This information illustrates that there are many misconceptions when it comes to the benefits of black roofs vs. white roofs.
Q: I live in a northern tier climate, and have heard that any summertime energy savings I realize with a white roof will be offset by winter heat loss. Doesn’t a black roof help me save money on heating costs?
A: In the northern tier of the United States, one might think that a black roof would provide a winter heating benefit to building owners. However, there are several factors that make any potential heat gain relatively immaterial:
The laws of physics dictate that hot air will always rise. Thus, any heat that is transferred to the interior of a building structure from the outside will remain at the top of the structure, providing minimal heat savings.
In all parts of North America, there are fewer hours of sunlight to affect energy costs. In fact, in some areas, there is a greater than a six-hour difference between peak-summer and peak-winter sunlight, meaning there is less sunlight available to contribute to a building’s potential warming. Plus, the angle of the sun is less direct, which also helps to minimize warming potential.
In many areas, roofs are covered with snow for much of the winter, turning them “white” and eliminating any potential black roof heat gain.
The energy required to air condition a building in the summer is usually considerably greater than the energy to heat it in the winter, making the potential for summer energy cost savings much greater with a highly reflective white roof than winter savings with a heat absorbing black roof.
Q: Why is white roofing drawing so much attention from industry groups and government organizations?
A: It’s becoming increasingly clear that along with dark pavement and disappearing vegetation, dark/black roofing is a major contributor to the “urban heat island” effect, which is the tendency of urban areas to reach temperatures three to eight degrees higher than outlying rural areas.
In addition to discomfort and even danger for people who live and work in overheated buildings, the owners of hot buildings also face escalating energy costs, potential energy shortages and accelerated aging of building structures.
In response to this problem, a number of programs have been initiated throughout the country. Notably, the Federal government has mandated a 30% reduction in energy use for Federal office buildings by 2005 and 35% by 2010. Installing a white reflective roof membrane can help reduce those energy uses and costs.
In addition, many cities and virtually all 50 states have mandated cool roofing at some level, and/or offer tax rebates or other incentives to promote the use of cool roofing to building owners.
In such an environment, it’s apparent that, as opposed to dark/black roofs, white roofing systems are part of the solution, not the problem, when it comes to delivering energy