Cooling from the Top Down: White Roofs

Join the Community Conversation as the Human Impacts Institute investigates Cool Roofs: What color is your roof?

In a previous blog, I wrote about New York City and how it experiences the urban heat island effect. Within the post, I mentioned a few of the steps New York City has been taking in order to reduce the UHI effect, one of which is the NYC°CoolRoofs project, which was a way to reduce the amount of heat city roofs absorb from the sun throughout the day.

According to the NYC°CoolRoof’s initiative, on “a typical summer day, flat, black asphalt rooftops can reach temperatures up to 190°F,” which is almost double the surrounding air temperature! This, in and of itself, portrays the amount of heat a normal roof retains and emits to its surrounding areas, and the need implent a strategy to reduce the amount.

By applying a reflective white coating to roofs, one can reduce the amount of heat absorbed by the roof and subsequently “reduce internal building temperatures by 30%,” which would make the building cooler while also reducing energy costs and carbon emitted by the building from cooling mechanisms such as an air conditioner. PlaNYC says that for every 1,000 square feet of roof that is made ‘cool’, the city can reduce its carbon footpreint by 1 ton of CO2, which would not only improve air quality locally but also help reduce our affect on climate change.

Cool roofs also extend the lifetime of roof. Naturally, all surfaces expand and contract due to fluctutations in temperature; a roof is not exempt from this process. Therefore, when a roofs temeperature fluctuates it also expands and contracts which affects the roof and wears it down. However, when a roof is painted with the cool roof specialized coating, it does not experience the same level of fluctuations as a black roof would!

It is important to note that painting a roof white is not the same as treating it with the coating material. While painting a roof white does increase the reflectivity and reduces the absorptive properties of the roof, the coating material utilized by the NYC°CoolRoofs initiative is distinctive in that it provides a higher reflectivity rate than traditional white paint would and also has high infrared emissivity. Solar reflectivity refers to the roofs ability to reflect visible infrared, and ultraviolet waves while infrared emissivity indicates the roofs ability to emit the rays that it has absorbed. When a surface is able to ‘let-go’ of or emit the heat that it has absorbed at a faster rate, this will allow the surface to be cooler and also allow the building itself to be cooler.

Overall, there is no downside to cooling a roof. You reduce energy costs, ensure a longer lifetime for a buildings cooling equipment (air conditioners), reduce the amount of electrical power used by the building, lower air pollution and greenhouse gas emissions

New York City has already coated 1,586,5744 square feet in roofs and you can easily get involved by convincing your building owner to coat your roof, coat your own roof, or volunteer to help other coat their roofs! By doing so, you will be helping New York City reach its goal in reducing 30% of emissions by the year 2030!

Check out the 2010 annual NYC°CoolRoofs review.

By Muge ‘Mugzy’ Undemir, 2011 Human Impacts Institute Climate and Coalition Building Intern

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