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TP Section 11: Vegetated (Green) Roof Systems

TP-11.1 General

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A vegetated roof design (green roof) is defined as a roof membrane system with a top layer of living plants in an engineered soil blend (growth medium). System components include a membrane protection layer, drainage layer, filter layer and a root barrier between the soil and roof membrane. Green roof systems are also referred to as vegetated roof covers, roof gardens, eco-roofs, or landscaped roofs. Vegetated roofs of varying slopes include both conventional and protected membrane designs. (See Figure 1)

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Vegetated roofs are categorized based on type of installation:
  • Substrate System

    Growing medium is conveyed onto a combination of components required for containment, drainage, and protection from root penetration. The vegetation is planted onsite.

  • Modular System:

    Self-contained trays of growing medium and plants grown offsite and placed onto the roof surface. A membrane protection layer is installed between the roof membrane and trays.

  • Pre-Grown Vegetated Blanket System:

    Thin mats or rolls of vegetation grown offsite and placed over a combination of components required for containment, drainage, and protection from root penetration. Additional thickness of growing medium may also be installed in accordance with project requirements.

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Warranty coverage of this section applies to commercial buildings for leak repairs on extensive vegetated roof systems with soil depths of 200mm (8") or less for five (5) or ten (10) year terms only. The cost to remove and replace the vegetated roof components to facilitate access to the roof membrane for investigation and repair of workmanship related leaks is included however; it is the responsibility of the building owner to cover costs for removal and replacement of items that were not installed by the roofing contractor.
Revised

2012-09

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Only ARCA Warranty Ltd. approved membranes that are specifically accepted by the membrane manufacturer for use in vegetated roof systems qualify for a Warranty Certificate.

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The completed roof membrane system shall be tested for water tightness prior to and following the installation of green roof components and membrane protection layer (See item 11.8 Leak Detection System). Insulation and vegetated roof system components above the roof membrane are not to be installed until all identified deficiencies are repaired and the membrane system has been re-tested to validate the roof system is water tight and dry.

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Roof leaks as the result of membrane damage due to the work of others, maintenance or from root penetration are not covered under the Warranty Certificate.

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Roof mounted structures or equipment exceeding 91 kg (200 lbs.) in mass or when roof point loads exceed 5 kPa (105 PSF), shall be supported on curbs, sleepers, support pads, or pedestals attached to the structure or decking. Structural supports shall be designed by a structural engineer, shall conform to the Alberta Building Code and to the satisfaction of the authority having jurisdiction.
Revised

2018-10

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A licensed design professional (i.e. structural engineer) must provide written confirmation to the owner the structure and deck will support a fully saturated green roof system for dead loads and environmental live loads in accordance with local building codes.

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The care or maintenance of the vegetation and growth media including water and/or wind erosion, or the survival or health of the plants is not covered under the ARCA Warranty Certificate.

TP-11.2 Drainage

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The drainage slope shall be a minimum 1:50 (1/4"/ft.).

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The maximum roof slope is restricted to 6:12.

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For roof slopes greater than 2:12, suppliers of the proprietary vegetated roof system or the design professional shall determine materials and components necessary to prevent slippage or sheering of the overburden on steep slope applications. ARCA Warranty Ltd. must provide written approval prior to the mechanical attachment of components through any part of the roof membrane system.

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Membrane level scuppers shall be provided at the roof perimeter as emergency drainage or in steep slope design may be the primary drainage. Scuppers must have gravel screens installed.

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Internal roof drains shall have a vegetation and soil free zone around the drain opening with a minimum dimension of 762mm (30") for inspection and maintenance purposes.

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Control flow drains are not recommended with a vegetated roof system.

TP-11.3 Penetrations, Curbs, and Roof Perimeter

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Except for roof drain and pedestal fall protection roof anchors, all roof penetrations shall be contained within or supported by a curb secured to the structure or decking.

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Vegetation and soil free zones adjacent to parapets, curbs, and walls require a non-combustible protective roof covering which remains in place through the entire service life of the roof system.

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Roof parapets, wall surfaces, curbs for roof penetrations and mechanical units, expansion joints, equipment supports and pedestal fall protection anchors shall extend a minimum distance of 200mm (8") above the surface of the growth medium, gravel ballast, or concrete pavers.

