Insulate the garage concrete ceiling or not?

Hello!

Our double garage is currently being built.

I would like to read your opinions on whether insulation of the concrete ceiling makes sense, as opinions seem to differ.

Here is what I can write about our project so that maybe something appropriate can be said;

The 6x6.7m large double garage with a partition wall is not connected to the house and is freestanding in the front garden area.

Floor construction; approx. 65cm gravel, strip foundation, approx. 15cm deep waterproof concrete measured in the middle, without insulation, approx. 6cm screed
Masonry; 17.5 limestone sand brick, lime cement plaster with insulation components
Iso 45 doors from Novoferm
Flat shed roof with 6% slope

Cars will be parked there and some stuff for the garden etc.
No DIY work or hobby activities planned. No heating intended.

Is insulation really necessary on the concrete ceiling under these conditions?

Insulation doesn't make sense in my opinion, the garage is cold anyway. You are just causing condensation.

Especially in the winter months, you will have a problem with mold formation on the garage ceiling:

A lot of moisture is brought into the garage with the cars, which evaporates there.

The indoor air of the garage is, since unheated, cold but warmer than the outside air, especially at night. Where are the coldest spots in the garage then? The walls and especially the ceiling. If the wall adjoining the house is not the north wall of the garage, then that one is particularly cold.
Consequently, the room air will condense on this cold ceiling (thermal bridge) and mold formation will occur.

Now one can argue about how much insulating the ceiling helps.

In your place, I would immediately turn all the screws available:
Insulate the ceiling and, if possible, also the outside walls of the garage (you had already mentioned insulation components).

The garage door is relatively airtight, which is basically good. However, you have to lead the humid air outside. I recommend considering core drillings for supply and exhaust air in connection with fans and a dew point-controlled ventilation system (search once for that on the internet).

I would paint the ceiling and the interior walls with an antifungal paint, e.g. paint containing silver.

Finally, I would plan the possibility of having at least one heating pipe laid in the garage. If everything described above is not sufficient, a small radiator can be retrofitted later. Although this is energetically suboptimal, the garage should at least be somewhat insulated, and it is not supposed to be heated to 20 degrees there. So if the radiator runs for three weeks a year, I would prefer that over mold formation. Even if you want to set up a workshop corner in the garage, you will be grateful if the temperature there is not 2 degrees but 12 degrees…

An airtight garage is bad in many ways. The moisture stays on the car and it rusts much faster. Not good for the electronics either. Since you don't plan to heat the garage, make sure there is air exchange in the garage. That also makes the question of insulation unnecessary.

I also think that it makes little sense if an unheated garage is only insulated at the ceiling.

We will probably skip the insulation, simply apply a bituminous membrane on the roof after concreting, and that's it.

I will think about the air circulation.

Please also provide a Wi-Fi router for the smart home control of the radiator. It should be a panel radiator; this is simply better for some car models!