Q. What Temperature Will My Attic Be With Spray Foam?
A. Tests conducted at Oak Ridge National Laboratory, funded by the US Department of Energy, showed that a vented attic with fiberglass on the floor was found to have an attic temperature of 108° when the exterior temperature was 110° and interior temperature 70°. Under the same conditions, an unvented attic with spray foam applied to the underside of the roof had an attic temperature of less than 78°. In fact, the Manual J Residential Load Calculations (page 351), used by HVAC installers, recognizes the benefits of a conditioned attic with foam by
basing load calculations on the following extreme conditions: When the outside temperature is -20°F then the unvented attic temperature is 57°F, when outside temperature is 115°F then the attic temperature is 81°F.