The first stage energy efficient home design is just that; a home design that is better for energy efficiency in comparison to a home that is built without considering efficiency. These homes are cost effective but have plenty of room for improvement.
The 2nd stage energy efficient home design is a step up from the first stage in terms of energy efficiency. The initial costs are higher when building this kind of home but the energy savings over time more then compensate for what you pay initially.
The 3rd stage energy efficient home design is the ultimate home design for maximum energy efficiency. These homes cost the most to build, but the end result still saves you thousands of dollars in energy bills, even on the shortest mortgage time frame.