Posted October 06, 2016 by Gabriel Posternak

Cool and green roofs: are they that good for our over-heated cities?

If you have ever spent a day in any major city, you don’t need me to tell you how hot it can get in the concrete jungle. During daytime, cities absorb solar energy whose heat is radiated back to the atmosphere at night. The result is sweaty, over-heated cities that have higher temperatures than its surrounding areas – basically what many have come to know as urban heat islands.

You’ve surely noticed that phenomenon by now and probably dismissed it as just another issue of living in a big city. Unfortunately, that heat is a threat for public health and for the notion of sustainability in a bigger scale. Over-heated cities increase death rates and the demand for cooling energy while also being extremely unpleasant to live in. In short, they are a problem and one that we need to address right now – especially since more and more people are moving into those very same cities.

Luckily, there are some people already working on the issue – and some of they are suggesting we should help those over-heated cities with green and cool roofs as our allies.

Why roofs, anyway?

Think about it. Roofs account for almost 30 percent of the total area of any city and they are mostly built with asphalt, a material known for its performance but also for its heat absorption. That’s why many experts think roofs are the key to tackle the problem. With enough reflective and green roofs, the amount of heat absorbed by our homes should be reduced dramatically, which would also translate in less energy use, lower emissions and more sustainable cities altogether.

Additionally, roofs usually are remodeled more often than whole buildings, so the change could be quick and virtually effortless. Well, at least in theory. Now, what happens with green and cool roofs in practice?

The Chicago example

The University of Notre Dame’s Environmental Change Initiative recently conducted a study on green and cool roofs and their effects in Chicago. They used green roofs covered with plants and vegetation, and cool roofs, surfaced with reflective materials, to test the impact on the city’s temperatures in many areas.

https://www.youtube.com/watch?v=170ceT_dvcE

The results are very interesting. While green and cool roofs actually help in mitigating the urban heat island effects on a local level, they weren’t as uniform as expected. Besides, there were some unforeseen regional effects that acted as factors in how the overall city performed. In other words, downtown Chicago saw a major drop in its temperatures in the range of 7-8 degrees Celsius while the metropolitan area ‘only’ saw a cut of about 2-3 degrees. The takeaway is obvious – green and cool roofs work better on densely populated areas.

Additionally, the difference between the temperature in Chicago and its surrounding areas was less than without the energy-efficient roofs. That impacted the strength of breezes and the overall quality of the air above the city. Though that might seem like minor things, they should be looked into, since they directly affect the temperatures of our cities as well.

So, are there benefits in green and cool roofs?

A quick look into these types of roofs might tempt you to say that green and cool roofs are extremely beneficial. Implementing green roofs on a large scale would bring more plants and green spaces to our cities, improving air quality and increasing local humidity. Cool roofs, on the other hand, are energy-efficient and don’t require watering while having a similar impact on temperature as green roofs.

Of course, we should take into account the other, more ‘invisible’ effects that could arise from implementing green and cool roofs on a larger scale. After all, cities are vibrant ‘organisms’ that depend on many factors to work and perform. City planners should be informed before passing regulations to implement these efforts.

But what YOU should learn from all this? In a domestic scale, green and cool roofs are amazing opportunities to save energy and money. They aren’t major investments and their benefits exceed their negative impact by far. Perhaps you should think about it next time you’re considering a remodel. A green or cool roof can make a true difference on how you live and you’ll be helping our over-heated cities with a sustainable effort. It might not be a huge deal but it’s a beginning!

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