The joint influence of albedo and insulation on roof performance: A modeling study

• Validated a roof model to account for building-environment energy exchanges.
• Optimum combination of roof insulation and roof reflectivity calculated.
• Albedo of 0.6 and insulation thickness of 46 cm ideal for New York Metro.
• 13 years to recover the additional cost incurred for doubling insulation thickness.

The advanced Princeton Roof Model (PROM) is evaluated and then applied to quantify the heat transferred through various modular roof structures over an entire year. The goal is to identify an optimal combination of roof reflectivity and insulation thickness that will reduce energy consumption and minimize cost. Meteorological data gathered over the Northeastern United States (Princeton, NJ) is used to force PROM. Our results reveal that for new constructions or for retrofits in the region, an R8.4 (around 46 cm thick roof insulation) white roof (assumed albedo = 0.6 or greater) would significantly reduce the combined heating and cooling load attributable to the roofs. The wintertime penalty of white roofs is also shown to be insignificant compared to their summertime benefits. The findings are pertinent to many other densely populated areas with comparable climates where, despite a much higher number of heating versus cooling degree-days, white roofs are overall advantageous. A cost optimization analysis found that doubling, tripling and quadrupling the insulation thickness from the baseline case of 5.08 cm (2 in.), at an albedo of 0.45, requires 13, 17 and 19 years, respectively, to recover the additional cost incurred.