Most of the infrastructure in the US was built after WWII, including the entire interstate Highway system and almost all of suburbia.
A substantial amount of housing, especially on East and West Coast, was built prewar or only just postwar. That housing has the potential to have toxic chemicals like lead and asbestos, poor plumbing, lack of insulation, and poor ventilation. It almost certainly doesn't have AC/central heating in places that don't require it year-round to be livable.