In 1990 European physicists set out to test the limits of cost-effective energy efficiency. The result was the first passive house, a four-unit townhouse that combined heavy insulation, airtightness, and heat-recovery ventilation to achieve reductions of up to 90% in the energy required for heating and cooling. This program introduces the passive house concept-popular in Europe, but slower to catch on in the States-and showcases some beautiful examples...