Types of Green Roofs
What are Green Roofs?
A green roof system is a 'contained' green space on top of a human-made structure. The extension of the existing roof includes a high quality water proofing and root repellant system, a drainage system, filter cloth, a lightweight growing medium and plants. Green roofs can be installed using modular sections or created at the site.
Although green roofs are more expensive to install, they last twice as long as a normal roof and confer many more benefits to industries and communities.
Green roofs can provide a wide range of public and private benefits.
Green roofs provide the building owners with a proven return on investment and a significant opportunity for social, economic, and environmental benefits, particularly in cities.
However, in North America, green roofs are a vastly underutilized technology and there is huge potential for market expansion. Although efforts of several industry leaders have been made, the technologies are still poorly understood, unlike in Europe where green roofs have become very well established. Currently, there is a multi-million dollar green roof industry in Germany, France, Austria and Switzerland. The industry continues to experience growth, both in millions of square metres of green roofs and in the market for green roof products and services. In Germany, for example, the number of green roofs constructed increased from 9 million square metres in 1994 to 13.5 million square metres constructed in 2001.
This has been a direct result of government legislative and financial support
In BC, the Community Charter and Local Government Act allows vegetated roof systems. However, there should clearly be policies enacted to increase the number of green roofs built in Vancouver, and more specifically, at the SE Marine Drive site.
Green roofs typically fall into two categories:
1. Extensive Green Roofs:
- What is it?: Low-maintenance ground-cover system
- Where is it ideal for? Large flat-roof buildings and apartments and sloped residential roofs.
- Vegetation planted:: Desert grasses and succulent plants are embedded in three-six inches of lightweight growing media.
- Maintenance:After one year, they do not require watering although annual spring weeding of tree seedlings brought in by birds is needed.
- Example: The Vancouver Convention Centre will have 2.4 hectares of very low maintenance green roofing in preparation for the 2010 Olympics.
2. Intensive Green Roofs:
- What is it? Fully landscaped roof top gardens that can accommodate many uses
- Vegetation Planted: Diverse plants and trees are planted in 8-12 inches of soil amid features such as walkways, railings and lighting. Parks, playgrounds or vegetable gardens are possible.
- Maintenance: Requires regular maintenance.
- Example: In Greater Vancouver, Electronic Arts has a rooftop park, while the Vancouver Fairmont Hotel grows herbs on its rooftop for the hotel kitchen
Intensive vs. Extensive?
- Although intensive green roofs may require extra costs, they may confer more benefits
- Extensive roofs are less expensive to build and maintain
- Depending on how thin the profiles are, some extensive green roofs may not require extra structural support
- A cost-benefit analysis for an intensive roof must be done on a project-by-project basis
Policy | Extensive Green Roof | Intensive Green Roof |
Soil Depth | 8-25 cm (3-10 in) | 25-100 cm (10-40 in) |
Weight | Less | More |
Utilization | Less Diverse | More Diverse |
Species | Less Diverse | More Diverse |
Opportunity for Urban Agriculture | No | Yes |
Low Maintenance and Irrigation | Yes | No |
Accessibility | Low | High |
Code Compliance | Minimal | Walkways, railings, lighting, access |
Sources:
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