Questioning the cool roofing movement
As roofing contractors, we can appreciate the fact that building owners and facility managers wish to lower energy costs by reflecting as much sunlight as possible from their buildings. However, "The cool roofing movement," January issue, page 16, smacks of "The Emperor's New Clothes." Should we throw logic and past experience out the window when considering roof systems?
Let's start with heat islands. It is merely logic that tells us where buildings, vehicles and people are abundant, temperatures will be greater than in rural wooded areas. Obvious, also, is the fact that concrete, asphalt pavement and building materials absorb sunlight and increase the temperature in urban settings. Other obvious factors that increase temperature in urban areas are the abundance of vehicles with engine operation temperatures of more than 200 F (93 C); hot emissions from vehicles; and heating, ventilating and air-conditioning exhaust from conditioned facilities. Because roof areas may provide about 10 percent of the surface area in an urban center, should we now target curtain walls of buildings for "cool" coatings? How about asphalt pavement?
I have found no empirical evidence that suggests changing the color of a roof system from gray to white will reduce the temperature of an urban heat island. There also is absolutely no evidence that reducing the heat island effect will increase a roof system's lifespan. In addition, the article's claim that "high reflectivity and emissivity of cool roofs can reduce the heat island phenomenon" is an unproven statement. These factors may provide benefits for a properly designed and installed roof system, but if the roof system is relatively small, on a high-rise building with dark exterior cladding/walls and surrounded by buildings with similar exteriors, the roof system will do little to reduce the heat island effect.