A.Michael Holtz responds: Designing the most cost-effective building envelope requires analyzing the entire house as an energy system and making tradeoffs between insulation levels, glazing type and area, and mechanical equipment efficiency. The various energy components in a house should be balanced to get the maximum savings for the money invested in energy improvements.

To determine how far to go with energy conservation, you need to evaluate how much energy each measure will save and what it will cost. Only then can you decide whether the additional expense is justified. For example, let’s look at a 1,500-square-foot, single-story, wood-frame ranch house built on a slab foundation. The base design has R-11...

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