How does one construct a green roof?

There are 2 methodologies that can be applied. The growing medium can be placed directly on the specific underlay required for green roofs or alternatively the plants can be grown in modules / trays. The Module approach is beneficial for difficult applications for example on corrugated roofs and where one wants an instant effect or needs mobility. Both these types require the following:

  • The roof must be checked by a specialist structural engineer to ensure that the existing roof can take the additional load of a green roof.
  • Next a Green Roof specialist/ designer must be consulted before design.
  • An additional protection layer is applied on top of the existing roof membrane.
  • A drainage layer is placed on top of the protection layer (not required for Module application).
  • Specialised soil layer is carefully placed on top of the drainage layer (The soil layer is a light weight, well drained, high moisture retention layer compiled of Vermiculite, Perlite, and well composted growing medium).
  • Only then is the vegetative layer planted.

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The specialised plant layer

Characteristics of the ideal vegetative layer in the application of green roof:

  • Must be drought resistant and heat tolerant.
  • Preferably low growing and self seeding (so as to replace themselves from seed when stressed from heat and water fluctuations).
  • Wind resistant.
  • Plants that can survive in extreme growing conditions.

TIP: When selecting plants, ensure that the plants have been hardened off / acclimatised to withstand the harsh conditions mentioned above.
Examples of some of the plants used on a green roof

Please download this file to read more on how to construct a green roof:

Green Roof Applications PDF (580kb)

More DIY:

How does one grow food on a roof?