Garage 9x5x3m, adjacent to the house (fire door), flat roof of wooden construction (bitumen on OSB board), rafters 18cm with a distance of about 60cm, outside gypsum board 4cm + plaster, inside a light lime-cement plaster.
The garage has a lifting platform, and plans to heat the garage at low temperatures with an infrared heater. (Above the work area). Does it make sense to provide the garage ceiling with 180mm of insulation, vapor barrier (incl. gluing), counter-battens, OSB boards?
Some say it makes sense because it will heat up a bit, others think the OSB boards will start to rot (I don't understand where the moisture is supposed to come from for this, but maybe someone can enlighten me). My basic idea is that I want to hide the beam structure and install spotlights. I would like to cover the inside of the garages with a nice ceiling (preferably something durable).
What would you recommend?
It's important to have an air level with circulation between the roof cladding and the insulation, otherwise the insulation will get wet in the summer. (Air outside is warm, inside the garage is cool -> condensation on the vapor barrier side of the insulation).
Also, don't use a simple vapor barrier, but a variable moisture vapor barrier. Simply put, this opens up the pores on the warm side (roof) in the summer and lets moisture in on the cold side, inside the garage. There are also flat roof products. In this case, you have to be on your guard.
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).