The most cost effective way to reduce the energy used in a home both during construction and while it’s lived in, is to make it smaller.  The average size of a home in the United States has almost doubled since 1970.  I don’t think those of us who were around then felt deprived by the size of our home.

There are some strategies to get more space from the same amount of materials.  One is the row house.  Part of my childhood was spent in intercity Philadelphia.  Our 4 bedroom home was only 20 feet wide though it was quite deep front to back.  Much of the side or what was called a party wall was heated on the other side so there was no heat loss through more than half of the exterior walls.  There was also a surprising amount of privacy with no side windows.  Since the wall and foundation was shared it saved cost, materials, labor and energy.