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Recently we installed a living roof for a home in the north bay.
The above photo was taken on the day when we installed the irrigation. The plant material that you see is a mix of different varieties of a plant called Sedum. Sedum is a low growing type of flowering succulent which can withstand direct sun and whose leaves hold water. These characteristics are a distinct advantage for a green roof. We worked with a supplier who grew the plants for us during the last five months.
Given the increasing popularity of living roofs we wanted to give our readers a short synopsis of what they are, their benefits and what makes an existing roof a good candidate for one.
All the best,
 Gardeners' Guild Inc.
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What is a Living Roof?
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An extensive roof
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A living roof (or green roof) is vegetation that partially or completely covers a building or residence. Each living roof is different, but typically they have the same basic components: a waterproofing layer, root barrier, drainage layer, irrigation system, growing media (soil) and plant material.
There are two general categories of green roofs.
One type is called an intensive roof (or rooftop garden). This is heavier, more complex and is widely used for commercial buildings. It can accommodate a variety of plant material including trees; also pathways, furniture and water features. It's height can be several feet tall and it is designed for pedestrian traffic. Thus, it needs to be maintained as with any grade-level landscape.
An extensive roof is more frequently chosen for residential or multi-family housing. It is shallower, lighter and low maintenance. Plants are smaller and the growing media is about two to six inches deep. It is not designed for foot traffic. Vegetables are not ideal for this type of roof, but low care plant like Succulents are perfect for it. Plant diversity is kept low because the watering requirements must be the same. Extensive roofs are the simplest to install. In the last several years some modular green roof products have emerged allowing for plants to be grown prior to installation which expedites the installation process.
The graphic above illustrates the layers an extensive green roof.
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Benefits of a Living Roof
Reduces the volume of storm water runoff The soil on a living roof can absorb 90 percent of the rain that falls on it. This can help mitigate the cost in storm water management. The environmentGreen roof layers actually filter the rainwater, removing pollutants before the water moves on to streams or rivers. Reducing "Heat Island" EffectsIn summer heat, the temperature on a living roof can be as much as 20 - 60 degrees cooler than on conventional roofing. Saves on heating and cooling costsThe vegetation provides shade in the summer and its insulation helps retain heat in the winter. Extends the life of your building's existing roof.Potential LEED creditsThere are a number of categories for LEED that could apply to a living roof. Some of those include: Protecting/Restoring Habitat, Storm Water Design, Heat Island Effect and Water Efficient Landscaping. For more information.
It is wise to consult with a professional first to determine if your roof is suitable for a living roof installation.
Here are some considerations for an extensive roof:
- Your roof should be flat or no more than thirty degrees sloped.
- Status of any existing drainage systems and waterproofing.
- Green roofs weigh more than conventional roofing, you will also need to ensure that your building can support the added weight of the soil after a rainstorm - at least 20 pounds per square foot.
- Also - a green roof should be in a sunny location which has minimal shade.
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Largest Green Roof in North America!
The size of eight football fields, this 10.4 acre living roof was installed ten years ago at Ford's Dearborn truck plant's final assembly building. It has helped them save on heating and cooling costs. For more information.
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