"Ninety Percent of U.S. Homes Are Under Insulated"
Yes, because Ninety Percent of U.S. Homes Were Built With Old(er) Building Codes.
> Yes, European homes are also underinsulated, but bricks provide better insulation per default.
A lot of Europe is a lot more temperate than the US and Canada, so it didn't make much of a difference. I'm in Toronto, Canada, and we regularly get -15C winter weather as well as >30C (>80% RH) summer days too. To stay comfortable you really need heating and cooling. Many buildings in the EU don't have cooling (which has caused all sorts of problems during heat waves).
The US has eight climate zones (AK not shown):
* https://www.ecohome.net/guides/3521/climate-zones-map-usa-ca...
And while a lot of the construction techniques would be the same regardless of location (e.g., air tightness), other things would not (insulation, HVAC equipment).