You may have heard of the term "urban heat island." It's really just a fancy way of saying that, in certain areas of a city, heat energy concentrates to raise the temperature.
Cities are, for the most part, manmade and thus don't possess the same characteristics to dissipate heat that naturally forming structures and ecosystems enjoy. Typical cities, for instance, don't grow as much vegetation, which provides shade and the cooling effect of evapotranspiration. The materials that constitute a city—concrete, asphalt, etc.—absorb more of the sun's solar energy. They heat up and warm the air around them. The very geometry of most cities is unnatural. These materials that don't dissipate heat very well, also bounce short-wave radiation between the relatively close, tall buildings. And remember: these buildings are filled with people. Anthropogenic heat emissions from heating and air conditioning units, other electrical use, etc. contribute to warmth in the surrounding air. Clear skies and calm winds will only amplify these effects in an urban heat island (UHI).
What can be done to lower these heat elevations? We can't raze the city and start from scratch. We also can't ignore the heightened heat index either.
According to the US Environmental Protection Agency (EPA), elevated summertime temps increase energy demand for cooling. This can lead to rolling brown- or blackouts. The higher energy consumption also leads to more burning of fossil fuels, which release air pollutants and greenhouse gas emissions into the atmosphere. Heightened temperatures can also result in the formation of ground-level ozone, an unhealthy concoction of noxious gases.
What we can do is adapt.
Green roofs, a growing trend all over the world, are one of the most comprehensive answers to alleviate heat from UHIs. They can grow, flourish atop city roofs and bring the temperature down in the following ways:
- Evapotranspiration: Green roofs combine plants' power of transpiration—the process of moving water up from roots to pedals and leaves—and evaporation—conversion of water from liquid to gas—to remove heat from the air. The water sucks up heat energy as it evaporates from plants and soil (growing medium) into the now cooler atmosphere.
- Green roofs, soaked and swollen like a sponge after a rainstorm, store large amounts of heat in the retaining water. The heavy moisture regulates temperature fluctuations.
- Green roofs, when dry, act as an insulator, decreasing the flow of heat through the roof. Less heat thus escapes from the building into the air.
- Green roofs provide additional benefits, filtering storm runoff and absorbing pollutants like CO2. If you think about it, reducing CO2 in the air also reduces heat (global warming) in the long run. The absorptive quality of a lush green roof also acts as an effective sound barrier for noisy city streets.
- Furthermore, green roofs can optimize the performance of rooftop solar panels. According to livingroof.org, the cooling effect of a green roof keeps the surrounding air around panels at a temperature within which the photovoltaics can operate most efficiently.
- An elastomeric liquid waterproofing membrane can help complement a green roof system
September 22, 2017
Playing with fire
Waterproofing on roofs and decks has traditionally been done using open flames or the application of heat (for example, using hot rubberized asphalt systems and torch on membranes). However, the risk ...
February 27, 2018
SILCOR® liquid waterproofing projects
When two of London’s largest international airports embarked on their own expansion projects, they both needed to find durable solutions for waterproofing podium decks. These podium decks serve multip...
October 15, 2018
Waterproofing for a green roof
Studies abound that green roofs reduce the effects of urban heat islands. They're also far more aesthetically pleasing than a basic, blacktop roof. Green roofs provide shade, comfort and a place to en...
October 18, 2017
Top Five Reasons to Use Liquid Waterproofing
Architects are increasingly specifying liquid waterproofing membranes to extend the life of podium decks and roofs. Contractors are also finding they prefer these easy-to-install solutions over sheet-...
November 15, 2017
Make the most of outdoor space
Developers are increasingly finding novel ways to maximize outdoor space, creating inviting terraces and roof decks that offer sweeping views as well as more living area for a variety of uses. This ma...