Vegetated roof assemblies
ethan_TFGStudio
| Posted in Energy Efficiency and Durability on
I am quite familiar with vegetated roofs (aka green roofs). Some advantages include for membrane durability, reduced insulation, and perhaps some insulation. Other green qualities are habitat and owner connection with nature. I’ve been looking around GBA and can’t find much discussio discussion about vegetated roofs. They seem like a good fit over many of the well insulated for systems discussed here.
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Replies
http://buildingscience.com/documents/insights/bsi-052-seeing-red-over-green-roofs
https://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/do-green-roofs-temper-urban-heat
Ethan,
Here are some links to GBA articles:
Lessons Learned on a Living Roof
Do Green Roofs Temper Urban Heat?
There Are Many, Many Green Roofing Choices
Design a green or living roof system
GardenScapes Vegetated Roof System
How to Insulate a Flat Roof
How do you include an eco-roof into a home energy audit?
Ethan,
In addition to the GBA articles that I linked to, I urge you to read the Joseph Lstiburek article that Malcolm linked to (Seeing Red Over Green Roofs). In that article, Lstiburek explains why vegetated roofs aren't very common: they are expensive and they don't provide much R-value.
That said, if you want to install a vegetated roof, the GBA articles I linked to will give you preliminary guidance toward designing such a roof.
"If energy is your deal, add more insulation to your roof and install a reflective membrane and be done." Is energy the only ideal? I also look at beauty, habitat preservation, stormwater management, and site integration.
I have worked on one project in which the architect had designed a sleeping porch to look over an EPDM membrane roof. We designed a vegetated roof to improve the view. But an added bonus of vegetated roofs, if designed correctly, is to improve the longevity of a roof membrane.
So many of these "green" houses (as in Green Building") have no green... they are "warts on the prairie" as I read somewhere here. I've started reading through the suggested articles, but I feel like we might be ships passing in the night. I think I can do a vegetated roof for less than $110/sf.
One Idea I have is to do the vegetated roof portion over an unoccupied space below (carport, patio, etc).
Ethan,
It's possible that installing a vegetated roof will extend the life of the roofing membrane. But if there is even one membrane installation error, finding and correcting the membrane installation error will cost much more than it would have without the soil and vegetation.
A PV array is another way to shade a membrane roof; by shielding the membrane from UV rays, the PV array should also extend the life of the roofing membrane.
All that said, green building is a matter of the heart as well as the brain. If your heart wants a vegetated roof, by all means build a vegetated roof.
Ethan,
I provided the link to Joe Lstiburek's article not to discourage you but because I think he hits the nail on the head. From a completely building science perspective there are probably easier ways to achieve what green roofs do. But while we may pretend otherwise, houses are overwhelmingly cultural artifacts. As Martin and Joe say' green roofs, like all sorts of other things we include in our homes, speak to us. That may well be a more than adequate reason to include them in your projects.