[michpoch]

I see some early trends in Poland (a lot of soviet-style concrete blocks of flats) where the modernisation is done better.

Article in Polish, but worth translating or just looking at the photos: https://www.money.pl/gospodarka/w-tym-miescie-nie-martwia-si...

Shortly: insulation, new windows, solar panels, heat pumps (heating + warm water).

They do not show "before" photos, but I found some similar building before renovation on the same street: https://www.google.com/maps/@51.3586963,21.5793371,3a,75y,16...

They mention 90% savings in heating costs, which apparently pays off the debt they had to take to make the upgrades.