[asianthree]

Originally Posted by retiredguy123

The basic concept of insulation is that you add insulation between a conditioned space and an unconditioned space to slow down the rate of heat transfer between the two spaces. Builders do not insulate the garage ceiling because the garage and the attic are both unconditioned spaces. Heat always flows from a hotter space to a cooler space until both spaces become the same temperature. If you park a hot vehicle in the garage, the garage will actually become hotter until the heat from hot vehicle flows into the attic. So, in that case, an insulated ceiling will actually act to prevent the garage from cooling down. But, regardless of whether or not you insulate the garage ceiling, the insulation will only slow down the normal heat transfer process until a state of equal temperature is achieved. This process usually takes less than about an hour. After that, the insulation does nothing. So, insulating the garage ceiling will not result in a consistenty lower temperature in the garage. Actually, in the evening, when the attic cools down, an insulated garage ceiling will slow down the time it takes to cool down the garage.

Interesting thought process. We had Solar guys insulate our south face doors. Asked about insulation above garage. He said give us a call if you add a mini split, without mini split, blown extra insulation in garage is good for snow, not heat. But if we wanted to add insulation to rafters that would help? Thoughts?