ELEMENTS OF GREEN

ROOFS

Extensive Green Roof

  • Shallow growing medium (soil) between 2 and 6 inches

  • Less structural support

  • Limited plant diversity with less intricate root systems

  • Less investment and little maintenance once established

  • Requires minimal maintenance after the first year

  • For roofs without occupancy or capacity for gathering

 

Intensive Green Roof

  • 6+ inches or deeper growing medium (soil)

  • Greater weight-bearing capacity to support deeper growing medium and heavier plants

  • It can support a larger variety of plants and trees

  • Can support raised beds

  • Higher initial investment and more intensive maintenance

  • May require an irrigation system

  • It may be accessible for residents to socialize, with appropriate access and a Certificate of Occupancy.

Typical Green Roof Layers

 
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Vegetation 

The type of vegetation will vary depending on a roof's other qualities and microclimate. Sedum varieties are the plants used most on green roofs because they require little water and maintenance. Deeper substrates allow for a wider variety of plants to be planted.

Growing Medium (Soil)

Soil for green roofs must be lightweight, porous, and contain nutrients. Consider adding shale, perlite, ash, volcanic rock, or other porous materials for optimal water retention and compost, organic fertilizers, and slow-release amendments, and/or mulch appropriately and as needed.

Drainage Layer

The drainage layer guides water runoff during and after a rainstorm towards a drain or gutter. It is designed to ensure that plants may use stormwater for longer periods of time. An irrigation system for supplemental water may also be needed, depending on the vegetation used.

Insulation

Insulation may be inserted above or below the waterproofing membrane to provide additional cooling, noise absorption, and lower energy costs.

Membrane Protection & Root Barrier

The flexible material is placed on top of the roofing membrane to protect against roots perforating the roof and causing leaks.

Waterproofing Membrane

The waterproofing membrane protects the building against water leaks and may extend the longevity of the roofing membrane.

Structural Support

This refers to the underlying structure of your building and how much load (weight) it can hold. The weight of the entire green roof layer assembly, including plants and the water required to saturate the vegetation, should be considered when assessing what your building's structure can hold. Green Roofs with public access and recreational spaces have additional weight-bearing requirements.