What is a Green Roof?

Green Roofs are plantings that are placed on the roof of a building. Green Roof technology is not new. Rooftop gardens are very popular in Germany. Between 1989 and 1999, German roofing companies installed nearly 350 million square feet of green roofs.

Rooftop gardens are most easily used on flat roofs. However, if designed correctly, a rooftop garden can be placed on a low pitch roof.

Green roofs are also called rooftop gardens.

Planning a rooftop garden

In order to build a rooftop garden, you will need to take into consideration the size of your roof and plant selection available in your area. Ideal plants for rooftop gardens with a few inches of depth are plants that are drought tolerant, such as low growing grasses, sedums, and catcus-like plants.

If the depth of the rooftop garden is several feet, shrubs and small trees can be used.

In most cases, it is best to hire a professional to build the rooftop garden for you. A professional should be able to work with different roofing systems, soil mixes, manufacturers & designers, and climates.

Extensive green roof vs Intensive green roof

An extensive green roof has low lying plants designed to provide maximum groundcover, water retention, erosion resistance, and respirative transpiration of moisture.  Extensive green roofs usually use plants with foliage from 2 to 6 inches and from 2 to 4 inches of soil.

Extensive green roof plants should have most of the characteristics listed below:

  • Low growth height
  • Rapid growth / spreading
  • High drought tolerance
  • Fibrous root as opposed to tap roots to protect roofing membranes
  • No special irrigation or nutritional requirements
  • Low maintenance – trimming, weeding, feeding
  • Plants shouldn’t generate airborne seeds in order to prevent the green roof plants invading other landscaping.

An intensive green roof is intended to be more of a natural landscape, installed on a rooftop.  Intensive green roofs may use plants with foliage from 1 to 15 feet and may require several feet of soil depth.

Benefits of a Green Roof?

There are several benefits of growing a rooftop garden. Some of the most common benefits are:

  • aesthetically pleasing
  • reduce city “heat island” effect
  • reduce carbon dioxide impact
  • reduce summer air conditioning cost
  • reduce winter heat demand
  • lengthen roof life by two to three times
  • remove nitrogen pollution in rain
  • neutralize acid rain effect
  • reduces noise
  • reduce storm water runoff
  • provides songbird habitat