As the innovation, convenience, affordability, appeal and popularity of green roofs continue to increase, so do the structural and design options for creating one. From extensive to intensive, layered to modular, seasonal to evergreen, flat to sloped, there are seemingly endless combinations of approaches for creating a vegetated roof.
Interestingly, the current issue of urban living magazine Dwell provided a very simplified (and incomplete) list of options for achieving a green roof: add several inches of soil to an existing roof; create a roof top potted garden, or; install a roof top hydroponic garden. Their description of the first method leads the reader to basically understand that you can shovel a bunch of soil onto your existing roof (as is) and start planting. Eek! As I read this I had horrific visions of thousands of gung-ho DIYers tossing potting soil onto their shingle roofs, planting gorgeous gardens and (a) watching it all wash away with the next big rain fall, (b) sobbing uncontrollably when they get the estimate for repairing all the water damage to their attics, walls and ceilings, (c) wondering why their roof is starting to sag, (d) feeling sad and frustrated by the dead plants covering the top of their homes and emanating some serious bad feng shui, or (e) all of the above.
While the Dwell options can work in the right circumstances (pots and hydroponics are a nice way to dress up a finished balcony or strong flat roof), shovelling any old soil onto any old roof is not something recommend. The weight of the soil and water, lack of proper waterproofing and drainage, and the uncertainty of the load-carrying ability of roof make this approach really risky and potentially quite disappointing. To better address all these issues, let me highlight another green roof option not mentioned in the Dwell article: engineered green roofs.
I’m not sure why engineered green roofs weren’t included in the list – especially considering Dwell has featured these types of roofs in many of their issues (including the current one – check out the beautiful fern covered roof on the Montreal home featured this month). Think Chicago City Hall, Vancouver Convention Centre, and pretty much most of the green roofs you see on new buildings in Canada, the US and Europe.
Engineered green roofs are designed to ensure that the roof structure can manage the very heavy load of the planting medium, plants and water; that the planting medium minimizes weight and maximizes efficient drainage; that there is waterproofing membrane to keep all moisture away from the actual roof (and the rest of the building), and; that the plants are appropriate for the local light, climate and grade conditions.
Within the engineered roof category, there are another bunch of choices for designers, contractors and building owners. Increasingly, the preferred approach is to go with a green roof “system” that includes pretty much everything you need – drainage, membrane, planting medium (which is a light weight, long lasting alternative to soil), etc. The components are normally installed in layers, like a sandwich. Once everything is installed, it’s time to plant. Depending on the plants and your local conditions, it could take a few months to several growing seasons for the plants to mature into the roof of your dreams.
Another “system” that we are really excited about is a modular engineered green roof system called LiveRoof. Instead of having to assemble each layer of the system, insert all the plants and then hope for the right growing conditions, LiveRoof arrives on-site as pre-grown modules that we put together in grid pattern. The modules are custom planted to your specifications and grown at a local nursery until the vegetation is mature and you are ready for install. It’s pretty rewarding to transform your roof from nothing special to something wonderful in a very short time. In addition to knowing other systems, GCB is a LiveRoof Certified installer.
To sum up here, I don’t dislike Dwell. Quite the opposite. I am really glad they and other magazines are so keen to feature and promote green building, compact design, DIY ideas and, of course, green roofs. Next time perhaps they will provide a more robust list of options that includes the safer, longer lasting solutions. In the meantime, just give us a holler if you have questions.
Also, if you are poking around this month’s issue of Dwell, take a look at their review of Print Workshop, a fantastic new printmaking book by our friends at Yellow Owl Workshop in San Francisco. Congrats to Chris on finding more ways to inspire the masses to create and enjoy things of beauty!!!