Warning, annecdata: we turned down our heating signifcantly this winter, and both my roommate and me have gotten quite a bit of mold on and around our windows.
The thermostat is now back up to 19.5°C.
The thermostat is now back up to 19.5°C.
But drywall (and other porous surfaces) are supposed to help regulate moisture, so if they never get an opportunity to dry because it's permanently cold and humid, yeah, that'll be a problem. Cracking a window at least 30 minutes per day (ideally on dry days) does wonders, though it won't help temperatures in winter.
In practice... say, there is a dog that likes to gnaw on corners and thus punctures the vapor barrier. Happened to my own house's outside insulation. That's just one of many "unforeseen" ways how these foils and barriers stop working. I fully expect the polystyrene there to get moldy in 20 years or even less.