"A green roof is a roof of a building that is partially or completely covered with vegetation and soil, or a growing medium, planted over a waterproofing membrane."
The following are some of the environmental benefits of a green roof:
- A green roof releases oxygen and absorbs carbon dioxide which helps in reducing global warming.
- The soil and drainage mat in a green roof retain water when it rains.
- The collected water passes through the green roof more slowly so it avoids flooding during a storm.
- The water going through the green roof has been biofiltered which cleans the water.
Listed below are the cost benefits of a green roof:
- A green roof can absorb sound better so it reduces noise within the building.
- It cools the house and can reduce electricity costs when cooling down a building.
- Green roofs last 2X to 3X longer than standard asphalt roofs.
The design and construction of a green roof involves putting on many layers:
- A waterproof membrane is placed directly on the roof to prevent water leakage.
- Next, there's a drainage mat made of polystyrene sheets which has little cups which retains water for plants to absorb.
- Then, there's a soil filter fabric which allows water and air to flow through but holds on to the soil. And a mesh layer that will decompose to help control erosion.
- Edging is put on the perimeter to create a retaining wall for the soil and garden.
- Finally, good soil; preferably something mineral oriented that is lightweight and retains heat.
- You can also put on an erosion control blanket to keep soil in place until plants get established.
Other things to keep in mind when thinking about creating a green roof:
- You may need to add additional bracing so the roof can support the weight of the soil and other materials that will go on it. For instance, a 4 inch deep green roof could way 25 pounds per square foot.
- Also, you'll need some sort of hoist to lift the bags of soil to the roof.
Source: Article by Debbie Cafazzo titled "From sloping garage roof to elevated landscape"
