All had R-19 insulation installed on the attic floor except in the configuration with the double roof (Cell #2) which had R-19 of open cell foam sprayed onto the bottom of the roof decking. The measured thermal impacts include ceiling heat flux, unintended attic air leakage and duct heat gain. We also developed a new analysis method to estimate total cooling energy use impacts of different roofing systems considering the various influences.

The sealed attic double roof system (Cell #2) provided the coolest attic space of all systems tested (average maximum mid-attic temperature was 81.1°F), and therefore also the lowest estimated impact due to return air leakage and duct conduction heat gains. However, it also had the highest ceiling heat flux of all strategies tested, reducing its improvement over the standard black shingle roof. It had the most modest reduction in space cooling at only 7% relative to the standard roof.

A major thrust of the testing for 2002 was comparative testing of metal roofing. Given the popularity of unfinished metal roofs, we tested both galvanized and Galvalume® roofs. Galvalume® roofs are reported to better maintain their higher solar reflectance than galvanized types. Average daily mid-attic maximum temperatures for the Galvalume® and galvanized metal roof systems were roughly similar (19.6oF and 17.3oF cooler than the control dark shingle respectively). Estimated total heat gains were also relatively close for both.

The highly reflective ivory metal shingle roof (Cell #3) provided the coolest peak attic temperature of all cells without roof deck insulation. Its average maximum daily mid-attic temperature was 93.3oF (23.4°F lower than the control dark shingle cell). While the ivory metal shingle roof’s reflectance was slightly lower than the two metal roofs and white metal roof we observed evidence that the air space under the metal shingles provides additional effective thermal insulation.

We also estimated the combined impact of ceiling heat flux, duct heat gain and unintended attic air leakage from the various roof constructions. All of the alternative constructions produced lower estimated cooling energy loads than the standard vented attic with dark shingles (Figure E-2). The Galvalume® roof clearly provided greater reductions to cooling energy use than the galvanized roof even in the first summer of exposure.

An emerging fact from recent testing is that nighttime attic temperature and reverse ceiling heat flux have a significant impact on the total daily heat gain, particularly for the metal roofs. The rank order below shows the percentage reduction of roof/attic related heat gain and approximate overall building cooling energy savings:

The relative reductions are consistent with the whole-house testing recently completed for FPL in Ft. Myers (Parker et al., 2001). This testing showed white metal roofing having the largest reductions, followed by darker constructions.