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The Week in Green Design (11/12/05): Green Roofs

Jill Fehrenbacher and Sarah Rich write about the ongoing evolution of sustainable design at Inhabitat.

American cities have a surprising amount of wasted open space. Even in densely packed urban areas like New York City, the prime real estate atop roofs is given much less consideration than one would expect from a populace that values each square foot of space so highly. This oversight is a real shame, because there is so much that can be done to improve the local environment and quality of life, simply by fixing up a roof.

The average city rooftop is layered with black tar, a material which traps sunlight and heat, raising the temperature of the surrounding area. The heat trapped by dark, flat roofs elevates city temperatures as much as ten degrees Fahrenheit - contributing to what scientists call the "urban heat island" effect.

So what can we do about it? Read on.

Cool Roofs
The easiest and quickest solution to combat the urban heat effect is simply to turn hot dark roofs into "cool roofs" by painting them with a basic coating of light-colored water sealant. In the same way that white clothing helps keep you cool in the summertime, white roofs reflect sunlight and heat. If all the roofs in New York City were "cool roofs", the city would save some $100 million dollars per year in cooling costs.

Green Roofs
An even better alternative to cool roofs (albeit one that requires more time and effort) is to turn waste roofs into landscaped Green Roofs. Green roofs having the same cooling effect of white roofs, with the added benefits of:

  • Providing amenity space for building users ó replacing a yard or patio
  • Increasing roof life span
  • Reducing storm water run off
  • Providing noise insulation
  • Filtering pollutants and CO2 out of the air
  • Providing locally grown food (with roof-top vegetable gardens)
  • Increasing wildlife habitat in built up areas
  • Reducing heating (by adding mass and thermal resistance value) and cooling (by evaporative cooling) loads on a building
  • Reducing the urban heat island effect

    Cost & city planning
    Green roofs add so many benefits to a building and its surrounding area, itís astonishing that more roofs aren't green at this point. The biggest roadblock to our green roof future seems to be cost and bureaucratic red tape of city planning laws. Although green roofs cost more up front to install than regular roofs, the savings that they accrue over the years quickly pay off. The biggest hurdle to getting green roofs going in more places, is convincing getting city governments to change their policies and adopt programs which provide incentives to property owners to renovate their roofs.

    In this endeavor, the city of Chicago is leading the way. Chicago's Department of Environment is actually giving away $5,000 grants to any building owners who want to start a green roof project. So if you are a lucky homeowner living in Chicago, you have no excuse for not making your rooftop green!

    Meanwhile I'm waiting for New York City to wake up and get on the ball with this. If only this photograph were more than just an "artist representation"

    Frustratingly, another hurdle to green roof world-domination is the fact that ever since the "back-to-the-earth" straw bale movement of the seventies, green roofs have been associated with a sloppy, crunchy aesthetic. This is an unfair and unfortunate connotation, since green roofs can be as clean, modern, and integral to "good" architecture as glass and steel. Peter Zumthor's green roofs on the Val Thermal Baths in Switzerland are just one example of a stunning use of green roofing in contemporary architectural design.

    Others include Renzo Piano's proposed redesign of the California Academy of Science in San Francisco. Piano's green roof design features mounds and valleys of various heights and sizes, creating pockets of shade and opening vistas into the surrounding Golden Gate Park.

    The largest "living roof" in the world was designed by environmental architect William Mcdonough, and sits on top of the the Ford Motor Company's Rouge Manufacturing Plant in Dearborn, Michigan. Other notable green roofs include the international airport in Amsterdam, and the sloped green roofs of the Palais Omnisports in Paris-Bercy.

    For more information on Green Roofs check out:

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    Great info!

    I had a flash of insight a few days ago. All the empty space between skyscrapers in the city above the road. Why don't they change the transport into GRINT (Grid of Renewable Integrated Networked Transport)? Below the skyscrapers are automatic parking places.

    On top of where theres holes in the city for the crappy current roads, on top of the GRINT you replace the current road system with, why don't we building multiple layers of biomass producing hydroponics, basically making the city one big renewable building. On top of the huge building we can put swimming pools, hanging gardens, SolaPhilm, raincatchers, and mad wind turbines. All of this can be fueled by wind/solar produced electrical energy, bioFuel cells, or fusion power.

    -- - light in the darkness

    Posted by: David Spoey on 13 Nov 05

    The Australian Parliament Building in Canberra also has a pretty large green roof. The whole building is made to look as though it is carved into a hill with four large sloping portions of the 'hill' covered with grass. It's a strange, unique and striking building and truly fits the aesthetic of Australia's 'Bush Capital' that was founded a mere 80 years ago. Canberra is truly a modern city and the architects of the parliament building must have seen the pointlessness of trying to effect a Classic (Greco-Roman) feel in such a place, opting instead for a truly 20th century building.

    There sadly weren't too many pictures that came up on Google's image search but here's what I could find:

  • here's one of the green roof

  • here's one of the whole building

  • and here's one of the front facade

  • Posted by: Jesse Jenkins on 13 Nov 05

    I'm a huge fan of green roofs. Not that I've seen them, but the theory sounds excellent. Nice green rooftop patio... seems divine.

    Looking around my college campus though, most buildings have a diverse array of ac units, pipes, antennas and other miscellania scattering the rooftop. None of these are more than five or six stories tall, but I'm wondering what roof real estate is normally dedicated to.

    Posted by: Rektide on 13 Nov 05

    I have been complaining for years about the misuse of roof real estate. The most expensive floor to buy in any building is the penthouse, that is the prime real estate. But right above it, in most cases, the real estate is worthless tar and machinery. With green roofs, builders can regain some (if not all) of the real estate for selling purposes. With buildings taking up most of their land in most urban environments, builders can use roof yards as selling points.

