I live in a flat that was built mid 90's and it's a disaster from a heating and cooling point of view.

Ventiliation is shit, one side never gets the sun so the outer wall is cold which means condensation is a daily battle, I basically run a big heavy duty dehumidifier from mid-autumn to mid-spring (at least its not a net loss, it dumbs a fair amount of heat as a byproduct so I can run the heaters less).

It's rented though so not something I can fix until I buy a property in a few years.