drop U-values to about half what they are now. Reduce cold bridging a similar amount. Reduce air leakage to a third of current regs. All this has to be proved when the house is built: not a fancy drawing or spec.
How would you actually achieve that ? Houses built today have less than a quarter the U-values houses over 50 years old have. And what would the cost be to the consumer ? What would the savings be ?
I don't believe that air tightness can be reduced to a third of what it is now. What more can you do than polythene all the walls and the ceilings ? If it was physically possible people would probably die of suffocation in their sleep - they would be living in the equivalent of a sealed jam jar.
And btw the air tightness is tested on site after houses have been built, it isn't just proved on a "a fancy drawing or spec".
They are not an efficiency or reduction: they generate power. That is not what is being discussed.
Of course it's efficiency - solar panels are using the solar energy which hits the roof to convert it into either hot water or electricity. If that isn't energy efficiency then I don't know what is, it's "using less energy to provide the same service".
Interesting though that you didn' have solar heating in mind.