Can the roof of the garage be used as a steam barrier when the weather is MINUS 2 degrees at night?

Yes Buildings with constant temperature and humidity requirements can be provided with moisture-proof layers. Steam barrier This is an airtight and watertight protective material laid on the roof to prevent indoor water vapor from infiltrating into the insulation layer. It is suitable for areas where the indoor air humidity is more than 75% north of 40 north latitude, or other areas where the indoor air humidity is more than 80% all the year round.