To combat these effects, the city launched the NYC CoolRoofs program in 2010 to convert the asphalt-topped, heat-absorptive black roofs to reflective white. The program has been testing three different types of white roof coverings--rubber, plastic, and paint--to determine which one to implement city-wide. And last week, the first scientific study comparing the three rooftops was published.
"It's an ambitious effort with real potential to lower city temperatures and energy bills," said study author Stuart Gaffin, a climate researcher at Columbia University, in a press release. "City roofs are traditionally black because asphalt and tar are waterproof, tough, ductile and were easiest to apply to complex rooftop geometries. But from a climate and urban heat island standpoint, it makes a lot of sense to install bright, white roofs. That's why we say, 'Bright is the new black.'"
The study, published in the open-access journal Environmental Research Letters, found that the plastic coating kept roofs 42 degrees cooler and lasted for three years -- meeting the Energy Star Cool Roofing performance standards.
The rubber covering did not lower roof temperatures as significantly, while the paint's effectiveness halved after two years.
It's unfortunate that the paint did not hold up over time, which prevented it from meeting Energy Star standards, because it is by far the cheapest method. Even so, Gaffin argues that it may be the best hope for easy, cheap city-wide implementation.
"It's the lowest hanging fruit. It's very cheap to do; it's a retro-fit. You don't need a skilled labor force. And you don't have to wait for a roof to be retired," said Gaffin. "So if you really talk about ways in which you brighten urban albedo, this is the fastest, cheapest way to do it."
Photo: NYC CoolRoofs/Samantha Modell