Link here.

It would also provide urban dwellers space to grow their own produce and avoid some of the price of trucked-in or "artificially-ripened" fruits and vegetables.

In principle it is a good idea and it's great that some companies are doing it. Maybe if there was tax incentives more companies might go along.

I would expect to see much more activity with green roofs and commercial construction. It is far harder to convince average homeowners to incorporate sustainable building practices into new construction or remodelling as they don't often fit our preconceived notion of how the typical family residence should look. And they do tend to require a higher upfront investment, as well. And there are fewer residential developers and contractors that are LEED certified, although that is changing, especially with the upper scale, custom housing market.

I like the idea however, talk about a quiet home!

Michael

*read that somewhere on the web, I did.

As noted, a green roof can only work on very low-pitch roofs. In a heavy rainstorm the root-mass of the sod cover will absorb an immense amount of water. This will obviously create a huge weight until it transpires and evaporates. There is significant extra cost in building a structure strong enough to resist the maximum weight without the deflection that could eventually lead to leaking.

Given that pretty much all residential and business buildings use some amount of electricity and heating/cooling, it might be greener to build a conventionally lightly structured roof with either heat-reflective roofing or solar-collection via pv and/or water heating.

Second, the growing medium must be very light-weight, a lot of vermiculite and perlite mixed with substances that provide for root growing.

There must be sufficient drainage from the growing medium AND the roof surface.

It can be done, particularly with new construction -- I've been reading about it for years, and as in many innovations, Europe led the way, maybe because there were and still are so many sod-roofed houses in that part of the world, where at least grass could grow.

The effect of a green roof goes far beyond the energy savings associated with the structure it covers - there is also the moderation of the urban heat island effect, absorption of pollutants, water filtration and purification and mitigation of storm water runoff. These are often considered to be more significant, especially in urban areas, than the reduction in energy costs.

Sod houses, while inexpensive to construct, are difficult to maintain. The sod would be cut from the prairie into slabs approximately 2 feet long, one foot wide, and 6 inches thick, which would be stacked grass side down to form the walls. The roof would generally be made of boards covered with sod. In some instances, the window "glass" would be made of paper soaked in lard. Generally, on the roof, the sod would be placed grass side up, thus precluding erosion of the roof. However, if the sod was placed grass side down on the roof, there would be less problems with a constant drip of dirt and mud from the ceiling. In some instances, to catch the dirt dripping through the ceiling, muslin would be suspended to catch the dirt. In more modern versions of the sod house, this problem was solved, as noted below, by the use of either a conventional roof or placing of tar paper beneath the sod. Because of the weight of the sod, particularly after a rain, a center post was normally needed to help support the roof. The packed dirt floors would have to be watered down regularly. Beds would have to be placed on boards in order to prevent the legs from sinking into the dirt floor. In the spring, the sod roof, six to eight inches thick, would have to be replaced. Without constant maintenance, one's house was apt to erode away in the rain at a fairly rapid rate.

The weight of the sod on the roof always presented a danger of roof collapse and the walls made a convenient place for vermin to den. The owner of one Colorado soddie complained of "mouse season," and others complained of rattlesnakes denning in the walls. The roofs would leak. Heavy rains caused a drip of mud from the ceiling. Indeed, it has been said that if it rained outside for one day, it would rain inside for two. A few soddies, however, were improved and made permanent by plastering of outer walls and the addition of shingle roofs, thus, protecting the house from melting away. Others had the interiors improved, again by plastering, wall paper and wooden floors.

Often, "efficiency" is in the eye of the beholder :-)

You don't like rows of solar panels? I don't much either. Reduce energy usage - that's the answer to all the problems.

Not that I don't like the idea of green roofing, I just don't think it is that significant of a tool for fighting global warming, but it is an incredibly good use of space. Think of all the local fresh produce that can be grown on the rooftops on one city alone. That by itself can save tons on gas

Take a look at Introduction to Living Roofs, posted earlier. It describes the structure of green roofs, and they aren't as difficult as you might think.

Questions I would like to find answers to are how often do you have to replace any growing medium. I am aware that the decomposing plant tissue will provide some.

If the roof developes leaks such as after a hail storm how are the membranes repaired? All ripped of and start again or are there sealents that will allow patches.

Much of the information is on new roofs setting up etc. What about in 20 years.

All these issues mentioned have already been dealt with, years ago. Not a problem.

Dan

Second, the cost of the growing medium, fertilizer, plants, irrigation, and everything else would be a LOT. This isn't realistic except in large buildings where companies would have enough to afford such a project.

Third, I can just imagine the government giving out tons of taxpayer money for people to build green roofs. But I don't think it would go that far.

I still like growing things in the ground. They're going to have to find better methods if they want to reduce CO₂. I personally am very skeptical and don't consider myself a believer in global warming. I think we should cut back on pollution, and invent reliable green products, because I know a lot of stuff we do definitely isn't doing any good for the environment.

Just my thoughts. I would rather have a solar roof with an in-ground garden than a "green roof" that's a pain to maintain.

That is: I recently presented a paper at an international Urban Heat Island conference, and green roofs were a component of several presentations. None of the purported problems found in the thread above were real problems on the ground, so to speak.

And even though incentives and non-restrictive regulations are not in place everywhere, green roofs are a growing demand as the heating/cooling load reductions and waterproofing elements have positive net benefits. And the stormwater credits available in just a few places help comply with national stormwater regs as well.

HTH.

