Acute temperatures in uninsulated, ventilated attics affect comfort and energy efficiency in living spaces beneath. Many homeowners elect to seal and insulate the attic, cutting indoor heat gain in summer and heat loss during winter. A comprehensive attic sealing project typically includes applying polyurethane spray foam insulation to the underside of the roof sheathing.
The Insulation Issue
All roofing materials, such as shingles, absorb solar heat. In an uninsulated attic, the heat passes through roof sheathing and disperses into the attic space. Since spray foam insulation applied to the underside of roof sheathing inhibits heat conduction and dispersion, homeowners may wonder if overheated roof sheathing will degrade performance and service life of the shingles above.
Minor Temperature Increases
Research conducted by the Florida Solar Energy Center demonstrates that insulating the underside of roof sheathing causes only negligible temperature increase in shingles. Compared to an uninsulated roof, the normal temperature in shingles over insulated sheathing ranged from 2 levels to nine degrees Fahrenheit warmer, nicely within specifications mentioned by shingle makers. Researchers found that variables such as shingle color and orientation of the roof into solar exposure had far greater influence on shingle temperature than insulating material applied to roof sheathing.