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

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)

Construction Inspection Tasks

Construction inspections take place during several points in the construction sequence, specific to the type of LID BMP, but at a minimum should be done weekly and include the following:

1. During site preparation, prior to BMP installation to ensure the roof structure is ready for green roof construction work and confirm that BMP layout area matches approved design drawings and that construction materials meet design specifications
2. After installation of leak detection system (if applicable) to ensure it was done properly
3. At installation of water-proofing membrane, prior to installation of root barrier, drainage layer and overflow outlets to ensure it was done properly and to confirm that slopes are acceptable
4. After installation of root barrier, drainage layer (including filter fabric/layer) and overflow outlets, prior to installation of growing medium and plants to ensure it was done properly and confirm that depth and slopes are acceptable
5. After installation of growing medium layer and plants to ensure it was done properly and to confirm depth, slopes and elevations at overflow outlets are acceptable; After installation of irrigation system to confirm system is functioning
6. Prior to hand-off points in the construction sequence when the contractor responsible for the work changes (i.e., hand-offs between the building and green roof installation contractors)
7. After every large storm event (e.g., 15 mm rainfall depth or greater) to ensure roof drainage or flow diversion devices are functioning and adequately maintained. You can also download and print the table here
   

A Vacuum Truck used for permeable pavement maintenance, which sucks up excess sediment and fines trapped between the pores of block pavers. Conducting this maintenance regularly helps maintain the practice's optimal infiltration rate during large rain events. (Source: STEP).

Permeable Pavements: Green Roofs

Construction Sequence Step & Timing	Inspection Item	Observations*
Site Preparation - after site clearing and grading, prior to BMP excavation and grading	Natural heritage system and tree protection areas remain fenced off
	ESCs protecting BMP layout area are installed properly
	CDA is stabilized or runoff is diverted around BMP layout area
	BMP layout area has been cleared and is staked/delineated
	Benchmark elevation(s) are established nearby
	Construction materials have been confirmed to meet design specifications
BMP Excavation and Grading - prior to backfilling and installation of pipes/catchbasins	Excavated soil is stockpiled outside the CDA
	Excavation location, footprint, depth and slope are acceptable
BMP Installation – after installation of pipes/catchbasins, prior to completion of backfilling	Structural components (e.g., pavement base, curbs) installation is acceptable
	Impermeable liner installed correctly, if applicable
	Installations of sub-drain pipes (e.g., locations, elevations, slopes), standpipes/monitoring wells are acceptable
	Sub-drain trench dams installed correctly (location, elevation)
	Surface coarse installation (elevation, slope, monitoring wells) is acceptable

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).

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

Soil particles with a diameter less than 0.050 mm.

The rate at which stormwater percolates into the subsoil measured in inches per hour.

Sustainable Technologies Evaluation Program

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.