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a primer on green roofs: part two

February 1, 2008

zora naki

Types of Green Roofs:

Green roofs have the same basic structure. They consist of the following layers:

  • structural support
  • roofing membrane
  • membrane protection and root barrier
  • insulation
  • drainage layer with another root barrier
  • growing medium
  • vegetation

The main difference lies in the amount of growing medium and what you can grow.


Cob House Green Roof, Stanley Park, Vancouver BC - (C) BCITExtensive green roofs have 3 – 6 inches of growing medium that will support mosses, sedums and other low-maintenance native plantings.

After being established, they will generally thrive with little to no maintenance and should not require watering, although spring weeding of tree seedlings may be necessary. These roofs are well-suited to buildings with inaccessible roofs.

A growing number of companies sell preplanted containers suitable for extensive green roofs. These usually contain a mix of hardy, native plants such as sedums, grasses and wildflowers that are appropriate for your climate. These modular systems can be installed directly onto the roofing membrane.


Intensive green roofs have a more substantial 8- 12 inches of planting material, and will support everything from flowers to trees, depending on your structural constraints.

Suitable for the flat roofs of office and condo buildings, intensive roofs may incorporate vegetable gardens, parks, play structures, etc. Because of the increased needs of the plants, an irrigation system may need to be incorporated into the design, as well as access points for weeding, fertilizing, and general gardening. Landscape design services could add considerable value for the end-users of the roof.


Extensive and intensive roofs are only the beginning. Depending on your roof, you may decide on a hybrid combination of the two to best suit your needs. If your roof is more complicated (i.e. has a greater slope than 2:12, has a number of peaks and valleys), get professional professional help -either in the planning or the installation phase.

Private Residence, submitted to: your roof just isn’t suitable for planting, consider the green wall approach. There are some fantastic installation possibilities and everyone gets to enjoy the results of your labour…

Ideas for green walls:

Patrick Blanc: Vertical Garden
Parabienta Green Wall by Shimuzu Corp.
G-SKY photo gallery of installations
Blog post: Ellis Hollow self-installation
Wall-to-Wall Gardening

Next up: how to decide on what’s right for you and additional resources
Before: benefits of green roofs

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