The Apartments at 31-81: Installation of Energy Efficient Roofing
Utilizing a true white granule based roofing material, the roof on 31-81 now delivers both long-wearing reliability and energy savings to those living under it. Among other benefits realized after installation, the building is cooler in the summers, cleaner and as a result, consumes less energy. In the United States, dwellings tended to be built with white roofs through the 1960s. Then, as air conditioning became widespread, cheap, and taken for granted, priorities shifted. It became popular to use darker roofing shingles, which more resembled wooden shingles and better concealed dirt and mold. The colored granules on typical "white" shingles made today are coated with only one-sixth as much white pigment as in the 1960s. Under the summer sun, modern roofs can become up to 20°F hotter than the old-style ones.
Why a White Roof?A
Heat Island is is a metropolitan area which is significantly warmer than its surroundings. Heat islands do not primarily arise mainly from heat leaking out of cars, buildings, and factories. Rather, dark horizontal surfaces (such as flat roof surfaces in Queens) absorb most of the sunlight falling on them. Consequently, dark surfaces run hotter than light ones. The choice of dark colors has caused a problem of radiating heat both during the day and well after sunset. Based on the findings of
"heat island" studies performed in
New York, Los Angeles, Chicago, Washington, and Atlanta, a white or nearly white roof has been shown to reflect solar radiation during the day and will not radiate much heat at night.
We are now paying dearly for this extra heat. Some studies have put the estimated energy to cool buildings in the U.S. at one sixth of the total energy consumed by the country (at an estimated annual power cost of $40 billion). Moreover, a 5°F heat island greatly raises the rate at which pollutants-nitrogen oxides and volatile organic compounds emanating from cars and smokestacks -"cook" into ozone, a highly oxidizing and irritating gas that is the main ingredient of smog.
Fortunately, steps can be taken that can go a long way toward dissipating urban heat islands. One solution is to use lighter colors for roofs and pavement. The other is to plant lots of trees (more on this later), which have a two-fold benefit. First, they provide cooling shade. Second, trees, like most plants, soak up groundwater. The water then "
evapotranspires" from the leaves, thus cooling the leaves and, indirectly, the surrounding air. A single properly watered tree can
evapotranspirate 40 gallons of water in a day-offsetting the heat equivalent to that produced by one hundred 100-watt lamps, burning eight hours per day.
Before and After Images
Before
After
Additional Information
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.