Summer approaches: Think Cool Roofs

“To combat climate change, there’s no question that we need to increase the earth’s albedo,” or reflectivity, Dr. Gaffin said. “Some scientists are contemplating tinkering with the earth’s atmosphere to do this, but we should start with what’s easy and uncontroversial — white roofs.

Before you proceed with this article. One caution is to mind your surroundings.  Cool roofs must be considered in the context of their surroundings. It is relatively easy to specify a cool roof and predict energy savings, but some thinking ahead can prevent other headaches. Ask this question before installing a cool roof:

  1. Where will the reflected sunlight go? A bright roof could reflect into the higher windows of taller neighboring buildings. In sunny conditions, this could cause uncomfortable glare and unwanted heat for you or your neighbors. In these cases, building owners can opt for a cool colored roof to provide some improvement in reflectance without significantly affecting neighboring buildings

Here is a video that captures a case study in NYC. I was particularly interested in the fact that it is a material that is mindful of its historic context, community, and is able to conserve the environment.

Traditional roofs are dark and retain the sun’s rays as heat. During the summer, heat absorption increases roof temperatures, air conditioning costs, energy demand and even local temperatures in a phenomenon called the Urban Heat Island Effect. Cool Roofs can reverse these impacts!  According to the NY Times article White Trumps Black in Urban Cool Contest

Here are some interesting diagrams from that outlines the impacts of when the sun hits a black roof versus a white roof from
Cool Roof Tool Kit.  As you can see you can see there are several environmental implications at hand.

black roof cool roof

Cool Roofs Lower Cooling Costs
A conventional roof can reach very high temperatures on a sunny, windless day. A Cool Roof creates a cooler building envelope, reducing the cost to cool the building in the summer.

Cool Roofs Offset the Urban Heat Island Effect
The Urban Heat Island Effect is a phenomenon in which the high concentration of dark material, such as asphalt and conventional rooftops, increases the temperature of densely built cities by up to five degrees. Cool Roofs mitigate this effect by reducing the number of dark energy absorbing surfaces.

Additional benefits

  • Cool Roofs prolong the life expectancy of the building cooling equipment, which doesn’t need to work as hard or as long to cool the building.
  • Cool Roofs reduce the electrical power of HVAC equipment which can run less frequently and with lower capacity.
  • Cool Roofs lower air pollution and greenhouse gas emissions by reducing power demand.

How a Cool Roof Works

A Cool Roof is more than just a roof painted white. To be a Cool Roof, a roof must be treated with a specialized coating material that is lightly colored and has two unique properties: high solar reflectivity and high infrared emissivity.

Solar reflectivity expresses the degree to which a roof reflects the visible, infrared and ultraviolet rays that comprise solar energy. Surfaces with high solar reflectivity reflect more infrared and ultraviolet rays.

Infrared emissivity refers to the roof’s ability to give off its absorbed heat. Highly emissive surfaces are cooler than non-emissive surfaces since they have the ability to shed more absorbed heat at a faster rate.

A Cool Roof reduces the amount of energy absorbed by the roof which helps lower a building’s temperature and cuts energy costs.
If you have any questions please feel free to contact us with any comments.

Resources

http://www.nyc.gov/html/coolroofs/html/home/home.shtml

http://www.coolrooftoolkit.org/wp-content/pdfs/CoolRoofToolkit_Full.pdf

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