Earlier quoted context omitted.
> Maybe go a step further and wear long underwear and maybe even a hat; why not? Some reasons why not: you may live with other people who have different basal temperatures from yours, aren't comfortable at 16 degrees or whatever you settle on, and didn't consent to participating in your wacky experiment; other people may come over to visit your house without realizing in advance that they need to wear long underwear;…
> other people may come over to visit your house without realizing in advance that they need to wear long underwear; Not a problem in Covid times. But it's possible to turn the heat up when you have guests, no? Or run a space heater in the living room when they're around? > and low indoor temperatures promote mold growth. I'm mystified by this. I thought moisture promoted mold growth. The solution to that is good ven…
There is a related problem when insulating your house more. If it's badly insulated, walls are cold and any dampness happens on the inside surface of the wall. You turn up your heater and ventilation and it evaporates.
Now you add more insulation. Your walls on the inside are warmer. But the absolute humidity in the air is still the same, so it goes into the wall too. There is a temperature gradient inside the wall. When it's cold outside, there is a point in the wall where the relative humidity hits saturation, so the wall gets moist there. The better insulation, the deeper this is in the wall. No level of ventilation will save you here and if you don't do anything about it, you get mold inside the wall. Which you would not get without this extra insulation.
The solution is vapour barriers. They need to be close to the inside of your walls to work. This is a tricky subject and part of the reason why adding insulation after the fact is hard.