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Green roof energy savings

Hello,
As a project for school, I am looking at installing a green roof on a building on the Vanderbilt University campus. We are looking at installing an extensive (6" deep soil or less, with simple plant growth) for a 1500 square foot area that is currently black top. It is a single story building, that is in use 24/7 by students. What would be the estimated yearly energy savings for such a project? This information needs to be approximated for the proposal. Thanks and blessings

Asked by Andrew East
Posted Wed, 12/05/2012 - 00:44
Edited Wed, 12/05/2012 - 06:00

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3 Answers

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Andrew,
If you are aiming for energy savings, a green roof (vegetative roof) is a waste of money. The R-value of soil is about R-1.4 per foot, so your proposed soil layer (6 inches) has an R-value of about R-0.7. That's insignificant.

If you want to improve the energy performance of a roof assembly, it makes much more sense to add insulation rather than dirt. For more information on the absurdity of vegetative roofs, see Seeing Red Over Green Roofs.

However, you may have other reasons to install a vegetative roof -- perhaps you want to have a pleasant place for a picnic. That's fine. But it's impossible to justify the project from the perspective of energy savings.

Answered by Martin Holladay, GBA Advisor
Posted Wed, 12/05/2012 - 05:56
Edited Wed, 12/05/2012 - 05:57.

2.
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Hello Community,

A green roof is a building roof covered in vegetation. Beneath the vegetation is a waterproofing membrane or layer that prevents water and soil from entering the interior of the building. These gardens are designed to make more efficient use of natural energy conservation techniques. By incorporating a green roof into building design, the building becomes part of a localized ecosystem.

Best Regards,
John Marrison

Answered by John marrison
Posted Wed, 12/05/2012 - 23:29

3.
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John,
Thanks for your comments. I must say, however, that I have no idea what this sentence means: "These gardens are designed to make more efficient use of natural energy conservation techniques."

There is a technique to save energy -- what technique? The technique is natural -- OK, what does that mean? And this technique (the natural one) can be used efficiently or inefficiently, presumably, but the construction of a rooftop garden allows the (unnamed) technique to be used in an efficient way.

I think.

Answered by Martin Holladay, GBA Advisor
Posted Thu, 12/06/2012 - 04:22

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