The way I see it is that green roofs would have limited areas that would be suitable. Certainly most houses could not have gardens due to the pitch of the roof. Also only some commercial property would want people up on their roofs gardening.

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.

Very few "green roofs" are intended to be gardened - the vast majority are designed for zero/minimal maintenance after an initial period of establishment, their intent being only to minimize energy dispersal and reduce the structure's carbon footprint. And there ARE significant economic incentives to incorporating green roofs and other sustainable building practices. In addition to substantially reduced operating costs, accumulating LEED credits often results in tax breaks on both local and federal levels for the developers. It is pretty much a win-win situation.

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 can see one wee down side to the green roof, a much more substantial structure is required to support the far higher load. All that structure has to come from somewhere be it recycled, mined or chopped down and transported to the building site.

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

Michael

As Human Society continued to evolve, certain noted scientists/anthropologists remarked on the circular aspect, a return to origins, so to speak, as the benefits of living in caves became more obvious. *

*read that somewhere on the web, I did.

I'll move into a cave when you do, Dave!

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.

The secret to a successful green roof is, first, a flat surface, which leaves out most homes. But not city buildings.

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.

Here is a link that might be useful: Buildings with green roofs

This is the use of a green roof in the Lady Bird Johnson Wildflower Center in Austin, Texas, in a short TV clip.

Very few green roofs being designed and built now are sod :-) For one, it IS too heavy, and requires more in the way of regular irrigation, routine care and maintenance than many other roofing plant choices. Here, those tend to be very shallowly rooted, extremely drought tolerant sedums and stonecrops. The entire system is often only a couple of inches thick and uses an extremely light, soilless growing medium. The additional weight of these types of roofs is barely more than designing for snowloads in other colder climates. And they can be constructed on any pitch roof. Of course more complicated living roofs, including those which constitute actual working gardens, are certainly possible, currently exist in many urban settings and do require additional design concerns.

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.

They weren't very stable but were about the only choice in the Great Plains areas where very few trees existed.
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.

I think for urban buildings, which often have flat roofs in any case and gardening space is at a premium, it's a good idea and worth the significant extra investments and costs. In less crowded areas there are better ways to reduce environmental impact.

An equivalent of 10,000 cars removed every year isn't actually that much. I think solar panels are a much more efficient use of rooftops

But solar panels do nothing to reduce storm water runoff, they can't absorb any pollutants, have no impact on the urban heat island effect and have no ability to filter or purify water. And they provide minimal aesthetic benefit, if any at all.

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

If the new-fangled live roofs absorb little water, then they don't do much to control runoff either. The heat problem can be somewhat mollified by using light-colored and/or reflective roofing.

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

I was thinking of the new "solar paint" they are developing. I'm not much of a fan of panels either.

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

Food production does require some real soil, and good moisture. So serious weight on a flat roof as already discussed. The best design for that would be a rubber roof with a deck on it to protect it, and raised beds around the outside to keep the weight mostly over the walls and avoid such a massive roof structure. Such a roof would still need internal or external guttering and water-storage if storm-control is desired.

pnbrown

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.

I am not certain what our 4-8 inch monsoon like rains would do to a living roof other than wash everything away. Practical in some areas but not many. A living roof needs something to anchor to not just to float on. I have seen one or two suggestions for a sheet for the plant roots to go through but most plans do not allow for the plants to have anchors other than neighboring plant roots.

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.

I am not certain what our 4-8 inch monsoon like rains would do to a living roof other than wash everything away. Practical in some areas but not many. A living roof needs something to anchor to not just to float on....

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

Dan

First I think the issue of weight of heavily soaked soil would be a difficult one for a lot of people. Most people can't just rebuild a better roof that will hold the weight and drain properly.

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.

My reply to catman's objections is the same as @Oct 14, 09 at 10:50.

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

So they have built some green roofs that have worked well for at least a while? I just can't say for sure if they're good till they've stood the test of time.

Gosh, we all tend to have some rather narrow views of the world, don't we!! Living or green roofs have been around for centuries. This is not exactly a new concept although the technology has changed and advanced significantly over the years, just as it has with the rest of the building and construction industry.

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 :-)

Here is a link that might be useful: a history of 'contemporary' green roofs

I just can't say for sure if they're good till they've stood the test of time.

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

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!