    Posted by: don on 13 Nov 05

    This, and maybe David's idea, sort of reminds me of some old science fiction magazine pictures where all the roofs of the giant skyscrapers were used for something in addition to mere building HVAC. And rather whimsical looking autogyros would flit from rooftop to rooftop.

    Of course if we put a bunch of railways, platforms and such extending out from skyscrapers, it would plunge the streets below into darkness. Eventually it would encase the entire city into a sort of Asmovian Caves of Steel/Trantor kind of thing--everything would be one giant building.

    But I don't think the rooftop garden idea intends to take things that far. I agree. That area should be reclaimed and made photovoltaic or planted greenery.

    Posted by: Pace Arko on 13 Nov 05

    The only problem with retrofitting greenery on top is its heavy when wet. A poor soul I sorta knew went sod roof and then a rainstorm lasted a smidge too long and well he could have been laid to rest in an envelope.

    Also rooves tend to house the elevator works the cooling systems all the exaust systems and tv and sat and cell towers and finaly the wether up there often sucks.

    Posted by: wintermane on 14 Nov 05 then where do the solar panels go?

    Posted by: Alex on 14 Nov 05

    There are cities built at very high densities - as high as cities with skyscrapers - but with buildings usually no more than 5 to 6 stories, and with abundant green space. These cities are generally (but not all) in the Muslim world, and they're built around courtyards. Buildings are attached, and green space is contained within their courtyard forms. The rooftops, being lower, are more welcoming places for people. The outside spaces, being largely semi-private, are safe, quiet, and cool without air conditioning. This isn't transferable to existing western cities, but we sure are building lots of new real estate - perhaps we should look for different building forms, not just plant sod on top of the old ones.

    Posted by: David Foley on 14 Nov 05

    Wonderful ideas. Most of them are new to me. Thanks to all of you for these posts.

    Posted by: Steven Earl Salmony, Ph.D., M.P.A. on 14 Nov 05

    Can any of you think of ways we might be able to humanely restrain certain global human "overgrowth" activities, e.g., rising per human consumption, expanding predominant economic production/distribution capabilities, and increasing absolute human population numbers? Given their current scale and rate of growth, these distinctly human activities appear patently unsustainable on a small, finite planet like the one God has blessed us to inhabit.

    Thanks for all you are doing to protect biodiversity from extinction, Earth from irreversible degradation and humanity from potential endangerment.

    Posted by: Steven Earl Salmony, Ph.D., M.P.A. on 14 Nov 05

    Whether it's a cool roof or a garden roof, either is a more attractive alternative to the dark colored roofs that drive consumption of so much energy. The author of this article should have presented a slightly more balanced picture of the garden roofs downsides and the benefits of the cool roof systems. Benefits of cool roofs also include roof life extension, sustainable, reducing urban island effect while the garden roofs can add tremendous weight to the most vulnerable part of a building in addition to roots that grow where they will and if there is a leak in a garden roof, and there will be, there is no economical or precise way to locate it. Garden roofs in general have not been around long enough to have the proof statements to suggest they can actually extend the life of a roof. Good write up, just needed to be more balanced.

    Posted by: matt on 14 Nov 05


    Solar panels would become the cladding on the sides of the building in areas where there is not currently a window. Especially Southern facing parts of the building (in the Northern hemisphere).

    Posted by: don on 14 Nov 05

    The main reason for that difference between muslim and european and american cities is weather related.

    If you go to places with simular weather in america you can find some interesting roof designs BUT those places in america tend to be much less densly populated.

    Posted by: wintermane on 15 Nov 05

    Hi -- great article, terrific pictures. However, I would like to point out two omissions:

    1. The Ford Plant in Dearborne, Michigan is no longer the largest green roof in the world at 10.5 acres; Millenium Park along Chicago's waterfront now has that distinction at 23.5 acres. It is an outstanding green roof project and was a 2005 recipient of the Green Roof Awards of Excellence presented at the Third Annual International Greening Rooftops for Sustainable Communities Conference, Awards and Trade Show in Washington, D.C.
    2. The green roof industry association was not mentioned in your list of references: Green Roofs for Healthy Cities was established seven years ago to support the development of the green roof industry in North America, and now has members in the United States, Mexico, Canada, the UK, Europe, Asia and Australia. We run the annual conference in North America, lobby on behalf of the industry to get government policies and incentives incorporated into official plans, and are developing an accreditation program to set some industry standards for anyone implmenting a green roof. We can be reached at

    Thanks for allowing me the updates.

    Jennifer Sprout
    Director, Conferences
    Green Roofs for Healthy Cities

    Posted by: Jennifer Sprout on 15 Nov 05

    SORRY for the incorrect URL in previous posts. I trust the one below works.

    My comments are a bit off point in this discussion, but I hope those of you who are interested in the global challenges posed by a growing human population on Earth, will assist with creative ideas -- consonant with universally shared human values -- for compassionately regulating human over-consumption of limited resources, the seemingly endless expansion of human overproduction, and continuously increasing absolute human population numbers, all of which appear to be occurring synergistically, but unsustainably, on the small, finite planet we are blessed by God to inhabit.

    Posted by: Steven Earl Salmony, Ph.D., M.P.A. on 18 Nov 05

    Thanks Jennifer! Green Roofs for Healthy Cities is a excellent resource - sorry for the oversight.


    Posted by: Jill on 18 Nov 05



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