1– Design
“The single most important green design decision is size,” says Wilson. Smaller houses automatically consume fewer resources both during construction and after occupation. “Houses should be sized to work for you every day,” says Sarah Susanka, architect and author of The Not So Big House. Susanka further suggests that we stick to basic shapes. “Simpler forms lose less energy because the ratio of exterior surface area to volume is smaller. Every projection from a house is like a cooling fin.”
Another well-known architect, Peter Pfeiffer of Barley & Pfeiffer Architects in Austin, Texas, applies a Southern take on design. “In cooling climates, solar orientation is the most important design element,” he says, citing a study by the City of Austin’s Energy Star program that showed cooling loads could be cut in half by orienting the long walls of houses east-west, shading south-facing windows, and avoiding expanses of glass on west-facing walls that get the full brunt of the flat afternoon sun.
Even for subdivision lots where the street dictates layout, Pfeiffer says there are still steps you can take. “You can reverse plans to place the garage on the west side of a house. Porches and broad roof overhangs can shade south- and west-facing windows. In cooling-load–dominated climates, a shaded single-pane window will outperform a double-pane, low-E unshaded window. Plant, or don’t cut down in the first place, trees that shade the west side of a house.”
2– Durability
If a house has to be bulldozed in 10 years, it was never green. Durable houses don’t clog landfills and don’t require the energy and resources used in tear-down and replacement.
What’s the key to durability? “Water is probably public enemy one, two, three, and four,” says EBN’s Wilson. “Uncontrolled water rots homes, peels paint, and causes mold.”
Moisture control is a huge focus of building science–inspired components like generous overhangs, proper window and door flashings, and rain-screen walls that allow siding to dry, improve paint durability, and avoid water wicking. In a tightly built house, as houses should be, mistakes that funnel outside water in just aren’t acceptable. The one disadvantage of a tight house is that its walls, roof, and ceilings don’t dry out quickly if they get wet. Normal construction details assume greater importance.
Understanding the demands of your climate is crucial. For example, controlling air and moisture leakage from inside to out not only saves energy, but also can prevent damaging condensation from forming in framing cavities. While there is great debate over the worth and placement of vapor barriers in mixed climates, their use in cold climates is accepted as an important moisture-control element.
Attention to detail–and construction techniques–is another key, and pointed to as a source for many of the moisture-related defects causing so many problems for builders. For example, the common method of simply slashing housewrap in an X at window openings and folding it into the rough openings is outdated and does nothing to keep water from leaking in. These days you have to follow a careful step-by-step flashing, sealing, and installation sequence to ensure proper performance over the life of the building.
Other details frequently skipped can be as basic as omitting housewrap or builder’s felt as a secondary weather barrier. I’ve seen housewrap installed backward (top to bottom). Water that got behind the siding was directed right to the sheathing.
3– Energy Efficiency
Insulation is a job that’s often awarded to the lowest-bidding contractor. From a green perspective, this can be a real mistake. And air sealing–filling the holes where inside air can leak out or outside air can leak in–is at least as important as insulation, because no insulation can achieve its potential if air can leak through it. “Air infiltration must be kept as low as possible,” says Connecticut architect Lindsay Suter. “Air sealing takes discipline and supervision.”
Lots of builders think that air sealing means going around the house after the mechanical trades are finished and filling around where wires, pipes, and ducts pass through walls and top plates with spray foam. This step is important, and foam guns are available to greatly ease this task, but it’s also vital to eliminate big areas that allow inside air access to the thermal envelope. Examples include areas behind bathtubs, showers, and kitchen soffits. These areas should be closed off from the wall behind them with some sort of air barrier–drywall, plywood, ThermoPly, or other type. Recessed ceiling lights are another source of leakage, but new models are available that are air sealed to help control infiltration.
While you’re thinking about HVAC equipment, don’t neglect the ducts. Bill Asdal, a New Jersey contractor who was NAHB’s Remodeler of Year in 2000, advocates both duct sealing with mastic and proper layout. For example, “Don’t run any ducts in unconditioned spaces,” Asdal says.
Pfeiffer claims that “normal air conditioning duct leakage is 20 percent.”
If those ducts are in unconditioned spaces, $20 of every $100 paid for air conditioning is wasted. The importance of properly sealing ducts is easy to see in that light.
If you do an outstanding job of air sealing and insulation, you might qualify for rebates through your state’s Energy Star program. You’ll probably need a blower door test done to measure the home’s tightness and a duct blaster test to measure duct leakage. Those costs might be worthwhile even without state rebates. A blower door test tells you if the house requires mechanical ventilation and dedicated combustion air. And, knowing exactly how tight a house is allows an HVAC contractor to properly size the equipment, which will not only help it perform better but is also often less expensive than larger systems specified without true performance criteria.
As Asdal points out, “It’s the builder’s responsibility to educate trades, spell out expectations, and follow through. Even though the subcontractor might understand your requirements, it’s often his lowest-paid employee doing the work.”
Pfeiffer is a fan of fluorescent lighting. Not only do you get more light for your energy buck from fluorescent (compared to incandescent or halogen), they also produce less heat than incandescents and halogens and can save significantly on cooling loads. So much so, in fact, that Pfeiffer includes replacing incandescent and halogen lights with fluorescents as one of the top five approaches to reducing cooling loads. Fluorescent lights don’t necessarily give off a sickly green light anymore, either. Commonly available lamps with a color temperature of 2,600 to 2,800 kelvin give off light that’s nearly indistinguishable from a cool white incandescent bulb.
Supplying Energy Star–rated appliances is another simple way to cut down energy use. Similar Energy Star–rated appliances can vary in actual consumption, so go one step further and compare annual energy use printed on each appliance’s label, Wilson suggests.