Suppose we built homes with high ceilings to handle summer heat. I don't know what it is like where you are, but around here in addition to summer we also get something called winter, and it isn't nice to warm a wad of air and have it waft away above your head. So suppose your rooms had a removable lower ceiling. (Yes, with some ventilation, with one panel carrying the power, etc, etc) In winter you heat the smaller volume and in summer you take advantage of the high ceiling.
Lay out streets so you can build homes that take advantage of prevailing winds. Ours doesn't--the winds tend to blow against the garage rather than the front or back.
Homes aren't designed to be easy to expand (granted there are insulation and roofing issues that make expansion complicated). Not all of us have 2.3 children; how do you take in an ailing parent?