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As “sustainable architecture” becomes a familiar term to many, we’re starting to hear a lot about green roofing. It’s a concept that seems to have an awful lot going for it, and — added bonus — it looks really cool, to boot (especially from a Google Earth POV). Via Ecogeek, here’s a quick primer on just what they are and how they work.
First of all, there are two kinds of green roofs:
• intensive, which are between two and four feet deep and support the growth of all kinds of plants and even some small trees, but require a great deal of structural support, because they’re really heavy, and
• extensive, the most common kind of green (or “vegetated”) roof, which are about four inches deep at the most. Many kinds of grass and drought-resistant plants can thrive at that depth, which also naturally limits weed growth and tends to self-regulate. (Naturally, their weight is also a lot easier to support.)
The benefits
There are many, but a few of the most compelling include
Keepin’ it cool:
Green roofs keep the roof cooler, which helps to reduce the heat-island effect, which contributes to cities being hotter than the surrounding countryside. This can be beneficial to the building in reducing its summertime cooling load.
Longer roof life:
Green roofs also protect the roof membrane from sunlight, which breaks down the roofing material. Having even a couple inches of soil helps to greatly extend the life of the roof, and a longer lifespan means less material ends up in landfills from re-roofing buildings after the membranes have failed.
Greatly reduced stormwater runoff:
In some cases, this can help reduce the size of stormwater pipes, and the amount of stormwater that needs to be treated by municipal water treatment. In a light rainfall, a building with a vegetated roof can have no stormwater runoff at all.
Everybody gets a yard:
In cities where concrete rules and green space is at a premium, how cool would it be for everyone to have a little park of their own on the roof? You can BBQ up there, stretch out for a nap in relative peace and isolation, and even, as some have done, graze farm animals!
The drawbacks
Right now, the main drawback is expense. It’s definitely pricey to convert an existing “normal” roof to a vegetated one; the extra load necessitates extensive surveying and architectural rejiggering (and architects drive fancy cars for a reason). Cost is less of an issue with new construction.
Picture credits:
1) Green roof in Oswego, Illinois by Greg Robbins. Greg Robbins on Flickr
2. Goats grazing on a roof in Wisconsin, from Driftless Media on Flickr
Nice! But I wouldn’t want to mow it.
posted by Miss Cellania on 8-22-2007 at 7:22 am
Chicago appears to have a number of green roof installations, including for city buildings. Irrigation may also be an issue for green roofs, unless there is enough annual rain to support the plant material.
posted by john biggs on 8-22-2007 at 8:03 am
It suprises me that with all the constant wetness and traffic (ie. goats, human with lawnmower) that the roof lasts that much longer.
posted by stew on 8-22-2007 at 8:15 am
Actually, the shallower roofs — of the 2 to 4-inch variety — don’t really need mowing. The grass just doesn’t get that tall.
posted by Ransom on 8-22-2007 at 8:58 am
If you planted native grass, it would need way less watering and mowing. A lot of people around here plant native grass for a lawn because it saves them hundreds of dollars in irrigation costs. And some of it looks prettier than general lawn grass anyways….
posted by Amanda on 8-22-2007 at 9:34 am
bugs!! yuk!
posted by ami on 8-22-2007 at 2:07 pm
I agree with miss Cellania, don’t you have to mow it? That job would suck, not to mention be possibly dangerous.
posted by John Brown on 8-22-2007 at 5:24 pm
Nope, it doesn’t need mowing.
posted by Ransom on 8-22-2007 at 7:32 pm
This house needs some ivy to grow around the walls to make the entire thing covered in green.
posted by Christian on 8-23-2007 at 12:53 am
“and architects drive fancy cars for a reason”
Well, if you want to call my rusty ‘94 Plymouth Voyager Minivan with flames painted on the side fancy……
A Michigan Architect since ‘88, with a 6-figure income if you include the numbers AFTER the decimal point…
posted by Greg S. on 8-23-2007 at 7:03 am
In 1996, I took a trip too Anchorage, Alaska. We got into downtown Anchorage and low and behold they had a visitor stations in the middle of downtown. All the visitors stations throughout Alaska has the grass roof. They were mowing and edging the roof. It was not only cool to watch but, the shops were so majestically beautiful. I would do this to my house in a heart beat. It also retain heat in the winter. They also have community gardens. Something I wish every city offered. :O)
posted by hullmomma on 8-23-2007 at 8:07 am
Ransom,
Do you happen to read Plant Services? Particularly the August 2007 issue? Because I just received that issue yesterday and it had information on Green Roofs for Healthy Cities and all that stuff. Spooky how I learn about green roofs and then log on to _floss and learn about it again!
posted by Lindsay D on 8-23-2007 at 10:24 am
The roof of the building my office window overlooks in the Boston’s Seaport area is a green roof that uses a non-irrigated 5-inch deep, pre-vegetated mat which contains sedum plants.
posted by A.Non.E.Mous on 8-24-2007 at 9:15 am
In addition to a vegetated roof, there are a couple other options to reducing urban heat and doing good for our environment. There is a post on www.getwithgreen.com (under roofing category I think) that talks about materials that we can all use that are more eco-friendly…thus reducing the amount of asphalt we dump into landfills yearly.
posted by David on 8-31-2007 at 11:18 pm