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Vegetation and soil free zones are required a minimum of one meter wide along the roof perimeter, roof/wall junctions, fire separation walls, around mechanical unit curbs, and roof access hatches or doors.

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Roof area dividers or building expansion joints, and curbs for roof openings (i.e. skylights, plumbing vents, chimneys, etc.) require a minimum vegetation and soil free zone width of 300mm (12"). The vegetation free zone may be exempt for support curbs or sleepers for posts or columns that do not penetrate the roof deck. The membrane flashing on the vertical face shall be protected with corrosion resistant sheet metal base flashing beginning 25mm (1") from the top surface of the roof membrane in a conventional membrane system or from the top of the XPS insulation layer in a protected membrane system. (See Figure 2)

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Placements of non-combustible roof coverings such as concrete pavers, loose gravel, or metal walkway systems must be elevated from the membrane or insulation surface with a protection mat/drainage board for gravel, or pedestal system for pavers or walkways and must facilitate drainage.

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Curbs or physical barriers for separation between vegetated and non-vegetated zones shall be made of materials unaffected by moisture, fertilizers or leachate from growing medium and must facilitate drainage. L-shaped sheet metal up-stands shall be suitably supported opposite the growing medium to prevent leaning. Separation barriers must not be attached through or penetrate the roof membrane. Joints of up-stand sections are to be fastened to prevent displacement or opening of joints. Curb height shall extend a minimum of 50mm (2") above the surface of compacted growing medium.

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Roof penetrations for cable, conduit, gas lines, or irrigation lines shall be located in the vegetation free zone. Install a curb or enclosure with a watertight sloped top where the lines run through the vertical face a minimum of 200mm (8") above the ballast or paver. Gum boxes or pitch pans are not permitted under any circumstance.

TP-11.4 Roof Membrane System

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Membranes that provide waterproofing must be fully adhered to an approved insulation cover board or fully adhered directly to the supporting roof deck. Loose laid, mechanically fastened, or semi-adhered membranes are not permitted.

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The roof membrane system below the vegetated roof cover shall meet or exceed the designed wind uplift resistance for the building type and location (See link to Wind-RCI Calculator on ARCA website). The roof membrane manufacturer shall confirm system application requirements to meet design wind loads for the building location.

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For conventional roof design: Insulation must be attached to the supporting roof deck and/or vapour retarder membrane either by mechanically fastened, cold adhesive or hot asphalt and in accordance with ARCA Roofing Application Standards. Mechanical fastening is not permitted directly below the roof membrane except where membrane fastening is required at the roof perimeter and within the soil and vegetation free zone.

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For protected membrane roof design (inverted roofs): Only type 4, extruded polystyrene (XPS) insulation is approved and shall be loose laid over the waterproofing membrane in accordance with ARCA Roofing Application Standards.The dry weight of the vegetated roof cover (i.e. growth medium) shall meet the designed ballast weight for wind uplift resistance of the insulation.
  1. PVC membranes should not be in direct contact with XPS insulation; therefore requires a protection layer between the insulation and membrane.

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All welded seams in the field of the roof require a minimum 150mm (6") wide continuous cover strip of membrane centered and heat welded on both sides in accordance with manufacturer’s written instructions.

TP-11.5 Roof System Dividers

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Roof sections with conventional roof membrane systems that include vegetated areas shall be divided into smaller sections by way of subsurface roof dividers to limit the spread of water in the roof system assembly should a leak occur.

