The urban heat island effect strains the ability of city dwellers to keep cool during the summer months. As this thermal threat is expected to intensify in a warmer future, options are needed to thwart the ingress of ambient heat in city structures and to tamp down cooling energy-related costs and consumption. Researchers from U.S. Argonne National Laboratory and U.S. Pacific Northwest National Laboratory are looking up for a solution by evaluating roofing materials that cool surrounding outside air and reduce the need for air conditioning (AC).

A regional climate model simulating the Chicago, Illinois, urban region during a heat wave event assessed the cooling comfort contributions of roofs painted a heat-reflecting white, covered with vegetation or sporting solar panels. All three design options were observed to reduce the near-surface temperature and AC consumption demand during daytime hours when air temperature peaks.

White-painted roofs reduced the near-surface temperature by 1.5° C, followed by 1.2° C for vegetated roofs and 0.6° C for solar panel roofs across the Chicago area. As all the roofing strategies offer cooling effects, they reduce AC consumption, with painted roofs delivering the greatest reduction, followed by vegetated roofs and solar panel roofs. Energy demand was shown to be reduced by 16.6%, 14.0% and 7.6%, when these options are deployed, respectively.

The research published in Science of the Total Environment underscores the cost-effectiveness of large-scale installation of white-painted roofs in terms of cooling effects and cooling energy saving. These cost less than the other two technologies and do not require additional water, but do not provide the stormwater management benefits of vegetated surfaces. Stakeholders are urged to use these results to inform sustainable development approaches, lower summertime cooling energy demand and help minimize greenhouse gas emissions in urban environments.