Creating a Rooftop Garden

A building with a roof that is partially or completely covered with plants is known as a green roof, eco-roof, vegetated roof, or living roof. The three types of green roofs, which were developed in Germany in the 1960s, are intensive roofs, semi-intensive and extensive roofs. No matter the type, these rooftop gardens have many environmental benefits, including lowering air temperature, absorbing rainwater, creating a habitat for wildlife, and filtering pollutants and carbon dioxide out of the air.

Techniques
Creating a green roof can be achieved using a tray system or a built-up system. These systems consist of layers used to protect the building structure and to support growing vegetation. They may include a number of materials such as thermal insulation, gravel, a moisture blanket, wood chips, compost and top soil.

Starting from the structure, the layers in a tray system, which is used for extensive and semi-intensive gardens, are the insulation, vapor barrier, waterproofing membrane, and pre-planted trays. The layers in a built-up system, which may be used for all three garden types, are the structure, roof membrane, insulation and vapor barrier, filter fabric, drainage board, root barrier, protection fabric, planting soil and plants.

Garden Comparisons
Since intensive gardens are similar to those found on the ground, a thick layer of soil may be needed wherein you can grow most any type of plant, including large plants and trees. This type of rooftop garden, which requires high maintenance and can have a soil depth of eight to over 30 inches may only be installed on a concrete structure because it is heavy, having a dry weight of about 40 to over 100 pounds per square foot.

Semi-intensive roof gardens, which require limited maintenance may be installed on concrete, steel, or timber structures. Plant options for this type of green roof, which has a soil depth of five to eight inches, are sedum, moss, grass, herbs, flowers, and shrubs. The dry weight of semi-intensive gardens is about 25 to 40 pounds per square foot.

On the other hand, extensive roofs, which have limited list of compatible plants and a soil depth of two to five inches, may also be installed on concrete, steel, and timber structures. The best plants for extensive gardens are those with a high drought tolerance, such as sedum, moss, and grass. When dry, extensive gardens, which are low maintenance, weigh about 10 to 25 pounds per square foot.

Challenges
The correct waterproofing membrane system, root barrier, and drainage layer need to be used to prevent water leakage from drainage backups or possible root puncture. These could lead to roots penetrating the waterproof membrane or damaging the building's interior. This can be avoided by conducting a water flood test after applying the waterproofing membrane. Moreover, consult with a structural engineer when creating an intensive or extensive green roof as these require greater structural support. Other challenges include attracting wildlife that may lead to an infestation of pests, the possible need for an irrigation system, and determining whether creating a green roof is subject to local regulations and government fees.

Do you have experience with green roofs and what are the challenges you faced?