A biodiverse green roof is not the same as a roof garden. Roof gardens involve a tremendous amount of irrigation and labor, while a biodiverse green roof is designed to be as simple and self-sustaining as possible.
The "biodiverse" part of the roof involves complementary plants that help feed each other and sustain each other.
Biodiverse Green Roofs: Two-Step Process
All biodiverse green roofs start with two steps:
- Creating a watertight roof, typically with some form of rubber roofing material that helps insure that roots will not grow through the roof and water will not seep in.
- Planning the specific plants you will use in your biodiverse roof eco-system.
In an existing structure, the traditional roof is waterproofed, and then a thin layer of insulation is installed. Next, a drainage layer is placed over the insulation. This allows for proper drainage during and after rain, and also to allow the plants' root structures to flourish. On top of the drainage comes the "garden medium" or plant medium, typically a thin layer of compost or a compost and soil combination. The medium should be no more than 1-2 inches thick.
How you structure your biodiverse green roof from here is largely a function of choice and design. You can create light frames on the roof to section off specific plants or grasses, especially if one plant among your choices is more invasive than others. You could also simply choose to mix the plants you choose.
Once you decide how to proceed, you plant the seeds you've chosen, and let nature take its course.
Maintaining a Green Roof
Biodiverse green roof maintenance is simple. Once a year you apply a thin layer of fertilizer and weed, if needed. If you chose thicker grasses to use on the roof, or a thicker-rooted herb (such as thyme, or lavender), you may need to weed out the root structures as well.
You don't need to get on your roof with a lawnmower and mow your roof (now there's a picture!), but you might need to take hedge clippers and give the roof a good trim, depending on the plants you select.
Benefits of a Living Rooftop -- Mow Your Roof?
Green roofs can help to reduce the "heat island" effect of urban areas that have large percentages of asphalt, sidewalks and shingles roofs for surface area. With the greenery of rooftop grass or herb fields, the sun helps the vegetation to grow and groundwater is filtered through the greenery.
The long-term energy benefit to a biodiverse green roof is the insulation that the roof provides. Most roofs are darker in color and absorb heat, driving up air-conditioning costs in warmer parts of the country. A biodiverse green roof helps to lower energy costs and provides homeowners with tight plots or little land to grow a convenient landscape for herbs, grasses and more.
Resources:
"Green Roofs and Biodiversity," Urban Habitats, December 2006.
"Green Roof Biodiversity: Restoring High-Rise Habitats," AIArchitect, April 2009
Melanie Zoltan - Melanie Zoltan is a former college professor and administrator who has written for About.com, PCWorld, Brain Child, Thomson Gale, and ...
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