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Design the Crucial Factor in Effective Green Building
Instead of worrying about offbeat construction materials and techniques, home builders interested in pursuing green home building opportunities should start by considering basic designs — many of which have been around for ages — that will promote the peak performance of the house, Peter Pfeiffer, of Barley & Pfeiffer Architects in Austin, Texas, told the NAHB National Green Building Conference in St. Louis last month.
“This is not about bamboo floors and geothermal heat pumps,” Pfeiffer said, “but the first decisions we make even before we begin building. Let’s make some smart design decisions first….Green building is less about finding materials and more about the appropriateness of the design.”
The first principle of green building, he said, is making sure that the building relates well to its site. “Orienting the house correctly can save more than a photovoltaic system on the roof,” he said.
From the outset, green builders should also be working with their clients to educate and manage their expectations. For instance, ask a middle-aged client who wants the master bedroom downstairs to avoid a flight of stairs if they really expect to be living in the house when they are 75. Because if they don’t, it makes more sense to locate all of the bedrooms upstairs so that the first floor doesn’t need to be air conditioned at night, cutting energy bills in half.
Persuade your client that they want to avoid an air conditioning system that has the capacity to cool the house down to 72 degrees on the relatively few occasions when they have 25 people over because overcapacity can cause mold to grow within the ducts and elsewhere in the home, leading to poor indoor air quality and possible health problems.
Explain that excessively large homes may not be as comfortable to live in or that a 12-foot ceiling will use one-third more energy to heat and cool. And try to get away from the traditional way of looking at the value of a home on a cost-per-square-foot basis. “The industry has started judging homes on price per square foot to the point of absurdity,” Pfeiffer said. “When you look at the cost of a sport coat, do you consider how much it costs per square inch?”
“In today’s market,” he added, “people are looking for something that’s better thought-out and better performing.”
In thinking through a project before it gets going, builders should look for energy conservation first before they pursue energy production. “Energy conservation provides the most bang for the buck,” he said, “and it is a lot less expensive than solar collectors.”
Orientation of the home is extremely important and often overlooked. Streets should travel east and west as much as possible so that the majority of the building lots can have either a north — or south — facing front and rear.
Where air conditioning is used extensively throughout the year, the home should be oriented to avoid exposure to the afternoon sun, and windows facing west should be minimized. Dark roofs are also undesirable because they absorb the heat of the sun.
Pfeiffer presented a long list of basic recommendations for improving indoor energy efficiency and comfort. Among them:
- “The placement of air conditioning and heating equipment shouldn’t be an afterthought.” Locating it next to the master bath and kitchen can reduce duct runs. With proper windows and shading, most houses should require no more than one ton of cooling capacity for every 650 square feet of living area; “850 square feet/ton is now very attainable and should be the goal of a well-designed and built residence.”
- Use overhangs to shade windows on the east, south and especially the west from the sun. Double-pane “low-E” windows are not a substitute for proper shading and solar control. Available through Ball State University’s Center for Energy Research, Education and Service, the Sun Angle Calculator enables builders to determine what size overhang they need. Overhangs help keep the sun off of paint jobs, and keep windows cleaner because they don’t get wet during rain storms. “Houses with small overhangs don’t last,” he said. Doors and windows will last four times longer when water is kept off of them.
- A radiant barrier on the underside of the roof, such as LP’s “Tech Shield,” will substantially reduce heat gain through the roof — reducing air conditioning bills, enhancing occupant comfort and extending the weeks in a year a home doesn’t need air conditioning. Contrary to myth, radiant barriers do not lead to the deterioration of roof shingles. “Radiant barriers do need to be installed in conjunction with an air space and will not provide benefit where in direct contact with another building material.” Sealed attics and radiant barriers also make it less of a problem to run air conditioning ducts in the attic. “However, it is always best to run ducts in a conditioned or semi-conditioned space, such as ceiling furr downs or in an unvented attic.”
- “Ventilating an attic can cause moisture and humidity problems in areas of high humidity — and lead to higher energy bills. Sealing the attic and ventilating a continuous air space immediately below the roof decking, not the attic, is better.”