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For convential roof designs:
  1. Subsurface roof dividers are required only below the vegetated roof area when the roof section has less than 50% of vegetated roof cover. A continuous subsurface roof divider shall segregate the perimeter of the vegetated area including the non-combustible roof cover from the rest of the roof section.
  2. Roof sections with vegetated roof cover of 50% or more requires subsurface roof dividers within the entire roof section including non-vegetated zones.
  3. The roof sections, which include vegetated and non-vegetated zones, shall be divided into sections no larger than 93 m² (10 squares). The dividers shall be evenly distributed with a maximum dimension of 15.2 metres (50 ft.) and a minimum dimension of 6.1 metres (20 ft.). The location of subsurface dividers must be shown on an as-built roof plan drawing which will be included with the warranty documents.
  4. Above surface roof dividers or building expansion joints installed with conventional or protected membrane systems shall be constructed in accordance with current standards in the ARCA Roofing Application Standards manual.
  5. Subsurface roof dividers are installed with a minimum 40 mil thick self-adhesive membrane adhered onto the vapour retarder membrane, continuously applied along the leading edge of insulation, and lapped a minimum of 150mm (6") to the top surface of the primary insulation. (See Figure 3)
  6. If the insulation cover board is ribbon or spot adhered, apply a continuous 19.0mm (3/4") wide bead of compatible sealant along the top surface of the membrane divider prior to installing the insulation cover board.

TP-11.6 Membrane Flashing

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The vertical extension of the membrane flashing on walls and curbs shall be fully adhered to an approved substrate and shall terminate a minimum distance of 200mm (8”) above the surface of the gravel ballast or concrete paver.

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Minimum height of membrane flashing at a door sill or door jamb shall be 100mm (4”) above the surface of gravel ballast or concrete paver.

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Membrane flashings for curbs and parapets shall be in accordance with ARCA application standards except where membrane upgrades are required for specific systems.

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Continuous cover strips of membrane a minimum width of 150mm (6") shall be centered and heat welded on both sides over all lap terminations (vertical and horizontal) in accordance with manufacturer’s written instructions.

TP-11.7 Roof Membrane Protection

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The completed and tested roof membrane system shall be protected from construction traffic and tools used to install and maintain a vegetated cover. Protection of the finished roof membrane must be in place during the installation and maintenance of the green roof system and remain in place as a permanent component of the assembly. Protection system components shall be pre-approved by the membrane manufacturer and ARCA Warranty Ltd. prior to installation. (See Figure 1)

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For protected membrane design (inverted roof): the roof membrane protection shall be Type 4, Extruded Polystyrene insulation (XPS) loose-laid over the primary membrane. The insulation provides thermal resistance for the roofing system as well as membrane protection from foot traffic and tools used for green roof installation and maintenance.
  • PVC membranes should not be in direct contact with XPS insulation therefore requires a separate protection layer between the insulation and membrane.

.3

For conventional membrane design: the roof membrane protection may be a combination of a root barrier membrane and drainage mat with suitable compressive strength to resist or recover from expected traffic and material loads. Any damaged drainage mat or boards must be replaced prior to the application of overburden.

.4

Roof sections with vegetated roof cover area of less than 50% requires membrane protection and a non-combustible roof cover a minimum of one meter wide adjacent to the separation curb or barrier.

TP-11.8 Leak Detection System

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Flood tests are not considered conclusive of system integrity therefore is not an acceptable substitute for a leak detection system.

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Accepted non-destructive electronic leak detection (ELD) of the roof membrane shall be a vector mapping (VM) system. A qualified technician shall conduct the leak detection test and provide to the roofing contractor a detailed report with a roof plan showing locations of all detected breaches or sign-off as being watertight.

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Initial ELD testing of the roof area shall be performed only when the roof membrane system is fully complete including all penetrations. The conductor wire required for leak detection testing shall frame only the area with vegetated roof cover including a minimum of one metre outside the vegetated roof separation barrier or up-stand.

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A conductive medium steel mesh, directly below the vegetated roof area, shall be installed by the roofing contractor under the fully adhered roofing membrane or insulation cover board. The application of the mesh shall be in conformance with the VM suppliers written instructions and compatible with the membrane application.

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A qualified technician from the supplier of the VM system is responsible for the installation of the conductor wire and related hardware on the roof membrane surface and to perform the subsequent ELD testing.

.6

The required number of leak detection tests under the roofing contractors’ scope of work is as follows:
  1. Prior to the installation of insulation and/or vegetated roof system components above the completed roofing membrane.
  2. After repair of breaches in the membrane system identified and recorded by the ELD technician if caused by the roofing contractor’s work. If the identified damage is caused by others, the cost of repair and subsequent leak detection testing is the responsibility of others.
  3. Following completion of the roofer’s scope of work. If breaches are detected, another test shall be conducted following repairs.

