Quote:
Originally Posted by retiredguy123
I don't know what you mean by "super heat", but, from a scientific heat transfer basis, the ceiling in an unconditioned space will be the same temperature whether it is insulated or not. If the attic heats up very quickly, the insulation may slow down the transfer of heat, but within an hour or so, the temperature above and below the drywall ceiling will reach an equilibrium status and they will become the same temperature. This assumes that you measure the actual temperature of the drywall. So, I don't think the insulation will have much effect, if any, on the tendency for the drywall to crack. The building industry has a long standing policy that you insulate between conditioned and unconditioned spaces, but that you do not insulate between two unconditioned spaces.
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So, eventhough the open lanai is at outside air temperature, the sun beating on your roof will heat up the air in the attic. It can go up to 150 degrees on a very hot day. The insulation will prevent the sheetrock from reaching that temperature. I know this because I put a wireless thermometer in the attic over the lanai and also measured the ceiling temperature before and after the insulation was put in the lanai ceiling. Same goes for the garage ceiling.