While at the American Planning Associations 2009 National Conference in Minneapolis, Minnesota, I was able to attend a conference session on green roofs in urban areas, and this post has been created with information from that session, as well as more sources.
Green roofs are a simple concept, and they date back to the time when humans were first learning to farm. Green roofs are simply roofs planted with some type of vegetation, or a growing medium. They are meant to replace the vegetation that was (or will be) displaced by the footprint of the house. They are also called “living roofs” and I will discuss the benefits of the roofs below.
Many people see the urban rooftop as a missed opportunity to grow things, increase solar reflectivity, fight the urban “heat island” effect and absorb (or in some cases, clean) rainwater. There are two types of green roofs, extensive and intensive. Along with this, there are benefits beyond the strictly environmental. Green roofs have a longer life span, and can reduce heating and cooling costs of the building. The extensive roofs are much heavier and can support a wider variety of vegetation than the intensive counterpart.
There have been many people calling for increasing green roofs, and there are a few great examples out there. Ford Motors has taken an interest in the green roofs, recently covering its truck assembly plant in Dearborn, MI with a green roof. Below is a section of the plant roof, obtained from greenroofs.org
The City of Chicago, IL is also becoming a leader in green roofs in the US. Many corporations are beginning to give green roofs a serious look due to their low maintenance costs and longer life span which is estimated to last ~ 2 times as long as a traditional roof.
Lets do a cost comparison between a green roof and a traditional (asphalt) roof for a 2,000 sq ft house.
Estimates put the cost of a green roof at $5-10 per square foot, and according to improvenet‘s calculator, a roof in the zip code 82070 will cost ~$3,000-4,000 dollars, and has a lifetime of approximate life span of 20 years. Clearly, a green roof is more expensive, costing ~$10,000 for the same size roof. However, we need to take in the replacement cost, as one wouldn’t replace the roof on a house they were not planning on living in for a while. So, in 20 years when your asphalt needs to be replaced, your green roof will still be going strong.
If you are of the unfortunate case that you need to replace a roof when you buy the house and plan to stay in the house for a while, you could easily replace the asphalt roof 2 or even 3 times during your tenure in the house (although I hope you are not that unlucky). The replacement cost of the asphalt comes close after the second, and will eclipse after the third ($12,000 v $10, 000). Or, using the lower estimates, would put it at a measly $1,000 difference. Factor in the heating and cooling savings you’ll get, and your payback period will get even shorter. If you’re ambitious enough to garden up on the roof, then you can recoup faster with food savings.
After reading about green roofs, you may think “well, if the last so much longer and the cost is comparable, then why aren’t more people (like you) doing it?”
Well, that’s a question I cant answer, but maybe you can, in the comment section.
Thanks for reading!
For more information, see www.greenroofs.org
Questions? email me at info@sustainablelifeblog.com
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I think green roofs are a great idea and an innovative technology to improve cities healt and people wellness!!
i’ve recently visited the site http://www.greenroofs.gr and i find it very informative about green roofs!!