The term “high performance” likely conjures up an image of a car, one that's sleek and speedy, with an extremely powerful engine. The expectations surrounding such cars are high, which is why their allure is so strong.

“High performance” is a descriptor now being used in the home building industry, as well, and its proponents hope the term will evolve to the point where it evokes similar expectations. Like their vehicular counterparts, high-performance homes aren't characterized as much by their form as they are by their function.

“A high-performance home is one that has good measured indoor air quality and is comfortable [temperature-wise],” says Timothy Locke, a principal at Fair Oaks, Calif.–based Western Technical Associates, a building science consulting firm. “It has the same temperature everywhere in the house and has low energy bills.” Such a house, says Locke, may cost its owners as little as $400 per year in energy bills.

Architect Joseph Vigil, president of architectural firm VaST in Boulder, Colo., echoes Locke's description. He defines a high-performance home as one “that is very tight and doesn't lose a lot of energy through the walls and has a high-efficiency cooling system.”

In short, a high-performance home is as energy efficient as a high-performance car is powerful and fast. It has features that are vastly superior to the average home—or even one built to model energy codes: a well insulated shell, tight construction, energy-efficient windows and HVAC system, and clean indoor air.

IS IT GREEN?
Builders and consultants agree that high-performance homes by definition reduce fossil-fuel usage and keep their inhabitants comfortable, which many claim qualifies these homes for green status. However, Vigil says, and many others agree, that high performance is only one component of a three-legged, green, home design stool that building pros should consider.

“[High-performance building] usually has to do with energy, but it's not necessarily about green,” Vigil explains. Green construction, he says, is broken down into three areas: being mindful of the natural environment, building to high-performance standards, and being socially conscious. “It's possible to incorporate all three in a house, but they may not go hand in hand.”

Vigil says, for example, that concrete is considered by many people to be a green material—especially if it contains fly-ash waste from power plants—but it takes a lot of energy to produce the material. The same goes for solar technology.

It's true that a fully sustainable or green house considers many issues, from the way materials are sourced and manufactured to life-cycle analysis; converting your company to one that does fully sustainable houses is a serious undertaking. But interested builders must start somewhere, and because energy efficiency often accounts for half of the points in many green building programs, a high-performing, energy-efficient home is a good place to begin.

Building high-performance homes that have a strong emphasis on energy efficiency has been the strategy of builder Chuck Miller, president of Hidden Springs, Idaho–based Chuck Miller Construction, which builds about 12 high-performance homes a year. “My buyers pay about two-thirds less than their neighbors to heat and cool their homes,” Miller says. “They pay about $1,200 [a year] for gas and electric, while their neighbors pay about $3,600.”

So what exactly does high-performance construction entail, and how do you go about building a durable house that uses less energy?

SHELL GAME
House orientation is the first thing a builder should look at when attempting to increase energy efficiency in his homes. Situating a house to take advantage of sun and shade can make an enormous difference in the energy required for heating and cooling. Then, leaky walls, inadequate insulation, improperly flashed windows and doors, thermal conductivity, inadequate housewrap, and a host of similar mistakes bear investigation as causes of energy-porous construction.

Creating a tight shell and building better wall assemblies are top priorities in constructing a high-performance house. First steps in that direction include two interrelated areas, insulation and wall framing.

Generally, say building scientists, builders use too much wood in their walls. Miller, who builds his homes to the Department of Energy's Building America standards, uses 2x6 studs set 24 inches apart instead of 2x4s set 16 inches apart. This simple move accomplishes several things: It decreases the amount of wood in the wall but creates a stronger house, and it reduces heat loss and gain due to thermal bridging through the studs. But more important, less wood in the wall assembly frees up space for the builder to use more insulation, especially the type that completely fills the wall cavity. Using this type of insulation might cost more money, but it offers better performance. “We generally use cellulose insulation and use Icynene [sprayed foam] occasionally,” says Pam Sessions of Hedgewood Properties, a Cumming, Ga.–based company that builds to EarthCraft House green building standards.

Completely filling the wall prevents air from seeping into the conditioned spaces, says Locke, so the manner in which the insulation is installed is very important. “Small errors in insulation installation make a big difference in the overall performance,” he says. For example, if the installer leaves voids or gaps, or if the insulation slumps just a little, an R-13 product may yield only an R-6 performance.

A gap in the insulation is only one of the areas that can affect the performance of a house. A typical house, new or existing, has myriad areas where airflow and heat loss can occur. Areas to focus on include gaps in framing and places where the shell has been penetrated, such as around electrical wiring and vent pipes. Other trouble spots include the transition points from the basement wall to the first floor and from the second floor to the roof; chimneys; and dormers, says Peter Yost, a principal at 3-D Building Solutions, a high-performance–building consulting firm with offices in Brattleboro, Vt., and Bexley, Ohio. Sealing these gaps prevents air infiltration, and as an added bonus, it also stops moisture intrusion, curbing mold growth. When building a tight shell, Yost says, “you have to pay attention to moisture flow as much as you pay attention to energy flow.”

Other key steps include properly caulking and flashing all four sides of the high-efficiency windows you're (hopefully) using, installing adequate housewrap that allows the house to breathe, and using a properly installed drainage plane. “Drainage planes are water-repellent materials (building paper, housewrap, sheet membranes, etc.) that are located behind the cladding and are designed and constructed to drain water that passes through the cladding,” writes Joseph Lstiburek, a principal of Building Science Corp. in Westford, Mass., on his company's Web site. Controlling the flow of rainwater is the single most important factor in the design and construction of durable buildings and in controlling mold, he believes.

