Have you ever driven into a city from a more rural area and thought the temperature seemed a lot warmer in the city? It's not your imagination. Many cities are actually warmer than the surrounding areas due to a phenomenon called the heat island effect. This increased temperature occurs mainly due to the presence of so many dry, exposed surfaces made from dark-colored materials. These roofs, roads and parking lots absorb heat from the sunlight, rising in temperature until they are hotter than air. This heat emanates off of these dark surfaces, increasing the temperature within the city.
According to the United States Environmental Protection Agency (EPA), the heat island effect can result in a city being as much as 5.4 degrees F higher than its surroundings in the daytime, and as much as 22 degrees F hotter than surrounding rural areas in the evening. This increased temperature has a number of negative effects on the community, including increased air conditioning costs, decreased water quality and increased heat-related illness. Mitigating the issue of urban heat islands is a big task. If you own a building in a city, there is something you can do to help -- install a green roof.
What are green roofs?
Green roofs are also sometimes known as rooftop gardens. They are layers of plants grown on the rooftop. Typically, a green roof consists of a sturdy base made from plywood and a roofing membrane. This is topped with a layer of gravel or similar material to provide drainage, followed by a layer of filter fabric, and finally a layer of planting substrate in which the plants are actually grown.
Depending on the size and shape of your roof, a contractor may recommend making the entire roof "green," or only covering a portion of it in this manner. Many green roofs are simply planted with moss, sedums, or other plants that need little to no irrigation. If you have a very large urban roof, however, plans can become much more complex. There are even urban roofs that include trees and flower gardens and operate as parks.
How do green roofs mitigate heat islands?
Green roofs absorb much less heat than traditional black, asphalt roofs. They also remove heat from the surrounding air through a process called transpiration. Transpiration is essentially the process by which water evaporates from the plants' leaves; plants take heat energy from the surrounding air to complete the process.
What are the other benefits of green roofs?
In addition to making the urban community a better place by reducing the heat island effect, green roofs have a number of other benefits for the entire community, such as:
- Reduced air pollution. Plants actually remove pollutants from the air. Most cities have limited plant life, and adding plants on roofs is a good way to reduce air pollution naturally.
- Better water quality. Plants also absorb toxins in the rainwater; the runoff that falls from the roof is cleaner.
- Improved aesthetic appeal. Extensive green roofs provide community members with greenspace where they can read, relax and enjoy green surroundings.
A green roof also offers several benefits for you as a building owner:
- Reduced air conditioning bills. Green roofs don't absorb nearly as much heat as traditional black roofs, meaning you'll save on energy costs.
- A longer lifespan. The greenery on the roof protects the roof membrane from heat damage, meaning that you're likely to get more years out of a green roof than a traditional one.
If you're looking for a way to improve your urban community while also reducing your energy costs as a building owner, contact a green roofing company in your area and get an estimate. They can give you more information about each of your roofing options. You might pay more upfront for a green roof, but the energy savings, cooler urban environment, and longer lifespan of the roof make this an investment many urban developers and building owners benefit from.