Austin Architect Provides Tips on Green Building - 4/12/2004 - House Energy Efficiency

Austin Architect Provides Tips on Green Building

Reminding his audience that his green building practices are most appropriate for building in the South, Pfeiffer said that home builders, by employing a little thought and creativity, can come up with mainstream solutions that use locally appropriate strategies, materials and methods.

“An igloo would not be a green building in Arizona,” he said.

Pfeiffer emphasized the importance of minimizing solar gain in the summer and maximizing it in the winter, and in his area good orientation also includes taking advantage of prevailing breezes, he said.

Properly orienting "buildings in Austin to the Southeast would cut energy consumption in half,” Pfeiffer said. “The return on investment in a tankless hot water heater is a drop in the bucket by comparison.”

Following that strategy, he was able to design a 6,000-square-foot house that consumes no more energy than a two-bedroom apartment.

Big overhangs on windows and doors are key, he said, and he recommended using the readily available Sun Angle Calculator to size them.

“High-performance glass lets in 40% of the sun,” Pfeiffer said, “but a shaded window lets in no sun. Shading on windows is more effective than $20,000 worth of glass. Low-E glass is no substitute for good passive solar design.”

“Permanent awnings add five times to the life of doors,” he added.

Pfeiffer also emphasized the importance of limiting infiltration of outside air into the home and maintaining indoor humidity below 50% — which is especially a concern in Austin’s humid climate.

Among specific tips he provided:

• Avoid using vapor barriers on the inside surface of exterior walls — including vinyl wall coverings — in buildings where air conditioning is used for a significant part of the year. These can trap moisture in walls and lead to serious mold problems.
• Go easy on recessed — even “airtight” — cans, which can puncture the thermal envelope of the building. The same applies for light switches and electrical boxes on exterior walls.
• Never use anything but well-sealed ducts to move conditioned air. Unlined return air wall chases are especially bad, as are open return air plenums above dropped ceilings and using floor joist cavities. “We see this mistake being made a lot,” he said.
• Closed or open cell spray polyurethane foam insulation — such as Demilec or Icynene — is especially effective in reducing infiltration. Wet blown borate-based wall cavity insulation and cellulose are also effective.
• Venting crawl spaces and the attic can create moisture problems. Sealing the attic and passively ventilating a continuous air space immediately below the roof decking, not the attic, is better.
• Learn how to flash windows and doors correctly.
• Avoid dark roofs, which absorb heat. A radiant barrier on the underside of the roof will substantially reduce heat gain through the roof; they need to be installed in conjunction with an air space and will not be beneficial if they are in direct contact with another building material.
• New types of fluorescent lamps — especially the thin T2, T5 and T8s — provide superior light quality. Proper day lighting, especially indirect daylight from high windows, can yield substantial energy savings. Half-screens can be used for day lighting; they are a good solar screening device.
• Proper sizing of the air conditioning system is critical. “Over capacity can cause mold growth within the ducts and other places within the building or house — leading to poor indoor air quality and occupant health problems,” Pfeiffer said. “With proper windows and shading, most houses should require no more than one ton of cooling capacity for every 600 square feet of living area,” and 700 square feet is very attainable.
• Leaky ducts can depressurize the house, and ducts with a slick interior surface — such as metal — are best for delivering clean air and staying clean. Ducts lined with interior insulation, such as fiberglass duct board, can do the opposite.
• For termite control, consider sand barriers or stainless steel screen barriers such as Termimesh in and around the foundation. Consider spraying the frame of the structure with Tim-bor, a natural brine solution that makes it insect resistant.
• Structural insulated panels from the factory can be assembled in three days and help protect the home from the weather quickly. “A typical home absorbs hundreds of gallons of water before the roof is put in.”
• Use drought-tolerant xeriscaping. “Landscaping uses five times as much water as the inside of a house that has efficient appliances.
• Front-loading washers save water and energy. The washer produces more humidity than anything else in the house.
• Detached garages will increase indoor air quality, he said, because when they’re attached, “you’re sleeping with whatever’s in the garage.” Garages are the biggest source of volatile organic compounds (VOCs) in the home. If the garage cannot be detached entirely, it can at least be connected to the house by a breezeway.
• Natural wool carpet that has been aired out for 48 hours outside of the house reduces VOCs.

go to top