Revisions log for Answer #663

Mildew develops when there is a cold bridge in the room and it is not properly ventilated. Therefore, insulation is always recommended from the outside (for walls), from the inside, if you want to insulate the roof in the example, you must make sure that the inner area is completely cut off from the outside, in this case the insulation from the heated area, so that the resulting air moisture can not pass into the insulation and mold develops.

Whether it always makes sense to insulate there depends on what you do in that area, how often and for how long. Do you only park your car there or do you often work indoors? If you're not there that often, hanging the ceiling and installing 2 vents (opposite each other for drafts) in front of which there are manual dampers that can be opened and closed is sufficient. If you plan to spend more time in the rooms, such as parties or working on the car, they are definitely worth insulating (provided the walls, windows and doors are also insulated). For larger events, such as parties, you can also add a heating system that simultaneously heats the pavilion in front of the garage (to account for all possible aspects).