it's the manufacturing, stupid

I hate that so much "green building" research, investment, and of course marketing is focused on new houses. (Example here, with free plans even.) While it may make people feel better about the brand-new houses they're building (usually on formerly undeveloped land), in most cases the manufacture and transport of the materials are far larger energy-wasters than living in an older, less-than-ideally constructed home. It's better than building a standard McMansion, yes, but not better than getting by with a house that's already there.

Some exceptions may exist- in some cases, it might be environmentally benign to build with materials gathered or harvested from or near your own land- stone, strawbale, cordwood. But improving existing housing stock almost always has a better payoff.