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LiveRoof: Green Roof Fire Test (YouTube)
Green Roof posts (GBLU)
[I am on vacation this week in Phoenix and then Kansas City so I bring you GUEST POSTS! I met each of the guest authors somewhere along the way and asked them to contribute. Hope you enjoy.]
By Linda McIntyre
Does the notion of plants on a roof seem bizarre, even dangerous, to you? If so, that’s understandable--there aren’t a lot of green roofs in the US yet. But their numbers are growing, because green roofs--relatively simple installations usually featuring low-growing herbaceous plants, not park-like roof gardens with furniture and trees--can be useful functional tools when properly designed, installed and maintained.
A green roof has a waterproofing membrane like any relatively flat roof. Above the membrane, plants grow in a layer, usually four to six inches deep, of mostly mineral-based medium that looks like gravel, not soil. A drainage layer comprising coarse aggregate or synthetic sheets ensures the system will drain properly after it reaches field capacity, and fabrics are available to protect the membrane from roots if the material isn’t naturally repellent. These layers make up the green roof assembly. Think of a ballasted roof with plants growing among the stones.
Why put a green roof on a building? It can help control stormwater runoff (a big and growing problem in cities), reduce energy costs (especially for air conditioning), and provide amenity space for employees or residents (if a building’s loading capacity allows for such access, a green roof assembly can provide a cost-effective garden). The green roof assembly, when properly designed and installed, protects the membrane, extending the lifespan of the roof. It can earn LEED points and make a building more marketable. If built on a mass scale, green roofs can mitigate the urban heat island effect that makes densely-built cities so uncomfortable in hot weather. A green roof aggregates benefits in a way that other approaches, such as reflective white roofs, which also save energy, can’t. And it will almost certainly look better than a black tar roof.
Maybe you’ve seen a couple of green roofs and been unimpressed. Not every green roof is flamboyantly beautiful, and not every project is successful. There’s no “Consumer Reports” for green roof components, and trial and error is unavoidable with any new technology. Green roofs are common in Europe, but still relatively new here, and we have a more variable climate and a different building culture. Research, project data, and the accumulation of experience are helping to fill knowledge gaps and making it easier to design and install successful green roofs.
A green roof isn’t the right choice for every building. It’s always going to cost more, and installation will always be more complicated. Especially for the first year or two of its life, it will require more maintenance than a conventional roof. But, more and more, it’s a choice worth considering.
Linda McIntyre is a writer specializing in environmental and urban issues. She is working with nurseryman and consultant Ed Snodgrass on a book about designing, installing, and maintaining green roofs, to be published by Timber Press in 2010.
A few weeks ago, Toronto announced a mandatory green roof requirement, which my fellow bloggers dutifully covered. When I read about the green roof mandate, I thought of another Canadian city with a similar program.
You remember the Vancouver Catch-22, right?
Many British Columbia jurisdictions, including Vancouver, began mandating green roofs. Simultaneously, the Homeowner Protection Office required homeowner's insurance covering roofs for new developments. A resourceful government official with the Homeowner Protection Office did some digging and sent out a letter emphasizing that insurers would not issue policies covering green roofs.
In the end, the Homeowner Protection Office had to call a meeting with the insurers, the building industry and government officials to find a solution. Quite embarrassing.
When I read about the Toronto green roof mandate, I thought to myself "good for Toronto, they ironed out all of the insurance and liability issues associated with green roofs."
Marks says, however, that green roofs built to the Toronto construction standard won’t be able to pass Underwriters Laboratories of Canada’s CAN/ULC S107-03, Methods of Fire Tests of Roof Coverings. “Under the flame-spread test, they shoot a flame across the top of a traditional roofing membrane,” says Marks. “There isn’t one green roof that will pass that test — the vegetation will burn, and the City of Toronto has been aware of this.”
Marks notes that the insurance sector is generally reactive to emerging issues, not proactive.
“The insurance industry hasn’t caught up with this yet,” he says. “They may need to experience some losses and claims before clueing in.”
I am no engineer but I am pretty sure grass catches on fire if you shoot a flame at it.
The green building industry is a brave new world. How long will it be before the insurance industry can assess the risks associated with green roofs and projects?
Photo: Earth Hour Global
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