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Green Roofs

Keith Bowers
President, Biohabitats, Inc.

I visited the green roof at the California Academy of Sciences in Golden Gate Park in January and was pleasantly surprised! Surprised to see that medium to contain the plants on the steep slopes of the roof are coconut husk trays and surprised to see a wide variety of plant species native to the San Francisco Bay region. Rana Creek Living Architecture, the consultant and installation contractor for the living roof did a fantastic job collaborating with the architect Renzo Piano and the challenges of the roof to come up with a planting medium a plant pallet that supports the native biodiversity of the region. While I am all for green roofs, I get discouraged and frustrated by many of the products being marketed and plant material being used in the name of being ‘green’. Instant green roofs consisting of plastic trays filled with 3” of soil and planted with three varieties of non-native sedum – come on! Is that truly being sustainable? If we are going to create living roofs, let’s do it right! I know cost is an issue, it always will be; but what about the costs of losing biodiversity, or the costs of manufacturing more and more plastic, or the costs of not providing enough soil to at least begin to resemble a sufficient soil profile for soil microorganisms (and ground dwelling insects) to start colonizing and supporting native plants. Let’s push to make green roofs truly ‘green’ and truly ‘living’!! What do you think?

What do you think? Click on the comment link below to see what others are saying and to add your voice to the discussion.

10 comments

  1. Polly Bart says:

    I couldn’t agree more. Plastic trays create zillions (technical term) of linear feet of edge condition, which plants don’t like much, not to mention air spaces close to the roots which get too cold. If you lay drainage mats in three foot squares, it is just as possible to remove a section if needed for checking the roof. Plus, laying separation and protection fabrics and drainage mats over the whole roof as the first thing you do protects the roof membrane while you’re working on the plant medium and planting, so it’s less likely there will be damage to the roof membrane and less likely you’re ever going to need access below the plants anyway.

  2. Nicole says:

    I haven’t seen the coconut husk trays before – that sounds much better than the plastic/metal products I’ve seen out there. If there isn’t too much slope, I think green roofs that just use media over membranes and drainage mats require the least amount of material. As for soil depth and quality, green roofs are by nature pretty poor soil quality because the media is designed to be light weight but not light enough to blow away first and foremost. Too much organic material ends up being too heavy, but I think as more green roofs are put on new buildings, I hope structural engineering will evolve in some creative ways to accommodate green roofs that resemble what would have been beneath them pre-construction more.

  3. Joseph Weidle says:

    I agree that shallow container “green” roofing is pretty much typical of most American’s view toward nature. They want to bully it into a corner, and if a small, three-inch deep, tray on the roof is where we’re all going to bully it to, then all the more convenient. Just don’t tell me I gotta water it up there, right? This is disheartening, in the face of how much change all American’s need to make in their daily lives. There is a positive side here. Seeing how decent intention (having “appropriate” vegetation above/near your dwelling) becomes poor design (container plantings)is proof that environmentalists message to the average American consumer is still NOT clear enough. Back to the drawing boards all.

  4. Suzanne says:

    At a conference I recently attended one speaker classified green roofs as two types, extensive (ie the shallow ones that support sedum as the main growing medium) and intensive (ones that can support a variety of diverse plants). He focused more on the extensive due to the extra structural support needed for the intensive, and basically said the only reason to do an intensive roof was to have a variety of plants for asthetics. I would have to disagree, it is also important to have the deeper soil matrix, because the more plant diversity you can have, the more varied of a habitat you can support. And, especially in some settings the native plants need a deeper soil to survive.

  5. Allegra Bukojemsky says:

    A few links
    A good article on the California Academy of Sciences roof in Metropolis can be read online http://www.metropolismag.com/story/20080917/part-2-the-green-roof

    There is also a good article in the January issue of Landascape Architecture Magazine about green roofs with a focus on native planting and habitat potential – and ultimately the establishment and maintenance success of doing it this way. An online preview can be found here http://archives.asla.org/lamag/greenroofs.html

  6. Julie E. Gabrielli says:

    Great article, Keith. We’re doing our part to dispel the myths about greenroofs, too. Please see our latest post: http://www.goforchange.com/2009/03/19/4-myths-and-1-important-truth-about-greenroofs/

  7. Mark Rylander says:

    Keith is right on!
    Anything worth doing is worth doing well and mediocre green roofs will never be well-loved.

  8. olyssa says:

    yup. just saw a rana creek presentation. the coconut trays may also be starting a micro-economy where they are produced….nevertheless-in my opinion, you can’t really go wrong when it comes to improving current roofing practices. i mean, when was the last time these were updated? have you seen penn state harrisburg’s dr. shirl clark’s research documenting the toxins in traditional building materials? i’m not sure she included tar roofs in her study but does anyone want to know what comes off these? i feel sorry for the poor people who install them…

  9. San Diego Roofing says:

    If we are going to create living roofs, let’s do it right!

  10. Roofing Contractor Phoenix says:

    I completely agree. I've seen some roofs put up with grass sod on them. Come on, lets get real here. That stuff lasted about six months, then died. Worst thing was, it was a taxpayer paid roof.

    I wonder how much money the consultant that recommended that got paid…

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