How old is this building you're describing? There's been some pretty huge changes in the past 20-30 years, older houses are shocking for insulation but modern ones are often pretty good.
The building codes evolved at lot up until roughtly 10 years ago. Houses from before the 90ies is not that well insulated with lots of cold bridges. They have mostly been eliminated from new buildings, but it does make building quite a bit more complex.