 

A leak detection test may be conducted following substantial completion of the project. All costs for the ELD test including the repair of any breaches in the roofing membrane will be the responsibility of others.

TP-11.9 Thermoplastic Membrane Systems for Vegetated Roof Systems

TP-11.9.1 PVC Membranes

  1. Carlisle - Conventional Membrane Design

    • 80 mil Sure-Flex PVC
  2. Sika Sarnafil - Conventional or Protected Membrane Design

    • 80 mil G476-15 PVC membrane

TP-11.9.2 TPO Membranes

  1. Carlisle - Conventional Membrane Design

    • 72 mil Sure-Weld Extra TPO
  2. Carlisle - Protected Membrane Design

    • 115 mil Sure-Weld, 105 AFX fleece back or 135 AFX TPO

      (Carlisle AFX membranes hot mopped over two ply mopped base sheet over concrete deck.)

  3. Firestone - Conventional Membrane Design

    • 80 mil Platinum TPO, TPO XR 110 / XR 115

TP-11.10 Vegetated Roof Assembly Above the Roof Membrane System

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This section provides general information and recommendations for applications or performance factors of the vegetated roof materials and products installed above the roof membrane or the insulation. The designer, roofing contractor, and roofing inspector shall familiarize themselves with the specified vegetated roof system to understand assembly requirements and component functions.

.2

The supplier of a proprietary vegetated roof assembly shall have a representative on site providing technical support during the initial start-up, and periodically through-out the installation of their products. A written report by the suppliers’ representative accepting the work of the roofing contractor at the completion of their scope of work shall be provided to the roofing contractor, the building owner or their agent, the roofing inspector, and ARCA.

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The roofing contractors’ scope of work is defined in the Trade Definitions established for Roofing and Related Sheet Metal and Vegetated Roof Systems which are available on ARCA’s website. Essentially the roofing contractor shall be responsible for the installation of the protective vegetated roof system layers and related components which cover the roof membrane. Irrigation components, aesthetic or decorative features on or adjacent to the growing medium may be the responsibility of others under separate contract.

.4

Decorative pathways, patio’s or podium deck surfaces accessible to people are to be installed over a membrane protection layer. The designer must take into consideration the compressive strength of the underlying materials to prevent damage to the insulation and roofing membrane from spot loads which may exceed design limits.

.5

It is recommended that sheet metal components in contact with moisture laden materials such as the filter layer and growing medium shall be fabricated from minimum 24 gauge stainless steel or 0.032” aluminum. Confirm with the supplier of growing medium or chemical fertilizer for alkalinity as this may affect the corrosion resistance of aluminum.

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Recognized Proprietary Vegetated Roof Systems
  • Carlisle Roof Garden System
  • Firestone SkyScape Roof System
  • LiveRoof
  • Siplastgreen
  • Soprema Sopranature System
  • XeroFlor
  • Zinco

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System Considerations
  • Drainage

    Vegetated roof drainage design must maintain optimum growing conditions in the growth medium which includes managing heavy rainfall without sustaining damage due to erosion or ponding of water on the surface. Lightweight composite drainage mats, boards, or trays below the growing medium allow for unimpeded, free-flow of moisture to the roofs drainage locations. A water retention layer between the drainage layer and growth medium may be incorporated to help maintain hydration of the growth medium during drought periods as well as improve storm water holding capacity to meet site conditions or regional regulations. Roof drains should be equipped with inspection chambers with removable lids and placed on top of the drainage layer so as to not impede flow of water on the membrane surface to the drain opening.

  • Plants and growing medium

    The engineered growth medium must be carefully designed to provide for excellent plant growth, and proper water holding capacity. Growing medium composition for extensive systems should contain low organic content whereby a minimum of 80% by volume contains inorganic material to improve fire resistant properties. Composition and thickness of growth medium is an important factor in plant selection. Selection of the vegetation can also provide fire resistance. Plants should be selected based on the buildings location and orientation where wind, sun, shading, snow and rainfall accumulations, as well as horticultural zones have a direct effect on the plants ability to survive.

