I have a small section of roof over the front of my garage, which I would like to insulate and drywall (making my garage fully insulated).
It is 39" high, and 54" by 17', framed with 2x4 trusses, and facing almost directly north (I don't think it ever gets direct sun). I'm located in south eastern Ontario (near Toronto), and the temperature typically ranges from about -30 to +30C. The garage is not directly heated, though is attached to the house by two walls and so some heat loss from the house is going to heat it (even without being 100% insulated, today when it's 13C outside, it's noticeably warmer in the garage).
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There are soffit vents in this section, and since it is open to the garage below it currently gets some amount of air circulation. I was planning on insulating with R14 fiberglass batts.
Can I close it up without issue, or do I need to add vents of some sort? Presumably I need to make sure there is airflow from the soffit vents at least. Since this is the front of the house, if I do need vents, are there any options for discrete vents?
UPDATE: Spray foam installed
I decided to go with the 'hot roof' method, spraying the underside of the roof decking.
At the advice of the spray foam installer, I put some rigid foam boards blocking the soffit space. There is a continuous thermal break from the walls (batt insulation) to the ceiling (spray insulation).
After the spray foam was installed, I immediately noticed how nearly air-tight it feels, which made me a bit concerned about moisture. Since it's easy to do now (prior to drywall) I'm in the process of adding an exhaust vent that vents outside.
It has gotten as low as 0C out, and the garage was still at a comfortable 14C.