Much as I support alternative design/construction and continued experimentation along this line, the simple fact is that a HUGE portion of the North American population lives in wood-frame houses, duplexes, apartments, etc. We're talking construction that goes back 30, 50, 75 years - sometimes more. A lot of it is 2x4 frame... and even when it was insulated with fibreglass (or later had loose-fill insulation blown into empty "dead-air" wall cavities, these buildings are often still not great for holding heat. Sure sealing cracks and obvious air leaks around doors, windows and electrical outlests, and double and triple-pane window retro-fits - but what else?

So this is my question: What are the best Web sites you know of for up-to-date info on upgrading and retro-fitting older homes - not from the standpoint of adding decks or interior design and esthetics ("home makeover") but energy practicality? Thanks goes out to anyone who responds.