I have a house from 1965 that I am improving, step by step. It is located in Sigtuna municipality. Now it's time to insulate the cold passage. I have read lots of tips and advice on insulation, but in my inexperience, I can't see that any of them really fit my house.
Against the house is a large cold garage, as long as the house, with a roof that slopes backward at a low angle. I don't know in what order or when things were changed, but a previous owner decided to build a cold passage/service entrance. The cold passage extends inside the garage, along the whole house, and has an exterior door at each end. The roof in the passage follows the garage's roof, but there is a gap of 40 cm between the cold passage's roof and the garage's roof. So, the cold passage's roof slopes. In the cold passage, there are three doors into the house. One door leads to the laundry room, which then has a door into the rest of the house, another door leads to the boiler room (which is inside the house itself but only has a door to the cold passage), and a door to a small "closet". There is also a closet built from the cold passage into the garage, like a little bump, but I will remove that.
The garage is not entirely sealed but does not let the wind through and has an insulated garage door. The garage floor is still just gravel; I can't fix it until next summer, so there is moisture from the ground.
My thoughts are to lay insulation boards freely on the ceiling, install a vapor barrier of plastic sheeting inside the garage against the wall, fasten it with studs, place insulation between the studs, and then OSB boards facing the garage.
My questions to those more knowledgeable than me are:
How thick does the insulation need to be? I am planning to keep the passage at 12-15 degrees.
What kind of insulation is suitable?
Do I need a vapor barrier/moisture barrier?
Is there anything I have missed that I should consider?
