The “Dirt” on Green Roofs : a detailed look at green roofs

1. The “Dirt” on Green Roofs:a detailed look at green roofs Jamie McKay, P.Eng. Associate, Project Engineer, Leed A.P. M O R R I S O N H E R S H F I E L D www.morrisonhershfield.com Ottawa Toronto Calgary Edmonton Vancouver Atlanta Seattle Fort Lauderdale

2. Overview • Benefits of Green Roofs • Design Considerations • General Considerations • Proprietary vs. Custom • Green Roof System overview Review of Each component • Details • LEED Implications • Construction Considerations • Quality Assurance • Leak Detection • Maintenance & Operations Considerations

3. Green Roof Benefits Social Benefits • Storm-water retention and water filtering • Reduced heat island effects • Habitat and biodiversity improvements • Air cleansing and carbon sink Owner’s Benefits • Roof membrane protection & life extension (reduce temperature fluctuations and physical damage) • Sound insulation • Occupant benefits (therapeutic and added useable space). • Increased property value Naturescaping, City of North Vancouver

4. Design Considerations General Design Considerations • Consultant Roles & IDP (Architect, Structural, Envelope, Landscape, Mechanical, etc.) • New Construction vs. Existing Building (Structural limitations) • Building Height, Exposure and Surrounding Buildings (Sun, Wind, Shading, fire) • Accessible or non-accessible (Safety) • Intended use (water collection and filtering, urban garden, habitat protection/promotion, sitting/walking areas, etc.) • Plant Selection (soil depth, irrigation, maintenance, component affects) • Budget (initial and operating) • Proprietary systems vs. Custom Built

5. Design Considerations vs. Custom Built Pros: • Reduced system cost • Increased plant selection and customizing Cons: • Warranty • Weight increase • Plant replacement/Maintenance increase • Coordination issues • Increased Design fees Proprietary System Pros: • Technical support • Faster installation • Warranty • Less plant replacement &lower maintenance • Lighter weight Cons: • Higher capital cost • Limited options $ $

6. Design Considerations Examples of Proprietary Systems • Sopranature (Soprema) • Garden Roof (Hydrotech) • Sky Garden (Green Roof Tops) • Greengrid • Elevated Landscape Technologies • Xero Flor (vegetated blanket) • ZinCo (Mat and blanket)

7. Design Considerations System Overview • Vegetation • Growing medium • Water storage/absorption/drainage • Root Barrier • Insulation (if required) • Roofing membrane • Structural support Photo courtesy of: http://www.uwm.edu/Dept/GLWI/ecoli/Greenroof/benefits.html

8. Design Considerations Vegetation & Growing Medium The Green Roof’s intended function will typically dictate the vegetation selection. There are two main categories: Extensive • Thin growing material • Little or no irrigation (except set-up) • Low plant diversity • Light weight • Low maintenance • Typically not accessible to public • Lower capital cost Intensive • Deep soil • Irrigation typically required • High plant diversity • Heavy weight • Accessible to public • Higher capital cost Photos courtesy of BuildSmart

9. Design Considerations Water Drainage & Storage • Allow free drainage of water under growing medium and above roofing membrane • Provide storage space for excess water, which reduces need for irrigation • Allow aeration of soil, which reduces cultivation needs and maintenance costs Photos courtesy of Greenrooftops.com

10. Design Considerations Root Barrier An often overlooked, but critical component of a green roof assembly. A poor root barrier can substantially shorten the life of the roof. The selection is typically based on: • Plant selection • Soil depth or use of gravel or voiding material • Proprietary vs. custom built assemblies • Chemical or non-chemical treatment • Sensitivity of underlying structure • Membrane selection (monolithic vs. sheet) Photos courtesy of Greenrooftops.com Photos courtesy of zinco.ca

11. Design Considerations Insulation Insulation placement is dictated mostly by design requirements and philosophy. There are two main categories: Conventional Roof Insulation placement under roofing membrane, which requires: -A separate air and vapour barrier -Air barrier tie-in with walls -Recovery board -Maintenance paths Inverted Roof Insulation installed over roofing membrane, which requires: -Ballast to withstand insulation uplift -Two level drains -Higher vents, parapets and upturns Photos courtesy of NRC, Institute for Research in Construction Photos courtesy of soprema

