Green Roofs: Engineer’s Perspective

NG Live!: Diane Cook & Len Jenshel: Gardens by Night

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Up on the RoofA lofty idea is blossoming in cities around the world, where acres of potential green space lie overhead.

Green Roofs: Engineer’s Perspective

Early Example

Green Roofs: Engineer’s Perspective

Recent Example

Green Roofs: Engineer’s Perspective

Fit For PurposeDurablePracticalSafe

Green Roofs: Engineer’s Perspective

Fit For PurposeWhy Green ?

Green Roofs: Engineer’s Perspective

Fit For PurposeWhy Green ?How Green ?

Green Roofs: Engineer’s Perspective

Fit For PurposeWhy Green ?How Green ?Who Knows ?

Green Roofs: Engineer’s Perspective

DurableStrengthStability

Green Roofs: Engineer’s Perspective

DurableStrengthStabilityBuilding Envelope

Green Roofs: Engineer’s Perspective

DurableStrengthStabilityBuilding EnvelopePerformance

Green Roofs: Engineer’s Perspective

DurableStrength & Stability

Building EnvelopePerformanceReparable

Green Roofs: Engineer’s Perspective

PracticalAccessible

Green Roofs: Engineer’s Perspective

PracticalAccessibleUsable

Green Roofs: Engineer’s Perspective

PracticalAccessibleUsableFeasible

Green Roofs: Engineer’s Perspective

PracticalAccessibleUsableFeasibleOptimal

Green Roofs: Engineer’s Perspective

SafeFall Prevention

Green Roofs: Engineer’s Perspective

SafeFall PreventionSecure

Green Roofs: Engineer’s Perspective

SafeFall PreventionSecureWind-proof

Green Roofs: Engineer’s Perspective

SafeFall PreventionSecureWind-proofFire-proof

Green Roofs: Engineer’s Perspective

Fit For PurposeDurablePracticalSafe

Engage. Innovate. Inspire.

Slowing Down On Green Roofs

Peak Flow Attenuation and Volume Reduction

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Slowing Down On Green Roofs Peak Flow Attenuation

Source: www.ec.gc. ca

Or With Green Roof

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Slowing Down On Green Roofs Volume Reduction

Source: environmentalsciencesociety. org

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Slowing Down OnBlue Roof

Source: www.perviouspavement. org

Source: Alumasc

Roof D

ischargeD

ownstream

Storm

Sew

er or

Com

bined Sew

er

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Slowing Down OnBlue Roof

Source: www.perviouspavement. org

DETENTION AND EVAPORATION OFFERED BY BLUE ROOFS

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Slowing Down On Green Roofs Green Roof: Types

Intensive : > 8”, $$$$$

Extensive: 2” – 8”, $$, 17 – 50 lbs/sfBuilt-up or Tray Systems

Source: www.wbdg. org

Source: www.salinitymanagement. org

INTENSIVE SEMI-INTENSIVE EXTENSIVE

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Slowing Down On Green Roofs Green Roof: detention, evaporation, infiltration, percolation, evapotranspiration, . . . Water designed to flow through medium vertically before laterally along drainage layer.

Source: www.greenroofplan. com Source: environmentalsciencesociety. org

VEGETATION

GROWING MEDIUM

FILTER / ROOT BARRIER

DRAINAGE

INSULATION

WATER-PROOFING

STRUCTURE

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Slowing Down On Green Roofs Green Roof: detention, evaporation, infiltration, percolation, evapotranspiration, . . . Water designed to flow through medium vertically before laterally along drainage layer.

Special design considerations needed when designing a pitched green roof to preserve hydrological benefits of green roof.

Source: environmentalsciencesociety. orgSource: www.hydrotechusa. com

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Slowing Down On Green Roofs Green Roof: detention, evaporation, infiltration, percolation, evapotranspiration. . .

Source: www.princeton. edu

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Slowing Down On Green Roofs Green Roof: detention, evaporation, infiltration, percolation, evapotranspiration, retention

Source: Paul MJ & Meyer JL, and USEPA

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Slowing Down On Green Roofs Green Roof: detention, evaporation, infiltration, percolation, evapotranspiration, retention

Source:environmentalsciencesociety. org

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Slowing Down On Green Roofs

Source:Hydrological performance of extensive green roofs in New York City: observations and multi-year modeling ofthree full-scale systems. T B Carson et al 2013 Environ. Res. Lett. 8 024036 doi:10.1088/1748-9326/8/2/024036

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Slowing Down On Green Roofs

Source: enr.construction. com

Green Roof: detention, evaporation, infiltration, percolation, evapotranspiration, retention

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Slowing Down On Green Roofs Green Roof: detention, evaporation, infiltration, percolation, evapotranspiration, retention

Source: enr.construction. com

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Slowing Down On Green Roofs

Source: prairieecosystems.pbworks. com

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Slowing Down On Green Roofs Green Roofs: with cisterns or harvesting

Source: www.ce.t.kyoto-u.ac. jp

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Slowing Down On Green Roofs

Source: nusdeltares. org

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Slowing Down On Green Roofs Green Roof: Effects of Rain Duration & Intensities

Source: uregina. ca (modified)

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Slowing Down On Green Roofs Green Roof: Runoff Quality & Pollution Control

Source: www.lid-stormwater. net

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Slowing Down On Green Roofs Hydrological Selection of Green Roof Components:

Drainage

• Low Transmissivity Drainage Fiber Mat

• Drainage Layer

• Use of Lightweight Aggregate?

• Plastic Drainage Sheets ?

• Closed-cell polystyrene trays ?

• Maintain Aerated Conditions in the Growing Medium

• Ability to Remove Excess Stormwater without Causing Erosion

• Slope to Drain

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Slowing Down On Green Roofs Hydrological Selection of Green Roof Components:

Growing Medium

• Sponge-like Water Holding Capacity• Inorganic Content & Material• Organic Content & Material• Saturated Weight of Growing Medium• Medium Thickness

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Slowing Down On Green Roofs Hydrological Selection of Green Roof Components:

Selecting Plants

• Drought, wind and ice tolerant

• Prairie species

• Avoid large drifts of single species

• Water absorption

• Requires very little or no irrigation

• Requires very little or no fertilizer

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Slowing Down On Green Roofs Impact of Green Roofs on Urban Catchment

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Slowing Down On Green Roofs

Williams Engineering Canada Inc.

Inquiries:Williams Engineering CanadaBUILDEX Calgary, November 6, 2013

Wilma Leung C.Eng., MICE,LEED-AP Email: wleung@williamsengineering.com

THANK YOU