Screenwriter William Goldman once said that in Hollywood, “nobody knows nothing.” What he meant, of course, was that no one knows for sure how to make a successful movie or even predict if one will be a financial hit.
The same, it could be said, goes for building energy-efficient homes. Varying certification requirements, unclear definitions of green building, and competing scientific theories can, and do, lead to confusion and frustration among builders. No one seems to know just the right combination of features that will hit the sweet spot of energy efficiency and profitability.
In that spirit, we offer five basics of energy-efficient design and construction that make sense to follow no matter what type of house you’re building. And techniques that lower utility bills—sealing air leaks, using high-performance windows, and right-sizing HVAC systems—shouldn’t be ignored in any economic climate.
Complicating the picture, builders need to look at each home in the context of its local market, price point, and the availability of products and systems. “It’s always best to design for your local climate,” says Ed Binkley, the principal of Ed Binkley Design in Oviedo, Fla. “This is the least expensive” way to go, he adds.
The size of the home is another key variable, says Ann V. Edminster. “I’m a provocateur, so I ask how small a house do you want to build,” says the principal and owner of Design AVEnues, a green building consulting firm in Pacifica, Calif. Edminster always recommends simple styles and more consolidated roof lines. Complexity, she says, “adds to the potential for mistakes in insulating, air sealing, and flashing.”
Even builders who follow the basics must often make difficult trade-offs. Specifying solar panels for energy independence may seem like a good idea, but if the budget is tight, the high premium for an array might be better spent on upgraded insulation, good air sealing, or a high-efficiency air conditioner. Tough choices, but no one said this would be easy.
The following five recommendations are the bare minimum, even with a tight budget. If more money is available, don’t forget other important features such as low-energy lighting, water conservation, and good indoor air quality.
The roof is not only the first line of defense against the elements; it is absolutely critical to the energy performance of the home. "Most of your energy loss occurs through the roof," says Binkley. One of the most routine construction methods is a vented roof with a sealed and insulated attic space. The devil, as always, is in the details—in this case creating a good seal between the conditioned space and the attic. Depending on the climate, insulating just below the roof deck—with blown-in foam, for example—might be an easier and higher-performing method, though it may also be more expensive to execute. "We go back and forth on the issue [of a vented attic versus a non-vented]," says Chad Ludeman, president of Philadelphia-based green builder Postgreen, which specializes in eco-friendly homes. Other options include using rigid foam board or radiant barrier sheathing on the exterior of the roof deck, which consultants (and the Energy Department) say cuts down on heat gain in the attic. The bottom line is that you need to pay particular attention to the roof and attic if you want your homes to be comfortable as well as energy efficient.
Walls of Fame
Walls may be the next most important factor in a home’s energy efficiency. Though most builders use 4-inch studs spaced 16 inches on center, builders of energy-efficient homes in colder climates have upgraded to 6-inch studs spaced at 24 inches. This creates a deeper wall cavity that leaves more room for insulation and raises the total R-value of the wall system. The key in any climate, however, is to completely seal the wall cavity. Though any kind of insulation will work as long as its installed properly, some builders prefer sprayed-in insulation, such as foam or cellulose, despite their higher cost.
Postgreen is so serious about its walls that it often builds two layers instead of one, a technique that seems like overkill but results in a high-performance shell. "We build two 2x4 walls with a 2-inch space between the two," Ludeman says. "It allows us to get the insulation we want and allows us to get rid of the thermal bridging."
On the exterior, the company uses an OSB-based sheathing system with a built-in protective overlay, topped by a continuous exterior layer of R-10 rigid foam board. Downsizing HVAC system requirements pays for the added materials. This "could just possibly be the most affordable wall assembly that achieves maximum R-value and minimum thermal bridging," the builder writes on its blog, 100KHouse.
Learn more about markets featured in this article: Philadelphia, PA.