@piraat

Yep. I just did a major refit of my house ( new windows/doors, insulation upgrades, ventilation, solar PV ) brought the house from E2 to B1. All investments worth the effort purely from an ROI/ energy saving perspective.
I had to drop the heat pump from the deal as it literally added no extra benefit in terms of reducing my net energy requirement, but would have cost me €15k extra to install (minimum).