Green Roof Types

Green Roof Lawn and Drainage Materials

Commonly referred to as Growing Media or Soil Substrates, the growing medium used is an essential part of the green roof system. Careful consideration and planning is required during the design phase of a green roof build and a local growth expert should be consulted in order to develop the best system for your needs. The proper build-up will allow for successful establishment and lasting vegetative growth in your local area. The growing media needed to facilitate a healthy green roof will be determined by the type of vegetative growth.

Before the growing media is selected there are other layers of the green roof system which play major roles in the functionality of the roof. To better understand the full use of a green roof system, we have broken down the layers here.

Green Roof System Layers

The various materials used in the different layers of a green roof provide a variety of ecological functions including: structural integrity, water retention, biological diversity and climactic improvements. The different layers of a green roof include:

  • Root barrier
  • Protection layer
  • Drainage layer
  • Filter layer
  • Growing medium

Both the root barrier and protection layers are used to protect the roof structure from potentially damaging roots and water. The drainage layer allows excess water to drain from the soil preventing pooling.

The drainage layer can be created using different lightweight aggregate materials such as gravel, clay tiles and lava rock. They can also provide additional functions for the green roof other than just drainage. They can also be used to increase the size of the root growth zone and provide space for an aeration system. To assist in excess water drainage rubber or plastic modeled drainage elements are often included in this layer.

The filter layer is made to ensure the drainage layer and water outlets do not become clogged with silt or other particles as a result of water draining through the soil. The filter layer separates the substrate layers (growth media) from the drainage layer below and captures the humic particles and organic materials from draining out, leaving them for the plants.

Growing Medium is the foundation for your plant growth and depending on the types of plants you want to have on your green roof the depth of the soil will need to be taken into consideration. Some types of vegetation require more soil depth for root establishment. The soil can range from under 6 inches (extensive) to a few feet deep (intensive).

Get more information about extensive, semi-intensive, and intensive green roof systems.

Often light-weight mineral materials that have a high water retention capacity with good permeability are preferred. The aggregates, organic matter and sand used in the growing medium help to give the soil structure its integrity, allows for water retention and drainage and provides the balance needed for a healthy growing environment. However, when choosing the growing media to use on a green roof there are a few criteria to be aware of:

  • Grain Size
  • Organic Material Proportions
  • Frost Resistance
  • Structural Stability
  • Wind Erosion Resistance
  • Water Retention Capacity
  • Water Permeability
  • Aeration
  • Nutrient Content
  • pH-Value

When choosing growth media it is highly recommended that you seek consultation from a growth specialist, contact us today to learn more.

Once the green roof system is in place, your foundation for growth is set and you can begin to plant and reap the benefits of a green roof!

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