Well my personal case is a mid-size apartment (130m², ~1399ft²) in a building built in the end of the sixties to a newly build home around 210m²/2260ft². Old a

Well my personal case is a mid-size apartment (130m², ~1399ft²) in a building built in the end of the sixties to a newly build home around 210m²/2260ft². Old apartment was heated by a central methane based burner, new house by a VMC with a heat pump and a two solar thermal vacuum panel + 800l heat cumulus (~28ft³/ 211 US gal / 176 UK gal), whole cost dropped around 80%, whole energy consumption drop from around 300-350w×m²/years to around 25w×m²/years... But in medium in the whole country individual homes are newer than tall buildings mostly because they tend to be poor quality to a point that's cheap demolish and rebuild than maintain and also tall buildings are normally property of many different subjects so reach agreements on any upgrade / maintenance is far complex than individual houses and physical space and usable ground for construction around the home is normally far more present than around a tall building... Keep attention that I always talk about mean values, not single buildings. Another thing, I do not know in the USA but in Italy and France construction norms are less tight for airtightness in collective buildings than individual houses, airtightness often play a more prominent role than insulation thickness in term of energy cost. I do not know in big buildings how for instance a VMC (mechanically controlled ventilation with heat exchanger) can possibly work...