Quote:
Originally Posted by spinner1001
The theory for adding attic insulation above the garage is to slow the heat transfer from the hot attic into the garage. With insulation, that certainly occurs in some degree. But the practical decision is whether that benefit is worth the cost of the insulation. The trade off is subjective.
I recently added insulation to the garage door and attic above the garage and can feel a noticeable difference in the garage temperature. I believe both have an effect on the garage temperature but I don’t know whether the door insulation or attic insulation has a bigger effect. My garage door faces the sun in the afternoon.
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Note that hot air rises, so I'm not sure how much benefit the ceiling insulation provides. I think that adding a ventilation fan to remove the hot air from the attic would provide more benefit.
Follow-up. To test your theory, I measured the temperature inside my garage about one inch from the ceiling. It was 92 degrees, which was the exact same temperature as the outside air. Also, there was only about a 2 degree temperature difference 5 feet below the ceiling (90 degrees). I think that is attributable to the hotter air in the garage moving up toward the ceiling. The attic temperature was about 10 degrees hotter than the outside air. There is zero insulation above the garage ceiling. So, I don't think there is much heat being transferred downward into my garage from the attic.