Recently released information from an ongoing study by researchers at the Tennessee Valley Authority (TVA) and Oak Ridge National Laboratory (ORNL) should be of interest to cost- and energy-conscious builders in warm, humid climates. The study found that a relatively modest upgrade in insulation and HVAC equipment can dramatically reduce a house’s annual energy use. Three houses. The TVA-ORNL project is based on three houses built in 2008 in the same suburban Knoxville, Tenn., development. The all-electric homes share the same orientation and are built using identical stock plans for a conventional three-bedroom, 2,400-square-foot home. The first, termed the builder house, is typical for the area: It’s built on a slab, framed with solid lumber spaced 16 inches on-center, and insulated with R-13 fiberglass batts in the walls and R-30 loose-fill fiberglass in the attic. 

The second house, known as the retrofit house, incorporates a modest package of energy upgrades, all of which could be easily retrofitted into an existing home without opening walls or adding insulation below-grade. These include upgraded windows (sash with more efficient glazing were added to the vinyl windows found in the builder house) and an...

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