Wary of Waning Power Supplies, Eco-Minded Architects Build a Better Box

Katrin Klingenberg's passive house in Urbana, Ill., can be heated with 10 100-watt light bulbs. It's 90 percent more energy efficient than conventional houses in the area. (By Katrin Klingenberg)

In a renovation, these modifications can often be retrofitted. Either way, the house will be so airtight that mechanical ventilation must be added. However, heating equipment can be much smaller.

Even more insulation can reduce heating requirements to the point that the heat given off by the building's occupants, appliances and lighting, plus the passive solar heat streaming in through south-facing windows, is sufficient for the entire house. This approach, called the passive house, was pioneered in Germany in 1990. About 9,000 such buildings have been built in Europe.

The first passive house in the United States was built in Urbana, Ill., in 2003 by Katrin Klingenberg, an architect and a professor at the University of Illinois. She said she can heat her 1,200-square-foot house with 10 100-watt light bulbs.

To accomplish this in Urbana, where the temperature can fall below zero during the winter and rise above 100 during the summer, her walls are 16 inches thick, the insulation in her attic is 16 inches thick, the windows have three panes, and the underside of her concrete floor slab is insulated to a depth of 14 inches. (There is no basement.) Her house is 90 percent more energy-efficient than a conventionally built house in Urbana.

In Florida, which has a relatively benign climate, a passive house would be far easier to build, said Danny Parker, a senior research building scientist at the Florida Solar Energy Center in Cocoa.

In Florida, unlike in the Midwest and the Northeast, you save energy with a building that keeps the heat outside. The change in wall thickness from adding insulation would be barely noticeable -- it's about 1 1/2 inch. White roof tiles and white siding would reflect heat from the house.

Other modifications include dual-paned windows with an energy-efficient coating, a three-foot overhang to shade the walls below, added tightness to prevent hot, humid air from leaking in, and carefully sealed air-conditioning ducts that are within the cooled space. These steps would reduce energy needs by 72 percent compared with a conventional house. Tile floors would reduce cooling needs even further.

This strategy is so effective that a house that incorporates them would be cooler without air conditioning than a conventionally built house with the air conditioning running, Parker said.

Once you've reduced the energy loads, what about the backup system?

The most cost-effective choice is a gas or propane generator, even though it uses fossil fuels, all three building experts said. Foley, the Maine architect, sizes one to provide enough power for "comfortable camping" -- heat, well pump, ventilation, refrigerator and a few lights.

To get this level of power using alternative energy -- a sun-powered photovoltaic system and batteries that provide power at night -- is prohibitively costly unless the house is quite small, he said.

In Florida, a photovoltaic system and batteries would be more feasible because "comfortable camping" there requires less energy than it does in Maine, Parker said.

For more information on the Passive House, see http://www.e-colab.org and http://www.passivehouse.us.

Katherine Salant can be contacted via her Web site, http://www.katherinesalant.com.

© 2008 Katherine Salant