12. Design Considerations Roofing Membranes The roofing membrane needs to be carefully selected based on durability and lifespan. Once covered it will not be easily serviced. Design Considerations: • Structure (wood, steel, concrete) • Membrane durability (thickness & adhesion) • Weather & installation conditions (wet, cold, dusty) • Visible at parapet walls (UV stabilized) • Compatibility with adjacent materials • Maintenance, renewals, embodied energy, cradle to cradle/grave, regional materials, recycled content • Historical performance • Skilled workforce • Warranty requirements

13. Design Considerations Membrane types: • Multi-layer systems (SBS, BUR, Hot liquid, cold liquid). • Attachment methods: • Torch-applied • Mechanically fastened • Hot mopped • Cold mopped • Adhesive Pros: Durable (longer life/thicker systems) Cons: Higher cost, Fire/Insurance issues, slower install, aesthetics

14. Design Considerations Membrane types: • Single layer sheet systems (PVC, TPO, EPDM). • Attachment methods: • Mechanically fastened & welded • Adhesive & welded Pros: Less cost, Less insurance issues, architectural (exposed), faster install Cons: Less expected life, thinner systems

15. Design Considerations LEEDCanadaTM Credits Related to Green Roofs Sustainable Sites • Credit 5: Reduced Site Disturbances • Credit 6: Stormwater Management • Credit 7: Heat Island Effect Water Efficiency • Credit 1: Water Efficient Landscaping • Credit 2: Innovative Wastewater Technologies • Credit 3: Water Use Reduction Energy & Atmosphere • Credit 1: Optimize Energy Performance Material & Resources • Credit 3: Resource Reuse • Credit 4: Recycled Content • Credit 5: Regional Materials • Credit 6: Rapidly Renewable Materials • Credit 8: Durability Indoor Environmental Quality • Credit 7: Thermal Comfort Innovation and Design Process • Credit 1: Innovation in Design

16. Design Considerations Details Almost all leaks occur at transitions, penetrations – “The details” Designers need to consider: • Supplementary Drawing/Detail/Specification review (BEP, Manufacturer, roofing trade) • Integrated Design with Architectural, Structural, Mechanical, Plumbing, Electrical, and Landscape • Drawings for specific details: • Roof edge (parapets & transitions) • Penetrations (incl. mechanical) • Division walls • Accessible areas • Ponds Drawing courtesy of PWL, dockside Green, Victoria

17. Design Considerations Sloped Green Roofs • Typically less than 30º • Requires soil stabilizing structure • Orientation and shading consideration • Specific plants and root structure • Perimeter edge drainage • Access for maintenance Photos courtesy of Greenrooftops.com

18. Design Considerations Photos courtesy of soprema Roof Edge Details The roof perimeter specifics: • Be accessible for building maintenance, to control plant growth, and add fire breaks (where required) • Include concrete or similar perimeter curbs to enclose vegetation (should be moisture tolerant) • Include rock ballast or pavers (inverted roofs) • Include guard rails for accessible roofs Photos courtesy of Calhoun school, NY

19. Design Considerations Roof Penetrations Similar to roof perimeters, penetrations require separation from vegetation. Design Considerations include: • Two stage drains and extra high access collars • Roof anchors and safety lifeline paths. • Irrigation lines • Electrical conduit • Skylights & Access hatches • Railings, fixed curbs, benches, playground equipment Photos courtesy of www.miller-roofscapes.co.uk Drawing courtesy of PWL, dockside Green, Victoria

20. Construction Considerations Quality Assurance Methods • Mock-ups • Testing (adhesion, thickness, etc.) • Enhanced Field Review • Manufacturer representative’s field reports • Flood Tests • Leak Detection systems

21. Construction Considerations Leak Detection systems • Electric Field Vector Mapping • Infrared Scans • Electric tracing & monitoring systems

22. Maintenance & Operations Considerations A maintenance and renewals plan should be developed for the building to assist the Owners/Tenants with M/O requirements and future replacement. The following should be considered for maintaining and operating a green roof: Vegetation Plant selection (roots, watering (initial vs. continued), sun/shade sensitivity, weed tolerance, prevailing winds, etc.). What will happen to them when the roofing assembly requires replacement? Repairs? Available access (personnel, material removal and addition for repair/replacement, etc.). Knowledgeable maintenance staff or hired maintenance group Roof membrane Periodic review of membrane? How? Leak monitoring? EFVM? Drains are clean, and penetrations are clear Review for ponding Warranty requirements?

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