I'm not sure how the Austrian system works or what homes are like there or in the Netherlands, but a lot of older homes in the UK can apparently only reach a D

I'm not sure how the Austrian system works or what homes are like there or in the Netherlands, but a lot of older homes in the UK can apparently only reach a D even after all the standard insulation retrofits are done. This is especially a problem in areas of the UK that are poorer already.