Energy Equation
Do your houses leak energy like this one? One way to ensure energy efficiency is to build using a high-performance strategy. These five minimum requirements can maximize returns for you and your buyers.
Launch Slideshow
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.
Roof Roof
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.
Seal of Approval
In the eyes of some experts, blocking air movement is the most important energy move builders can make.
"Air movement is a big issue for us," says C.R. Herro, national vice president of environmental affairs at Scottsdale, Ariz.–based Meritage Homes, which claims to be the only top 10 builder that offers 100 percent Energy Star–qualified homes. Air leakage, especially random air movement through building cavities, can account for 30 percent or more of a home's heating and cooling costs, according to the DOE.
The first line of defense is to use caulk to seal cracks, gaps, and joints, especially at the connections and elements that penetrate the building envelope. Couple that with an air barrier that has been taped at the seams—which improves the performance by 20 percent—and you have a pretty air-tight, inexpensive building envelope. But the efficiency of this barrier is heavily dependent on how well the shell is sealed and the wrap is installed and taped.
The same performance may be achieved with more reliability by using one of the whole-home air sealing and insulation systems that manufacturers such as Owens Corning or Knauf have introduced recently. Another, even more effective approach—which also happens to be the priciest—is to use spray foam insulation. This approach may be three times more expensive than other methods, but green building consultants say it leaves little to chance. Plus, with an R-value approaching 6 per inch, your walls will be well insulated.
Insulation Nation
Every builder has a preference when it comes to insulation. Most swear by inexpensive batt insulation, but others say the product performs well only when it's properly installed. "I never recommend batt," Edminster says. "It's almost impossible to do a good job installing batt insulation. It's a good idea in theory, but in practice it's a nightmare to do well and certainly not fast."
At the other extreme, foam insulates very well by completely sealing wall cavities. But it is often highly impractical in production housing because of its cost. For that reason, some builders have resorted to a hybrid system that includes batt insulation, good air sealing, and, as a back up (and to stop thermal bridging), rigid foam board on the home exterior.
Whatever insulation you choose, Edminster says, "it should touch on all six sides (full contact) of the wall cavity." Also, the DOE says it's important to exceed local building codes that probably only include minimum requirements that likely will not result in a truly energy-efficient and high-performance home.
Windows on the World
Today nearly every builder selects insulated, low-E, Energy Star windows. But it is important to think about fenestration in a broader context, too. Window placement is just as important as window performance. Unfortunately, that may be dictated by how subdivisions are planned. Even so, exposing windows to direct sunlight is unacceptable, Binkley cautions. Thoughtful placement can do more to cut down on heat gain than a low-E coating. And make sure that windows that do have some exposure to the sun also have appropriate overhangs or protection devices such as trees or exterior shades. Postgreen prefers fiberglass windows for their durability and good looks, and the company avoids certain types of styles. "We use casement windows because they give you a tighter seal [when they are closed], and we avoid using double-hungs or products with a lot of framing," Ludeman explains. "The casement gives you more insulated glass and less framing that can cause thermal bridging." Yes, casement windows do cost more, he says, but to balance it out, the company also uses a combination of operable and fixed glass openings—about 30 percent to 40 percent—that cuts costs significantly.
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Scott's Contracting
scottscontracting@gmail.com
http://stlouisrenewableenergy.blogspot.com
