.

Learn more about how EPS reduces global warming.

GBS asked the National Association of Home Builders (NAHB) to build several walls, use ASTM standards to measure performance and report the results at ASHRAE ‘s NY Conference.

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