But even if you use advanced framing and reduce the amount of wood in your walls, heat conduction can still occur through the studs. Chris Briley, principal of Green Design Studio in Yarmouth, Maine, minimizes this thermal bridging by using horizontal straps. He places the straps between the drywall and the studs on the interior and between the studs and the exterior sheathing. Miller, meanwhile, uses a double air-barrier system consisting of ¾-inch polyisocyanurate foam sheathing installed over the structural sheathing to reduce heat loss and heat gain.

A MODEL SYSTEM
The down side of tighter building envelopes is that they can result in a higher risk of poor indoor air quality and mold growth than in previous eras. In the old days, the typical house had adequate fresh air and few, if any, mold problems. Unfortunately, that same house was also drafty and wasted tons of energy. Today we know better: A tight shell is an improvement for energy efficiency, but the key to indoor air quality is controlling how you bring fresh air into the house. The best way to do this is with an effective HVAC system.

The reality is that today's HVAC systems are poorly designed, building scientists say. As a result, most people are uncomfortable in their homes and have to run their systems longer to get comfortable; typical ducts leak up to 20 percent of the air they move; and the systems bring in an inadequate amount of fresh air and offer poor humidity control and filtration. In addition, most are oversized.

“An ineffectively designed duct system is a big problem,” Locke says. “People just slap up the system without checking how much air it throws or how many cubic feet per minute the system handles.”

To combat this lack of precision, consultants say, builders should perform energy modeling on their HVAC systems and properly size their units. Oversized units don't stay on long enough, and the bursts of warm or cold air can deceive a thermostat into shutting off the system before the house is adequately conditioned. An adequately sized unit also improves the humidity levels in the home and costs significantly less.

Sealed ducts, meanwhile, improve the indoor air quality and comfort of the home, lower energy bills, and allow builders to lower equipment costs. “We seal our ducts and do duct-blast testing to ensure proper operation,” says Sessions.

Miller says his company installs ductwork in conditioned spaces only. “Leaky return ducts can draw air out of unconditioned spaces that is hotter or colder than the return air, thus increasing loads on heating and cooling systems,” the company says. Moreover, return ducts in attics, unfinished basements, crawl spaces, and garages can also draw pollutants and contaminate indoor air.

“We use an energy recovery ventilation system,” Briley notes. “It senses carbon dioxide and humidity and activates [itself in response]. It exhausts stale air and tempers and introduces warm, humidified air to the house. You essentially control the leakiness of the house.”

BREATHE EASY
Now that your shell is tight and you have designed an efficient HVAC system, the last thing you want to do is pollute your interior air with off-gassing building products.

Thankfully, manufacturers have made it easier for builders to avoid toxin-laden products. Low volatile organic compound (VOC) paints, stains, and finishes are widely available from such companies as Sherwin-Williams, Benjamin Moore, and Rodda Paint. Columbia Forest Products offers formaldehyde-free veneer paneling for cabinetry and furniture, and Johns Manville now makes a formaldehyde-free insulation. A variety of materials—bamboo from Teragren, cork from Expanko, linoleum from Forbo—also makes it easy to install a durable, sustainable floor.

Making sure the interior air is free of volatile organic compounds is part of a larger, important effort to make sure high-performance homes are healthy and safe for homeowners, says Jay Hall, director of research at Building Knowledge. The company, a Minneapolis-based building science consulting firm, works with builders to get them up to speed with energy-efficient techniques.

“We figure out where the builder is and help them figure out the logical next step to address issues in an efficient way,” Hall explains. “It's a big leap to get there all at once, because there are a lot of [points] to work out, which is why we promote an incremental approach.” Part of that incremental approach includes stressing health and safety issues such as indoor air quality, combustion gas, and radon. The company has a list of priority areas it addresses when working with builders.

After conducting a baseline assessment, Building Knowledge's priorities for the builder include combustion safety, water management, the thermal shell, and air tightness. Then they move on to crawl-space design improvements, HVAC redesign, increased duct tightness and relocation, and ventilation issues.

BETTER ALL AROUND
A high-performance home will be safer to live in and will have lower utility bills than a typical home, but it will also be a better house all around, says Mike Kerwin, a partner with Lorax Development, a six-year-old San Francisco–based company that builds green houses. “To me, high performance relates to energy efficiency and quality of materials, and how a home will perform over time,” he says. “For the home buyer, this means a certain peace of mind, fewer maintenance costs, and added value down the road.”

All of these recommendations merely scratch the surface of the research conducted by building scientists, green building programs, and other experts, and they serve purely as a starting point for building high-performance homes. For example, a high-performance home in a very cold climate will likely be built differently from one in a hot and humid area, so builders should take regional conditions into consideration and build accordingly.

Experts agree, however, on one step that all builders should follow, no matter what high-performance construction methods they use or where they build: Obtain third-party certification. Prescriptive methods say one thing about how a product will perform in the field, but the only way to know for sure whether something was installed correctly to achieve high performance is by having a third party examine it. It is not as difficult as it was in years past to have your homes certified by a third party. All across the nation, trained consultants and engineers have been approved to test homes to make sure they are performing as efficiently as they should.

Indeed, installation is where the rubber meets the road for the testers, Locke says. “Installation isn't always done correctly, so most homes aren't high performance,” he says. “There's a cascade effect [contributing to subpar performance] because people don't look at how these things work together.”