- To keep humidity from infiltrating the wall cavity, install a moisture and vapor retarder on the warm, or more humid, side of the wall. “In the North, this is the inside surface (unless you are in an area where air conditioning is used a lot of the year); in the southern United States this is the outside surface of exterior walls….” Typically, when you are air conditioning a house, walls dry ‘out’ to the interior because the a/c system draws moisture out of the air. Spray foam insulation is particularly good in areas where significant air conditioning and heating loads exist because it is a safe vapor retarder that works appropriately in the summer and the winter.”
- Look for siding that sheds water to minimize the water the cladding absorbs. Masonry and stucco absorb water; and the sun heating up a wet wall will drive moisture right into the house.
- 30# ASTM building felt in conjunction with a commercial-grade building wrap that is well taped makes for a good weather barrier system. “Remember, you want to create a raincoat underneath the wall cladding because houses aren’t perfect and cracks will occur that let things in that you still want to keep out of the house.”
- Do not use vapor barriers on the inside surface of walls — including vinyl wall coverings, in buildings where air conditioning is used for a significant part of the year. “Improperly placed vapor barriers can trap moisture in walls — leading to serious mold problems.”
- “Go easy on the amount of recessed cans (even the so-called ‘air-tight’ ones) that puncture the thermal envelope of the building. They are counterproductive to reducing infiltration of outside air. Try to restrict unnecessary light switches and electric boxes on exterior walls — they, too, puncture the thermal envelope.”
- A vented crawl space can create more moisture and humidity problems than it solves. “We don’t recommend venting them unless there is a known source of ground water under the building that cannot be controlled otherwise.”
- “You have to build an air-tight house.”
- To improve indoor air quality, “don’t pollute the home in the first place rather than diluting the pollution.” Use low-VOC (Volatile Organic Compounds) latex paints on the interior. “Avoid high-sheen or glossy wall paint on the interior surface or exterior walls, where it could create a vapor barrier on the wrong side of the wall.” Air out carpeting for a day or two before installation. Detach or separate the garage from the house; in addition to the car, fertilizer, insecticides and other chemicals stored there can create fumes. “Sheetrock is not a vapor barrier. At least use foam insulation.”
- Avoid chemical treatments for termites and other insects. “They don’t last, lead to occupant health problems and pollute the underlying ground water. Consider sand barriers or stainless steel screen barriers such as TermiMesh in and around the foundation for termite control.” Also, the frame of the structure can be sprayed with Timbor, a natural brine solution that makes the entire frame insect-resistant.
- “Install outside venting exhaust fans in all bathrooms, kitchens and other rooms where there may be a lot of internal moisture generation. BUT be careful not to draw so much air out that you create a negative pressure in the home or building because that will exacerbate the infiltration of unwanted air.”
- “Keeping humidity levels low is an important part of controlling indoor air quality. Front-loading clothes washers impart less humidity into a home because they are sealed during operation. Indoor air humidity should be kept at 40% to 50%."
- “Leaky ducts rob energy efficiency and are a bigger problem than low-efficiency air conditioners. They can cause depressurization of a home, inviting outside air and humidity into the home from unknown and unwanted sources, leading to serious indoor air quality problems and possibly mold.”
- Fluorescent lamps — especially the thin T2, T5 and T8 types and the new compact fluorescents — provide superior light quality and provide a wide range of color correctness without the heat of incandescent and halogen lamps. They also last longer.
- “Proper day lighting, especially indirect daylight from high windows, can make for substantial energy savings and an enhanced indoor environment. (Clerestory windows do this well; and if operable, can be used to naturally siphon heat out of the space below in the spring and fall.)
- “Avoid oversized (75-gallon and larger) water heaters. They generally don’t produce heat as efficiently as smaller ones because they are exempt from the federal energy conservation guidelines. A good high output 50-gallon gas unit will produce the same amount of hot water, enough for most large homes with oversized master bath tubs, more efficiently. A simple backflow prevention valve on the water line feeding the water heater can save significant energy, and keep the cold tap water from becoming undesirably warm.”
Pfeiffer advised his audience that he is more used to working in the South and that other strategies, materials and methods may be more appropriate for other localities.
A good ongoing source of information on green building, he said, is Environmental Building News.
For more information on NAHB’s green building resources, e-mail Calli Schmidt, or call her at 800-368-5242 x8132.
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