Protecting Bonus Room Above Unheated Garage from Moisture, etc.

We have a detached garage fully wired but no heat. The first floor is a standard concrete/cement garage floor, unfinished but some R-19 insulation between the studs of the open walls. There is a metal gargage door with opener. The garage is a high ceiling. There are stairs up to the bonus room - about 8 steps to a landing and then the stairs go up to the left (at a 90 degree angle). There is no door between the first floor and the upper bonus room. There is sheetrock on the bonus room roof. There is visible space at the top of the ceiling on the first floor so you can see just a bit into the upper floor. Long story, sorry, but my questions are just what should I do to keep the humidity and moisture to an acceptable level in the bonus room? Should I use a dehumidifier? Should I add some wall heaters? Am I overly concerned about the effects on the room, ceiling, and items we may store in the bonus room that our wet northwest may bring? Shouild I add some sort of door between the downstairs (garage) and the upstairs (bonus room)? Thanks so much for listening and for any suggestions. J-man

 

If you want to condition the upstairs and not the garage level, they will have to be separated. Check your local codes regarding isolating the garage space from living space, even though you may not be parking a can down there or sleeping up top, codes on living space over a garage are strict and for good reasons.

Cover that fiberglass with sheetrock or other air barrier to avoid condensation on the cold outside walls. And do check on air sealing and fire barrier requirements.

Bud