White roofs, Pittsburgh? Think again
Pittsburgh's Office of Energy Efficiency and Sustainability has launched a cool roof program, believing that painting city roofs white will lead to energy savings and other benefits. I work for a Pennsylvania roofing material manufacturing company and have been an architect for more than 30 years with experience in roofing systems design. As the largest producer of both black and white roofing membranes in the United States, my employer has a vested interest in both materials.
The sustainability office's claim that white roofs will result in a 15 percent savings in energy and a reduction in CO2 defies logic and is not supported by numerous energy calculators. Data from the Energy Information Association, and common sense, show that buildings in Northern climates consume at least five times more energy heating the building compared to cooling. What the promoters of white-only options, like Bloomberg Philanthropies, fail to mention or try to downplay is there is a heating penalty associated with white roofs.
White reflective membranes yield their greatest benefit in warm climate regions by reducing air-conditioning costs. Colder climate regions benefit from a darker-colored roof membrane due to increased heating demand in such areas. In either case, insulation plays a significant role in controlling energy consumption, while the roof color becomes only a minute factor. Roof colors' role in energy consumption is reduced as we move up North, where buildings are better insulated, while the number of unintended consequences experienced with white roofs can increase.
There is no inherent superiority to white roof membranes or coatings in cold climates. White's popularity is based on sloppy science and self-serving marketing by companies that offer only white/reflective roofing options.
On a practical level, white roofs in colder climates are also more prone to developing condensation, which leads to lower wind resistance, lower insulation values and the formation of mold within the roof assembly. Similar to how water condenses on the outside of a glass of ice water on a warm day, condensation can build up on the underside of a reflective roof due to the temperature difference between the warm underside and cooler topside. This problem is especially likely for under-insulated white roofs in cooler climates and has been the cause of numerous expensive and premature roof failures.
It is time for engineers, designers, architects and consultants to take a leading role in questioning municipalities, government agencies and building officials regarding the adoption of “green” initiatives and the theories and methods these initiatives use. Those who initiate mandates without understanding the underlying principles should ultimately be held accountable for their misuse.
Samir Ibrahim is director of design services for Carlisle Construction Materials in Carlisle, Pa.