Green roof construction

Description

Green roofs are composed of several layers (waterproof membrane or existing membrane, root barrier, drainage layer, filter fabric, growing medium) that support the growth of plants and other vegetation on top of a roof.

Types

There are two main types of green roof systems: extensive and intensive.

1. Extensive green roofs have growing medium depths of 10 cm to 15 cm (0.1 m to 0.15 m), maximum structural weight loads of 250 kg/m², and vegetation is primarily limited to sedum spp or commonly known as stone crop.
2. Intensive green roofs have growing medium depths greater than 15 cm (0.15 m), no maximum structural weight load and various plant types can be incorporated including native flowers, trees and shrubs.

Within these two types of green roofs are two installation type systems:

1. Modular system: green roof component layers are fused together as a moveable modular block system that can be linked together with other green roof blocks to form the green roof. This type of system typically forms an extensive green roof type and are used where roofs are sloped and flat.
2. Layered system: all components' layers are loose laid as individual layers. This type of system can form both extensive and intensive green roofs and used typically on flat roofs.

Component description

• Vegetation free zone: separates the green roof perimeter from the roof perimeter and other structures on the roof (e.g., vents), that is kept devoid of vegetation and natural debris.
• Root barrier: often a clear plastic sheet, the root barrier layer protects the water-proofing membrane from root penetration and degradation by microbial activity.
• Drainage layer: provides void space for excess water to drain from the growing media that is either stored for later uptake by plants or allowed to flow to roof drain.
• Filter fabric or geotextiles: are used to retain growing media and prevent migration out of green roof system
• Growing media will vary according to the green roof system/product installed but is generally designed to be porous and lightweight with adequate fertility and drainage capacity to support plant growth and allow for absorption and infiltration of water.
• Vegetation: Green roofs rely on vegetation (i.e., sedums/succulents, grasses, herbs, wildflowers and for intensive green roofs, shrubs and trees) to intercept, absorb and evapo-transpire stormwater. Vegetation can be installed as mats or as plugs or pots based upon the green roof design.
• Overflow outlets: Flows exceeding the storage capacity of the BMP are conveyed to an adjacent drainage system via an overflow outlet structure and the roof drainage system.
• Irrigation System (if applicable): Most green roofs will require periodic irrigation, especially during the first 2 months of the establishment period.
• Leak detection system (if applicable): leak detection systems should be used to periodically check for the presence of leaks in the water-proofing membrane.

A thin layer of vegetation and growing medium installed on top of a conventional flat or sloped roof, also referred to as living roofs or rooftop gardens.

Surface runoff from at-grade surfaces, resulting from rain or snowmelt events.

Best management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls.

A system flow of gully inlets, pipes, overland flow paths, open channels, culverts and detention basins used to convey runoff to its receiving waters. City of Toronto 45 Wet Weather Flow Management November 2006

Human application of water to agricultural or recreational land for watering purposes. City of Toronto Wet Weather Flow Management November 2006 47

Human application of water to agricultural or recreational land for watering purposes. City of Toronto Wet Weather Flow Management November 2006 47