An interesting article on the cost benefit of PassivHaus, that seems to conclude that PassivHaus is a fantastic standard to look at, to work towards, but that going the whole way on all points, and getting PassivHaus certified does not currently make economic sense (and possibly environmental ?) given the benefit of those last steps.

This sounds very much like the 80:20 rule where it takes most of the effort to get the last 20% of the gain.

http://www.homebuilding.co.uk/feature/passivhaus-analysis

….. better thermal performance and it will cost less to run, but it is likely to be in the region of £5 to £10 per month. Whether that is enough to justify the extra investment is the issue.