Foundation Insulation by Alex Wilson Part I It is estimated that only about 5 percent of all the buildings in America have insulated foundations. Collectively, the heat lost through basement walls, concrete slabs and crawl spaces from our 100 million or so residential buildings represents half a quadrillion Btu — roughly half the current nucleargenerating capacity in the U.S. When the notion of energy-efficient construction first caught on in the early 70s, an interesting "insulation evolution" began. First we addressed ceilings—they were easy. We could simply add another layer of fiberglass batts or blow in the stuff. Then came the walls. Two-by-sixes weren't that much more expensive than two-by-fours, and we could achieve a much higher R-value. Two-by-eights allowed for even more, as