I've been an energy consultant to Colorado builders for the past 20 years, and since 1993 I've done detailed performance tests on nearly 200 homes in the state. Based on that experience, here are the energy-saving features I most strongly recommend to both production and custom builders in my home state. All five measures are proven and widely accepted, which should make them equally useful to builders in other cold-climate areas. Tighten the Ductwork Leaky ductwork is common everywhere, and it's a bigger problem than many builders realize. It reduces comfort and wastes energy, but it is also a potential safety problem. During one recent six-year period, there were 352