Dan

FWIW, there are industrial/commercial living roofs that have been established and in place since the early 60's. As with many newer building concepts, Europe has been in the forefront and you can see examples of these in Germany, Austria and Sweden. Japan is very big into green roofs as well and Tokyo has regulations mandating a specific amount of vegetation that must be incorporated into new construction (and I don't mean inground plantings!). There is also a lot of interest in living roofs in the mideast and some of the most extensive and elaborate current examples can be found in places like Dubai, which btw also has regulations in place requiring at least 30% of the roof surface area on new construction be 'green'. There is less documentation on residential applications, but suffice it to say, they too have been in place in Europe for generations and there are US examples that are at last 20 years old (excluding the pioneers' soddies).

Perhaps many are in a time warp where the term 'green roof' means only a sod covered cabin :-) I think before too many more negative comments are generated about the impracticability of these "new-fangled" living or green roofs, some responders should take some time and educate themselves on the current technology so they can at least enter into discourse intelligently. It's pretty darn easy to nay say when you haven't a clue what you are talking about. Do a Google search on living or green roofs and see all the many examples and get an idea on the technology involved. And maybe terms like 'soil' as a planting medium will disappear from this discussion :-)

That's OK - they are being designed, permitted and installed at an ever-increasing rate across the entire planet, despite your being unsure. It ain't rocket science, and the membranes are the only new technology being employed. The sedums and other CAM plants have been around for millions of years.

Dan

I'm curious about the newer membranes and construction techniques for green roofs. Here's one report about a green roof (in Virginia, I believe). Though the membrane separating the growing medium from the building roof isn't described, the growing medium is one I haven't read about before:

[It is comprised of]...80 percent puffed [or expanded] shale, 15 percent organic material such as compost and five percent sand. The four-inch-thick growing medium is contained in a series of components that include a waterproof membrane, drainage system and water-retention layer. The typical green roof weighs 20 pounds per square foot.

"When rain falls, the roof retains 80 percent of the water before it's saturated and the rest goes through the system and off the roof," says Charlie. "It's really remarkable."

While on a leisurely jaunt to find information on newer materials (got sidetracked as you might guess), I found this information about vertical walls being constructed in Paris, which can also be used to help cool the environment and human living spaces as well. They're stunning when designed for beauty as Patrick Blanc has done in these slide shows!

Here are some still photos of his work. We'd do well to expand our creative thinking about how we garden and interact with plants in our environment. Not all of them are required to grow in tidy flat sprawling places. Many do surprisingly well in vertical environments as long as they have light, water, and nutrition. Soil itself is a minor consideration under those conditions.

So there is more than one choice for combining construction materials and techniques if people want to cool their buildings with natural resources, such as on rooftops or walls.

Thank goodness for creative artisans who combine the best principles of engineering, botany, and beauty!

Dan

This is on a roof on a building in NYC, which I saw on the National Geographic site....

Also another issue is having in-house architects and engineers who both specialize in these experimental technologies. Change is eventual but it is also a very slow evolvement that may take decades. In Seoul Korea and places in Europe, green roofs really take off. In the U.S. green roofs are a rarity....

Prairiemoon that rooftop and some of the key images in this thread are not built rooftops-- they are conceptual 3D drawings made by computer. I am a 3D animator/modeler and therefore I can immediately recognize 3D generated images. But a few are real and it makes me happy to see the green roofs in architectural magazines. But again, they are quite rare.

FWIW, my former employer is currently involved in the installation of the largest green roof in Seattle - almost 8400sf. This downtown condo/hotel complex has qualified for LEED silver certification.

This second one is on a hospital roof in Switzerland, where foliage is mandatory on new flat roofs....

In this country, I thought that there was more interest in the Chicago area?

LEED is a gradual process. But with the economic fallout, all the architectural firms are going through massive layoffs so everything can get delayed as well. Less funds, less research, cancelled projects...but I am glad that at least the current administration does its very best to continue to address environmental concerns.

This is not an isolated movement nor is it a flash in the pan technology. Modern green roofs have at least a 30 year history in this country. There is a very active and increasingly growing community of architects and contractors specializing in this approach and scores of companies dedicated to the technology and materials to build and plant living roofs - a simple search through Google will turn up literally hundreds of them. One of the incentives that stir this on is the same you claim to be a deterrent - the downturn in the economy has made it even more appropriate to pursue this technology. Initial costs may be higher to design and install a living roof compared to a conventional roofing system, but this is easily offset by the extended lifespan, the lower maintenance and the energy savings realized over the life of the structure - an investment in a living roof actually saves money.

And there are numerous studies that show LEED standard buildings are almost the same cost these days as less-efficient buildings. Green buildings are not a problem either and mostly the old-school developers who don't know anything but old school are not on board.

Dan

One of the difficulties in many areas are the city codes and home owners associations.

I would like some pointers since a number of posters have declared that information on green roofs is common place. From what I have seen it is common place where water forms airborn moisture not in the dryier sections of the country.
I would be especially interested in the steeper roof information.

Currently codes only allows on new construction but the few I have seen in this area look like mine fields after our storms and the various animals that like to dig.

I have looked for information for green roofs in the middle of the country but very few have information that would work here. I am in Kansas City MO.

Having lived in the PNW all my life and being pretty familiar and involved professionally with this technology, I'd love to know where all these many hundreds of green roofs are located :-) We do have quite a few and more coming online all the time but the PNW is well behind other parts of the country, especially parts of the midwest that, outside of New York, have really been the drivers of this movement. btw, we're not really as wet here as most non-natives seem to think - Seattle receives virtually the same average annual rainfall as KC, right around 36 inches.

A local Manitoban green roof facility. (page three talks about the green roof)

Lloyd

The presentation about NYC that I mentioned upthread had the sedums + other small xerics, and the museum video for the CAS roof had two botanists talking about the native volunteers that they were finding (including invertebrates) amongst the sedums after only a year.

Dan

Lower energy usage, ameliorated temperature range in the envelope, stormwater runoff ameliorated, urban heat island reduction, etc etc etc.

Dan