Inspection and Maintenance: Green Roofs

Inspection & Maintenance Guidance of Green roofs best management practices. These specialized roofs are specially engineered and designed to support the growth of vegetation while protecting the structural integrity of the roof, aiding in helping to cool the building and effectively infiltrate, absorb and retain precipitation (TRCA, 2018).

Overview

Green roofs are engineered rooftop design features that allow the growth of vegetation on rooftops and have numerous benefits. These LID BMPs can also be referred to as vegetated roofs, rooftop gardens or eco-roofs. A green roof acts like a lawn, meadow or garden by intercepting and absorbing a portion of the rainwater or snowmelt that falls on it. The typical layers of a green roof (in ascending order from the roof surface) include a water-proofing membrane, drainage layer, lightweight growing media layer and the vegetation. Excess water that is not absorbed by the growing media or vegetation is collected by the underlying drainage layer, directed to outlet structures and conveyed via the roof drainage system to another BMP or the municipal storm sewer system. A portion of the water absorbed by green roofs is returned to the atmosphere by evaporation and transpiration by plants. Green roofs are typically designed to retain precipitation from small to medium-sized (e.g., 5 to 25 mm rainfall depth) storm events. Overflow outlets are necessary to safely convey flows from major storm events.

Generalized cross-section view of a green roof showing key components and common layers that make up this LID BMP (TRCA, 2018)

Some of the benefits of green roofs include:

• The ability to reduce the quantity of pollutants and runoff being discharged to municipal storm sewers and receiving waters (i.e., rivers, lakes and wetlands);
• Growing media and plants retain pollutants deposited from the atmosphere and reduce metals and other pollutants from conventional roof materials transported by runoff;
• Improve the energy efficiency of the building due to their insulating properties;
• Reduce the urban heat island effect;
• Can provide food and shelter for pollinators;
• Can provide aesthetic value as attractive landscaped features.
  

Key components of Underground Infiltration Systems to pay close attention to are the:

• Filter Bed / Growing Medium
• Vegetation
• Protective layers
• Irrigation System
• Overflow outlets

Associated Practices

• Intensive green roofs contain greater than 15 cm depth of growing media, can be planted with deeply rooted plants (e.g., shrubs and trees) and can be designed to handle pedestrian traffic.
• Extensive green roofs consist of a thinner growing media layer (15 cm depth or less) and are typically planted with.
• Blue roofs are systems that temporarily capture rainwater using the roof as storage and allow it to evaporate and/or to be used for non-potable requirements (i.e. irrigation, toilet flushing, truck washing) and ultimately offset potable water demands.

Inspection and Testing Framework

Maintneance of the Green roofs filter bed and vegetation composition/condition being performed by staff (TRCA, 2018).

Visual Indicators Framework - Green Roofs

Component	Indicators	Construction Inspection	Assumption Inspection	Routine Operation Inspection	Verification Inspection
Perimeter
	BMP dimensions	x	x		x
Growing medium/filter bed
	Green roof structural integrity		x	x	x
	Standing water		x	x	x
	Filter bed erosion		x	x
Vegetation
	Vegetation cover	x	x	x	x
	Vegetation condition		x	x
	Vegetation composition	x	x	x
Overflow outlets
	Overflow outlet obstruction	x	x	x	x

An example of a soakaway under construction with a newly installed monitoring well. To ensure performance assessment and infiltration testing can be conducted efficiently over the life cycle of this LID feature, the well condition must stay in good condition and be repaired immediately upon notice of significant damage (TRCA, 2018).

Testing Indicators Framework - Green Roofs

Component	Indicators	Construction Inspection	Assumption Inspection	Routine Operation Inspection	Verification Inspection
Testing Indicators
	Soil characterization testing	x	x		(x)
	Green roof irrigation system testing	x	x	x
	Green roof leak detection testing		x		x
Note: (x) denotes indicators to be used for Performance Verification inspections only (i.e., not for Maintenance Verification inspections)

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.

Any form of rain or snow.

Toronto and Region Conservation Authority

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

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.

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

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.

Abiotic transfer of water vapour to the atmosphere.

Watercourses and Lake Ontario, to which Stormwater and Combined Sewer Overflows discharge.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

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

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.

Water ponded on the ground surface.

(1) The wearing away of the land surface by moving water, wind, ice or other geological agents, including such processes as gravitation creep; (2) Detachment and movement of soil or rock fragments by water, wind, ice or gravity (i.e. Accelerated, geological, gully, natural, rill, sheet, splash, or impact, etc).

An underground water storage reservoir into which stormwater is directed and allowed to percolate into the underlying native subsoil.

An excavated area lined with geotextile filter cloth and filled with clean granular stone or other void forming material, that receives runoff and allow it to infiltrate into the native soil; can also be referred to as infiltration galleries, French drains, dry wells or soakaway pits.

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.