Why Roof Gardens Rock!


There are many benefits of a rooftop garden beyond the fact that they can be quiet retreats. They add another dimension of green space to an urban scape without taking up an extensive area of land in densely populated places. In some European countries such as Switzerland, bylaws have been passed that new buildings must be designed to relocate the greenspace covered by the building to their roofs. Existing buildings must also comply with the bylaw by greening at least 20% of their rooftops.

These relatively simple changes to rooftops can greatly benefit our urban areas. Here are some examples of the advantages of rooftop gardens:

• Green roofs can help in the absorption of carbon dioxide and help reduce air pollution.

• Storm water runoff, flooding and water pollution can be reduced.

• The building and surrounding area’s aesthetics will be enhanced and property value could be increased.

• Economically, there are no additional land costs.

• Temperatures around the building can be lowered in the summer.

• A building can be further insulated from the cold in the winter.

• The roof life can be extended by protecting it from various weather conditions.

•Heating and cooling bills will be reduced.

• The rooftop garden space can be used for food production.

ROOFTOP GARDEN TYPES

There are two types of rooftop gardens and depending on the structural design of your roof, one might be preferable to the other. One is the extensive rooftop garden, often inaccessible and the other is the intensive rooftop garden, which is accessible to people.

1. Extensive rooftop gardens:

• Generally lightweight gardens.

• Require little or no maintenance.

• Vegetation acts like another layer of the roofing material and usually covers the entire roof.

• Can be installed on both flat and sloped roofs.

• Depending on climate and the amount of rainfall, can grow a variety of hardy grasses, wildflowers, mosses and sedums.

• Use drought-tolerant plants that will go into hibernation if exposed to harsh conditions like wind and sun exposure and/or under-wateri.

• Since they are not generally walked upon, guard rails, exit requirements and access need not be a concern. If they will be walked on, these aspects need to be considered. 

2. Intensive rooftop gardens: 

• Allow for a more diverse plant selection such as perennial flowers, trees and shrubs (all of which can remain in containers over the winter) and the potential to grow food.

• Are subject to building and zoning codes, especially with respect to public safety issues, hence the need for proper exits, guard rails, and lighting.

• Generally installed on flat roofs with the vegetation either covering the entire area or in containers and raised beds.

 • A stronger roof structure is required due to the added weight of people accessing the garden as well as higher soil and container weights, decking and trees all adding to the weight impact to the roof.

• More maintenance is required because of the greater variety of plants.

• Other considerations for an intensive rooftop garden include condition of roof, structural and weight capacity, access, cost, irrigation, and drainage. 

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