So I recently had a new 30x24 detached garage built and intend to leave it mostly unfinished. I live in Iowa and we have pretty cold winters here, which will be coming soon, and I'm looking for a low-cost way to provide enough insulation to allow me to heat my garage when I want to do some work in it during the winter. I have a 5,000 W electric garage heater installed, but it has no chance in keeping up with the winter as the garage is now. The garage was installed with no roof vents, but all of the soffits are vented.
I've already installed fiberglass insulation on all of the walls and my concern is now the ceiling. I may drywall the ceiling at some point in the future, but definitely not this year. My questions is the best low-cost and fast way to provide at least a reasonable amount of insulation in the ceiling area. Can I insulate the soffits to try to reduce the amount of air/draft that comes in through the soffits, at least for the cold months? I figure this would be a cheap and easy solution, but I'm not sure if it would solve the problem or is a good idea. Alternatively, would it provide much of a benefit to install vapor barrier on the ceiling and then leave the soffit vents open (so the roof area would be vented).
Again, I'm not looking for a super insulated garage, I just need something that I can work in and heat on occasion. Right now every time the wind blows half of my heat is lost from the air coming in through the soffit vents.