Recently, I toured a 125-year-old home on the South Side of Chicago that will cost its owners about one-tenth as much to heat and cool as a typical Chicago home of its size. The difference is in the building envelope. An inexpensive, double-radiant barrier cuts heating and cooling loads by 40%. Low-E windows keep heat out in summer but let it in during winter. Soy spray-foam insulation achieves R-28 in the walls, and wet-spray and dense-pack cellulose are used for plumbing walls. The home exceeds Energy Star requirements by 80%.