Here is a link that might be useful: GW Post about Expanded Shale

The guy a couple presentations before me did a study in NYC and had several roofs with several different membrane compositions & reported their results. I don't have the proceedings yet so I don't have the particular formulations and materials, but they are all thin, flexible PVC-types of different colors. Surprisingly, in this study, the green color contributed most to cooling the roof and reducing cooling load. BTW, IIRC there are vertical walls in Oakland, CA growing food as well.

Dan

I would love to have a green roof.

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

{{gwi:155718}}

There are quite a few Green roofs in New York City, but they are mostly penthouses and such for the very wealthy. So sorry to disappoint everyone here but Green roofs are rarely done because clients chicken out because of the expenses involved. I have worked for a few architectural firms in the past. We couldn't even convince the big name sports clients to have more ecofriendly, green and landscaped parking lots, for example-such easy things like that. Pushing for LEED certification, all that is very difficult; we keep trying but many a times the client will turn down Green options to cut corners in cost.

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.

I guess it might depend a bit on your location but green roofs are not all that rare.....well, maybe in Kansas :-) In fact, they are becoming somewhat commonplace in many metropolitan areas. Oregon and Washington state are very active in green roofs and 'green' construction methods as a whole and I've been associated with two wholesale nurseries that specialize in green roof technology and the sale of plants specifically grown for green roofs. The demand for these products is strong enough that a major portion of their business is devoted to this sales segment. And judging from the green roof seminars and conferences I've participated in, there is a LOT of interest from architects, landscape architects and contractors.

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.

Here is another photo of a green roof on a chicken shed. This is in Switzerland and it was a requirement that when the owner built the chicken shed, he had to replace the meadow that was lost by creating one on the roof.

{{gwi:155719}}

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

{{gwi:155726}}

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

The grass chicken house roof is one of those things I find amusing with the whole idea or sad. The chicken yard is surrounded by a green meadow. Why does only the roof must be maintained as meadow? To me it seems to be only a nice nod to the idea of preserving the growing things in the area. But only a nod so they could say look at us we did something great when they actually destroyed more than their little patch.

Gardengal, sorry to continue to disagree, but green roofs are rare for most cities except for Seattle, Vancouver, Europe, Korea. Green roofs are very! common in Europe. Seattle is at the forefront of green architecture, hence the difference in mentality. I worked for the most prestigious U.S. sports architectural firm in the U.S.. I loved working at that firm. We had lots of major projects worldwide too. It is not easy to convince certain states as well to go through Green Technology. I don't mention particular states because I have to be very careful not to get my firm in trouble either. You see certain U.S. states that could really benefit from solar energy for example because of the intense sunlight and heat have always resisted green technologies. LEED is not exactly easy to convince because contractors want immediate results and even though benefits can come within just 2 years, they only want the immediate pay-out! Literally....

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.

Actually, I must continue to disagree as well:-) I don't think you are aware of the facts behind this technology nor how rapidly it is progressing and becoming commonplace. Seattle is by no means on the forefront of green roof activity - we are well behind Portland and Vancouver BC in this regard - but the real hotbed of activity is in the midwest. Chicago has more green roofs than any other US city - over 200 and covering more than 2.5 million square feet. Dearborn, MI has the largest, 10.4 acres covering the Ford Motor Company truck plant. Minneapolis, Philadelphia, Baltimore, Washington DC, Raleigh NC, Atlanta, New York City and Toronto are all very active green roof areas as well. And then of course there are the dozens of green roofs scattered across California, both commercial and residential.

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.

I just returned from a trip that included the CA Academy of Sciences in San Francisco. Their green roof has several places that have angles that approach 45º.

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

If anyone considers 200 green roofs as a lot they should visit the northwest. Many of the areas I have visited their have even more than that and I am not counting the cedar shingle roofs that have moss and other wind blown plants growing on them. I love the look but without having lots of fog no moss on my roof.

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.

A living/green roof can be constructed in any climate - there are several extensive examples located in India, Israel and other parts of the mideast......pretty arid areas. Typically the choice of plants is fine-tuned to the purpose or location so that they will be drought tolerant and require minimal (if any) maintenance, but irrigation of green roofs is also just as common. You have a pretty good example of one right there in Kansas City, the KC Central Library.

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.

Here is a link that might be useful: KC Central Library living roof

Oak Hammock Marsh

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

Lloyd

Sedum and other C4 plants are the common treatment where humidity doesn't cause one to be called 'mossback'.

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

What is the advantage of a green roof that must have drip irrigation to survive? Most of the time the KC library roof is only open for events so unable to view but I will check on it next time I am there.

What is the advantage of a green roof that must have drip irrigation to survive?

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

Dan