Retro-fitting insulation to the walls of an existing building is a tricky subject, with much of the theory yet to be substantiated by real-world experience.
Sash windows in eco-houses: two things that you might not automatically associate with one another. The rationale is discussed in this article.
The topic of ventilation and air flows in dwellings has not, unlike with commercial premises, been given much consideration until recently.
Rainwater harvesting seems like an obvious thing to do to me - capturing the rain that is inevitably going to fall on top of our buildings seems like a even more of a no-brainer than capturing the sunshine that reaches our roofs.