I have a detached garage in Michigan. I don’t currently have a heat source for it, but I would like to improve the air sealing and make my propane heater (indoor rated) more efficient.

The structure is 25’x25′, 14 feet to the inside peak of the roof, and 9′ to the bottom of the truss. It was built in 1995 and has no insulation.

I am not interested in spending thousands of dollars to get the garage to be 70F in January. Realistically, I would like to be able to get it up to 40 when it’s 20F outside, so maybe +20 degrees. I don’t have a big budget for this so it would have to be a low R-value insulation. I don’t anticipate it being heated for more than 10 hours a week in the winter. Ideally the air sealing might let me run a dehumidifier as well.

Is the first step here to seal the soffit baffles to prepare for fiberglass insulation on the roof? Would they need to run the entire length of the interior roof? See attached photos showing open soffits.

Thanks!