with concrete and other built structures. When one thinks of cities, nature doesn’t typically come to mind. However, with green roofs, roofs on buildings that contain living plants, nature is returning to cities in a number of new and innovative ways. Because green roofs have a variety of benefits for modern cities, they are are being built in many large cities around the world today and are a great innovation of our time.
The following list shows some of the top benefits that green roofs can provide to cities and other places.
- Green roofs save energy.
Conventional roofs are a large source of building heat loss in the winter and heat gain in the summer. Because green roofs help to to insulate buildings, they also help to reduce building energy demands and their associated energy costs for heating and cooling.
To compare how much energy is required by a building with a green roof with buildings that have dark roofs or white (reflective) roofs, check out the Green Roof Energy Calculator from Portland State University.
- Green roofs reduce stormwater runoff.
Rainwater is stored by the green roof substrate and then is used by plants. The plants then undergo transpiration and respiration, where the water is released by into the atmosphere as water vapor. Any small amount of rainwater that is not absorbed gets filtered by the plants before it runs off the roof.
When rainwater flows through green roofs, the green roof reduces and slows down the flow of stormwater, assisting with stormwater management problems that are common in cities.
- Green roofs help to reduce the urban heat island effect.
The urban heat island effect occurs when the temperatures in cities increase more than the temperatures in surrounding rural areas. This difference in temperature is due to the reduced vegetation in cities and the presence of large amounts of concrete and other impervious urban surfaces that collect and radiate high amounts of solar heat during the summer.
Because plants undergo dew and evaporation on a daily basis, plants on green roofs and other urban outdoor surfaces can help to cool cities and reduce the excessive heat that accumulates in cities due to the large amounts of concrete. Plants also absorb sunlight that would otherwise be converted into heat.
- Green roofs are great places to grow a community garden or an urban farm. Many cities are now realizing the benefits of using previously unutilized space as a place to grow edible plants. Many restaurants are even getting in the action by growing produce right on their own roof, giving their chefs the freshest ingredients available. Some green roofs even house beehives!
- Green roofs provide opportunities to increase the presence of nature in cities.
In most urban environments, available habitat for wildlife is greatly reduced when compared to many rural areas that contain more of their natural habitat.
Vegetative roofs can provide habitat for birds and insects and act as “stepping stone habitats” between the isolated habitat patches that exist in the middle of cities. While many green roofs are similar to a more natural type of lawn in appearance, some green roofs even have trees and shrubs, like this one in Toronto, Canada, where birds could potentially live.
- Green roofs have aesthetic benefits.
Green roofs and other urban green spaces add beauty and charm to the built environment of cities.
- Green roofs improve air quality.
Plants on green roofs and plants that are present on other surfaces can capture pollutants from the urban air and filter out gases from the air that could potentially be toxic to the environment and human health. Green roofs can also help to reduce dust, particulate matter, and smog in the city air.
Also, because green roofs help to moderate the temperature of both buildings and of the overall urban area, there is reduced energy demand, and therefore helps to reduce the overall amount of pollutants generated by power plants, including greenhouse gas emissions.
- Green roofs increase the usable spaces in cities without increasing the urban footprint.
Green roofs can be used to add usable space to a building, and can provide community value, such as through recreational spaces like parks, community gardens, or commercial spaces like display areas and restaurant terraces.
- Green roofs create local jobs.
When green roofs are being built and maintained in cities, new opportunities arise in order to meet the demand of green roof-specific manufacturing, the production and growth of plants for the roofs, and for green roof design and maintenance. All of these opportunities require qualified people to work and meet that demand, thereby creating an entire new industry and the many associated jobs that go with it.
- Green roofs increase the lifespan of roof materials.
On a green roof, the vegetation helps to reduce the exposure of the underlying roof materials to fluctuations in weather and temperature, as well as UV radiation from the sun, which can lead to wear and tear and damage to roof materials over time.