Topic 4

As it was mentioned in previous modules, green roofs are internationally placed in two main types:

  • Intensive – parks and gardens, including urban agriculture.
  • Extensive – natural low maintenance green roofs.

Of course, there are some cross overs between the categories.

The key characteristics of intensive and extensive roofs are summarized further on.

Intensive gardens

  • Need frequent maintenance, just as a park or garden needs to be tended on a regular basis. 
  • The degree of maintenance for intensive green roofs depends on what has been planted.
  • Because these types of intensive green roofs have deeper soils, they are heavier than extensive green roofs. They therefore need to be installed on a much stronger structure.
  • Urban agriculture on green roofs would be considered an intensive green roof, as they need regular maintenance, relatively deep soils and a certain amount of irrigation.

Extensive gardens

  • Extensive green roofs tend to have a thinner growing medium than intensive green roofs. They therefore require less maintenance.
  • As they are lightweight, they are easier and less costly to install. In general, they do not require irrigation although some irrigation may be required initially.

  • Sedum mats have a base layer of polyester, hessian, or porous polythene, depending on the supplier. A 20 mm layer of growing medium is laid and sedum seeds or cuttings are spread across it.

  • Substrate based green roofs generally have 80 mm of substrate. The substrate sits on the filter sheet, drainage layer and protection layer. The vegetation layer consists of sedums and wildflowers.

Brown roofs for biodiversity: the original concept was to use recycled brick and concrete from a local recycling plant. Over the years, the brown roof idea developed into the green roof designed for biodiversity. Roof substrates have about 20% organic material and only native species are used for this purpose. Find out more.

Introduction on how to build a self-designed green roof:

  • An unused roof may be the perfect spot to cultivate fruits, vegetables, flowers, trees, and shrubs. However, experts should be invited to come and install a waterproof membrane, root barrier material, and structural support.
  • Opting for a container garden (or using raised garden beds) is simpler and less expensive. Just like the containers themselves, the soil inside must also be lightweight. Instead of heavy garden soil, opt for a soilless potting mix that includes ingredients such as peat moss, vermiculite, and perlite.
  • Container plants need frequent watering, as they don’t hold moisture long due to evaporation. It should be considered how the appropriate watering schedule will be kept. Will it be an irrigation system installed or a hand water each plant one or two times daily.
  • Different plants have different light needs — some require full sun while others prefer partial shade. With a container garden, there can be rotated pots to prime locations as needed.

Here are some instructions and practical examples on how to create a green roof: