I'm a building energy consultant in central Wisconsin. I recently had a chance to perform a major energy retrofit on a modest ranch-style house just south of Lacrosse, Wis. It was a simple two-bedroom home that was probably built shortly after World War II. Such homes are quite common around here; I've heard them called "farmer's widow" houses because they're too small for a typical family. The original house covered just 700 square feet, and a 1970s-era addition off the back provided an additional 500 square feet. The basement, used mostly for storage, added another 950 square feet of conditioned space.

Like many houses of its time, this one was leaky and very lightly insulated, making it expensive to heat and uncomfortably drafty. But it was located in a pleasant established neighborhood where no new building lots were available. While tearing down the existing structure and building a new one on the same site would have been a reasonable...

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