Walk the streets of any major American city and you can feel the heat. During the summer people sweat it out as they pound the pavement. There is no way around it, cities are hot -- in more ways than one. Not only are they up to seven degrees warmer than surrounding suburban zones, but also more and more people are moving to urban areas. By 2050, the UN Population Fund predicts that as many as two-thirds of the world’s population will live in a city.

That is a concern for the environment. City leaders from coast to coast are working to find ways to “go green”.

» READ: New York City's Plan for a Green Future

One answer may lie hundreds of feet above the sizzling sidewalk.

Up on the roof.

Click to enlarge

Green roofing is the latest trend in sustainability. However, it is more than just a garden on top of a building. As Columbia University researcher Stuart Gaffin describes, “its basically a layer of growing medium of different depths with plants, specially chosen plants that do very well in harsh hot temperatures, potentially low rainfall environments. Underneath this system is a waterproof membrane to protect any water that gets down. There’s a drainage layer to move the water around smoothly and evenly on the roof. And then there’s a root protection layer to protect roots from penetrating downwards.”

PICTURES: Seeing Green

This engineered system serves a number of functions for the building and the city. The non-profit organization Earth Pledge includes green roofing as one of its top three initiatives and after learning some of the benefits, it is easy to see why.

A green roof can:

• Reduce heating and cooling costs
• Protect the roof
• Provide sound insulation
• Create recreational space
• Aid storm-water retention
• Improve air quality
• Conserve energy

A green roof can also impact the weather. It has the power to not only keep a building cooler, but also alter the direct microclimate over that building.

BLOG: Life At The Top

“Of course in aggregate then if we were all helping our micro-climate than the whole city might have its urban heat island effect mitigated by a degree or two, which is actually a lot,” says Earth Pledge Executive Director Leslie Hoffman. Simply put, a green roof can lower summer temperatures.

GOING GREEN: Our Green Earth

A green roof does cost more than a traditional roof, approximately twice as much. However the roof is also expected to last twice as long. Supporters say the benefits far outweigh any negatives.

For more on the story, click the play icon in the video box.

Resources:
Earth Pledge Organization
Columbia University, Center For Climate Systems Research