  • Protection of underlying waterproofing systems

    Vegetated roof assemblies must protect the underlying waterproofing system from human activities (including the impact of maintenance) and biological attack. A root barrier must be included above bituminous membranes to prevent root penetration through the membrane or laps. Thermoplastic membranes (PVC, TPO) are generally root resistant and may not require a separate layer for root protection. Proper protection of the roofing membrane surface under and surrounding the vegetated roof system must be in place during installation and maintenance of a vegetated roof using materials that will not break down from exposure to fertilizers, moisture, or sunlight.

  • Waterproofing and insulation systems

    Waterproofing and insulation are critical components of the vegetated roof. Membrane system applications must be upgraded to a degree of redundancy that increases leak-free reliability. Including a non-destructive electronic leak detection (ELD) system helps to pinpoint breaches in the waterproofing membrane system without having to disturb the overburden to do the testing. The extent of overburden removal is determined in the general vicinity of the detected breach.

    Vegetated roof components and growing medium should not be relied upon for effective or consistent thermal resistance (heat gain, heat loss). Insulation thermal resistant (R-value) requirements for the building should be integral to the roof membrane assembly below the vegetated roof components. Drainage or protection layers must provide air circulation and vapour diffusion when placed onto Extruded Polystyrene insulation (XPS) in protected membrane designs (roofing membrane adhered to structural deck).

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Benefits

The potential benefits associated with vegetated roofs include:

  • Controlling storm water runoff
  • Improving water quality
  • Mitigating urban heat-island effects
  • Prolonging the service life of roofing materials
  • Reducing sound reflection and transmission
  • Creating wildlife habitat, and
  • Improving the aesthetic environment in both work and home settings.

As a result vegetated roofs may be appropriate as an addition to many types of buildings, including commercial, industrial, institutional, and residential settings. On the other hand, the additional cost, possible water usage to irrigate the plants, and required ongoing maintenance may make them less appropriate.

TP-11.11 Referenced Guidelines and Standards for Vegetative Roof Systems

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Green Roofs For Healthy Cities - Training Manuals
  • Green Roof Design - 101
  • Green Roof Infrastructure: Design and Implementation - 201
  • Green Roof Waterproofing and Drainage - 301
  • Green Roof Plants and Growing Medium - 401

Link to GREEN ROOFS FOR HEALTHY CITIES for more information on research, guidelines, products, and project information.

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North American Standards
  • ANSI/SPRI RP-14

    Wind Design Standard for Vegetative Roofing Systems

    This standard provides a method of designing wind uplift resistance of vegetative roofing systems. It is intended to provide a minimum design and installation reference for those individuals who design, specify, and install vegetative roofing systems. It shall be used in conjunction with, or enhanced by, the installation specifications and requirements of the manufacturer of the specific products used in the Vegetative Roofing System.

  • ANSI/SPRI VF-1

    External Fire Design Standard for Vegetative Roofs

    This design standard provides a method for designing external fire resistance for vegetative roofing systems. It is intended to provide a minimum design and installation reference for those individuals who design, specify, and install vegetative roofing systems. It shall be used in conjunction with the installation specifications and requirements of the manufacturer of the specific products used in the Vegetative Roofing System.

  • ANSI/GRHC/SPRI VR-1 2011

    Procedure for Investigating Resistance to Root Penetration on Vegetative Roofs.

    This standard is intended for testing the ability of roofing material to resist normal root and rhizome penetration.

  • FM Global

    Property Loss Prevention Data Sheets 1-35 Green Roof Systems

    This data sheet provides general guidelines for green roof systems. The green roof systems addressed in this data sheet are typified by a top layer of living plant material and soil (growth media or engineered soil) supported on the roofing assembly below.

  • ASTM Standards Associated with Green Roof Systems

    Subcommittee E06.71 Sustainable Building Standards
    • E2397-05 Standard Practice for Determination of Dead Loads and Live Loads.
    • E2396-05 Standard Test Method for Saturated Water Permeability of Granular Drainage Media
    • E2398-05 Standard Test Method for Water Capture and Media Retention of Geo-composite Drain Layers
    • E2399-05 Standard Test Method for Maximum Media Density for Dead Load Analysis
    • E2400-06 Standard Guide for Selection, Installation, and Maintenance of Plants