My house is 101 years old. It is not a “lovely old vintage home”, it was a tract house in 1920. So, to answer your question, All Of Them. The wiring is funky, the plumbing is funky, insulation has been quite a workaround, and every time the wind really blows (I live in hurricane land) things shift oddly. Bit by bit I keep disaster at bay, but it’s a lot like adopting a pissy adult dog. But, hey, it’s my cranky old dog, and we have learned to work together. :-)