"I was surprised while traveling in Sweden two years ago to learn that triple-glazed windows have been, essentially, required by code in that country since 1976." Alex Wilson writes in a Green Building Advisor article. He also mentions Serious Windows which I have been hearing a lot about lately and am anxious to try. Pricing seems very good and I have heard tell that the quality is excellent. I believe that parts of the U.S. will move towards such code legislation in the near future as the severity of the global climate crisis becomes more obvious to Americans.