Are You Overheating (or Cooling) Your ICF Home?
A 'Systems Approach' Can Maximize Its Energy-Savings Potential
The market is red-hot for concrete homes and likely to gain even more steam as energy prices continue to escalate with no end in sight. The most recent residential market data compiled by the National Association of Home Builders (NAHB) show that 16.1% of all new single-family homes built in 2003 used a concrete wall system, with the percentage forecasted to increase to 25% in 2005. In 1993, the market share for concrete homes was a humble 3%.
Certainly, one of the main reasons for this double-digit growth is the superior energy efficiency of concrete homes when compared with typical wood-frame construction. Building exterior walls using insulating concrete forms (ICFs) or other concrete wall systems can potentially save hundreds of dollars annually in heating and cooling expenses. But constructing an energy-efficient thermal envelope doesn't always guarantee rock-bottom utility costs, contends Richard Rue of EnergyWise Structures, Arlington, Texas.
"It's sad how many frustrated people we talk to who aren't getting the energy savings they expected. They contact us and say: 'I built an ICF home because I thought it would be the panacea and automatically ensure low utility bills.' They've got part of the picture, but they don't have it all," says Rue.
To complete the picture, he stresses the importance of taking a "systems approach" when designing and building an ICF home (see Rue's other strategies for achieving optimum energy savings). As part of a systems, or whole-house, approach, the HVAC system is engineered to work in harmony with the structure's thermal envelope and local climate conditions. This can assure the homeowner of three important benefits:
"It all starts with proper engineering of the entire package: the mechanical systems, doors and windows, the insulation, and caulking to prevent air infiltration," says Rue. "If you take the systems approach to building an ICF home, you can put your thermostat at virtually any temperature, and once the temperature stabilizes, it will take very little energy to maintain it." says Rue.
Common mistakes that eat into energy savings Because concrete homes are so inherently energy efficient, owners can easily get by with smaller-capacity heating and cooling equipment. Yet many HVAC contractors are unfamiliar with the superior thermal qualities of concrete homes and end up installing oversized equipment that not only carries a higher price tag, but also costs more to operate.
Another common mistake is to mix and match heating and cooling equipment, using components made by different manufacturers. Like a precision-engineered automobile, the HVAC system will operate much more efficiently if all the equipment is compatible. Variable-speed systems also deliver better energy performance than single-speed equipment because they automatically adjust the flow of heated or cooled air to the desired comfort level. These systems will typically run longer but at lower speeds, which provides better humidity control while reducing operating costs.
A big blunder Rue frequently encounters is the installation of air-to-air heat exchangers in concrete homes, based on the flawed thinking that since concrete homes are more airtight, bringing in outdoor air is necessary to maintain good indoor air quality. "If you install an air-to-air heat exchanger, especially in hot and humid or polluted climates, you're just asking for trouble," says Rue. "Why bring in additional outside moisture or polluted air? There's no need. Although ICF walls may be airtight, the average house will have at least a 10% to 20% window-to-wall ratio. There's enough leakage through windows alone to make up for any air exhausted through bathroom or kitchen venting."
Choosing the right attic insulation is another key factor in the energy performance of a concrete home—and in reducing the overall operating costs of HVAC equipment. Unfortunately, most builders subscribe to the "R-value myth" and don't always make the best choice, says Rue. Comparing the R-values, which are determined under laboratory conditions, can be deceiving, he explains. These values are based primarily on the ability of a material to resist the conduction of heat and don't fully account for air infiltration through the insulation system. Controlling this air movement is vital to ensuring thermal comfort and minimizing energy use. Spun fiberglass is an example of an insulation material that boasts high R-values but has poor air-infiltration control properties. Instead, Rue recommends the use of sprayed-foam insulation in the attic because it's an excellent infiltration barrier.
Who to turn to for help
"When you use a licensed mechanical engineer, you have someone to turn to who's responsible for correct sizing of the HVAC system. The engineer should get involved from Day 1," says Rue.
How do you find a qualified mechanical engineer, particularly one that specializes in foam-insulated concrete home systems? Rue recommends asking the manufacturer or distributor of the ICF wall system. "People who are selling you ultra-energy-efficient products should take responsibility for giving you the resources you need to achieve successful results," he says.
You should also insist on an inspection of the home, to ensure that the design and engineering is done properly. EnergyWise is developing procedures for videotaped inspections of every job, and plans to send copies to the homeowner and builder as a visual record.
"We can do all this—the engineering and inspection—for less than 35 cents per square foot. If you're building a 3,000-square-foot house, you can get a mechanical system that's professionally engineered and inspected—along with a guarantee of lower utility costs—for about $1,000," says Rue.
A wise investment, indeed, in this age of soaring energy costs.
Anne Balogh writes feature articles each month for The Concrete Network ( www.concretenetwork.com). She is a freelance writer based in Glen Ellyn, Ill., and a former editor of Concrete Construction magazine.