How can you reclaim green land, reduce heating and cooling costs, and control the amount of rainwater going into the sewer system? With a green roof!
Green roofs consist of low-maintenance grass or plants like sedum. Because the soil depth is kept below 4 inches, most weeds cannot survive on a green roof’s shallow soil conditions.
Green roofs work best on flat or low incline roofs, and retrofitting a green roof onto an existing house may not be possible because of the extra weight added by the vegetation. But if you are building a new house, this is a great way to save money and the environment. Green roofs cost more upfront (about 1.5-2x more expensive than a traditional roof), but they last 20-30 years longer than traditional roofing. Green roofs last longer because they protect the roof’s waterproof layer from damaging UV rays and from the day/night temperature fluctuations that can cause cracking. The green roof’s added insulation leads to 5-15% reduction in summer electricity usage.
Good for the wallet, and good for the environment! Green roofs can absorb 50-60% of the rainwater that falls on them, and also reduce the urban heat island effect. The urban heat island effect is created mostly by urban surfaces like pavement and traditional roofs, which absorb solar energy and re-radiate it as heat. “On hot days in Chicago for instance, temperatures atop the green-roofed City Hall are typically 25 to 80 degrees Fahrenheit (14 to 44 degrees Celsius) cooler than the adjacent county office building” (news.nationalgeographic.com/news/2002/11/1115_021115_GreenRoofs_2.html).
They reclaim green space, and provide a habitat for some birds. It's even possible to graze small farm animals!
Other Green Roof Examples:
The California Academy of Sciences (above) has a 197,000-square-foot green roof, covered with 1.7 million native plants! http://www.calacademy.org/academy/building/the_living_roof.php
The popular cleaning products Ecover's headquarters sports a grass roof: http://www.ecover.com/us/en/About/
Minneapolis Central Library has three green roofs, designed to manage storm water runoff on-site. www.greenroofs.com/projects/pview.php
Chicago's City Hall is also very impressive...egov.cityofchicago.org/city/webportal/portalDeptCategoryAction.do