A few years ago, when my youngest daughter was 5, her aunt asked he could she spell  " supercalifragilisticexpialidocious", my daughter looked at her very seriously and asked "can you spell cat"

I learned, that no matter how complicated the task, it starts with the basics.  

There are four basic ingredients that you need for comfort with energy efficiency.

1. Generate the heating, cooling and  ventilation efficiently

2. Distribute the heating, cooling and  ventilation efficiently

I've often come across customers building a "low energy" or "near passive" house.  The thing is, in all these descriptions of what they would ideally like - no or a very low heating bill, the most important item missed in achieving their goal is air tightness.

Far too often, insulation companies push the merits of insulation, our building regulations push U values.  Both are meaningless without air tightness.