Comparative Evaluation of the Impact of Roofing Systems on Residential Cooling Energy Demand in Florida

Roof and attic thermal performance exert a powerful influence on cooling energy use in Florida homes. The Florida Power and Light Company and the Florida Solar Energy Center instrumented six side-by-side Habitat homes in Ft. Myers, Florida with identical floor plans and orientation, R-19 ceiling insulation, but with different roofing systems designed to reduce attic heat gain. A seventh house had an unvented attic with insulation on the underside of the roof deck rather than the ceiling: (RGS) Standard dark shingles (control home) (RWB) White “Barrel” S-tile roof (RWS) Light colored shingles (RWF) White flat tile roof (RTB) Terra cotta S-tile roof (RWM) White metal roof (RSL) Standard dark shingles with sealed attic and R-19 roof deck insulation Building thermal conditions and air conditioning power usage were obtained. The attic temperature during the peak summer hour is 40F greater than ambient air temperature in the control home while no greater than ambient with highly reflective roofing systems. Light colored shingles and terra cotta roofs show temperatures in between those extremes. Measurements showed that the three white reflective roofs would reduce cooling energy consumption by 18-26% and peak demand by 28-35%. The terra cotta tile roofs and white shingles would produce cooling savings of 3-9% and 3-5%, respectively, while the sealed attic construction with an insulated roof deck would produce reductions of 6-11%.

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