Measured energy savings of light-colored roofs: results from three California demonstration sites

Measured data and computer simulations have demonstrated the impact of roof albedo in reducing cooling energy use in buildings. Savings are a function of both climate and the amount of roof insulation. The cooling energy savings for reflective roofs are highest in hot climates. A reflective roof may also lead to higher heating energy use. Reflective coatings are also used in commercial buildings to protect the roofing membrane, and hence, maintain and prolong the useful life of the roof. Reflectivity of coatings changes with weathering and aging which in turn could have an effect on building cooling-energy savings. For that reason, reflective roof coatings are not primarily marketed for their energy savings potential. To monitor the field performance of reflective coatings, the authors initiated a demonstration project where three commercial buildings in California were painted with light-colored roof coatings. The buildings are two medical care centers and one drug store. At all sites, the roof reflectance, both fresh and aged, and cooling energy use were monitored. In addition, they measured temperature throughout the roof systems and inside the conditioned space. In the monitored buildings, increasing the roof reflectance from an initial value of about 20% to 60%, dropped the roof temperature on hot summer afternoons by about 45 F. Summertime standard-weekday average daily air-conditioning savings were 18% (198 kWh) in the first medical office building, 13% (86 kWh) in the second medical office building, and 2% (13 kWh) in the drug store. The overall u-value of the roofs had dictated the impact of roof reflectance.