I have a moto that I live by when building: Fanatic Insulation. I’m not sure if I coined the phrase but I think I did :). We use weather barrier, caulk, insulation, foam, flashing etc like there we’re building an antarctic deep sea submarine.
Considering some European standards, notably in Germany, our insulation style actually isn’t that fanatic. Just recently I was reading about homes in Germany that are so well insulated that in the dead of winter all they need is a little portable heater to heat the entire home. Or one small fireplace. Now that is energy smart!
A house needs to seen as a living entity and a renovation is an operation. When you sew them back up again it needs to be done with thoroughness and accuracy. You wouldn’t leave a patient with a gaping hole in them and the same applies to a house. It needs to be sealed correctly with the correct materials.
Otherwise “infection” will occur. In the form of wood rot from water, wasted energy from air, etc.
Now of course the houses in Germany aren’t just warm because of insulation. They are “passive houses” and of course passive heat from the sun helps.
And if a house is fanatically insulated then you have to give it “artificial lungs” since it is no longer breathing through the cracks in the walls. Fans, windows, air circulators and vents need to be added intelligently so that the house can breathe otherwise the very well insulated air stagnates in it’s own soup.
The key in this is to do it more effectively than the cracks in the wall that while letting the house breathe also let in the elements. A heat transfer plate is one cool tool where the heat going out the house heats the air coming into the house. Likewise you can have the same tool for the water; where the hot water going out of the house (shower, dishwasher etc) heats the water coming into the house through heat transfer coils.