vegetative roof systems: waterproofing membranes and

Vegetative Roof Systems April 2009

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Vegetative Roof Systems: Waterproofing Membranes and

Construction Details By:

James R. Kirby, AIA Associate Executive Director, Technical Communications

NRCA

Feb 18 Baltimore Feb 26 Atlanta

March 5 Chicago March 11 Seattle April 23 Boston

Summary of topics

•  Definitions •  Types of vegetative roof systems •  Vegetative roof concepts •  Decks •  Membranes •  Systems •  Design considerations •  Construction details •  Slope •  Integrity testing


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Vegetative Roofs – Are they for real?

Definitions

•  A roof assembly consists of a roof deck, membrane or primary roof covering, and roof insulation designed to weatherproof and sometimes improve a building’s thermal resistance.

•  A waterproofing assembly consists of a structural substrate or deck; membrane; and protection, drainage and insulation course designed to waterproof a habitable space.

•  A vegetative roof assembly consists of a structural deck, waterproofing system (membrane and associated components) and overburden with plantings in a growth medium.

•  When we discuss systems, we don’t include the deck.


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Types of vegetative roof systems

Types of vegetative roof systems

•  NRCA defines 3 types of vegetative roof systems: –  Extensive (2”-6”)

–  Semi-intensive (6”-10”) –  Intensive (10”+)


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Extensive vegetative roof system

Extensive vegetative roof


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Semi-intensive vegetative roof system

Semi-intensive vegetative roof


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Intensive vegetative roof system

Intensive vegetative roof


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Vegetative roof concepts

Vegetative roofs

•  Vegetative roofs combine roofing concepts and waterproofing concepts. Vegetative roofs can be constantly wet, but require roof systems details modified to accommodate growth medium and “vegetative” components.


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Vegetative roofs

•  Use a waterproofing membrane; a vegetative roof likely is a wet environment.

•  NRCA recommends it be adhered with insulation above it; a vegetative membrane is protected.

Stay dry—no leaks


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Why adhered…?

•  NRCA recommends direct-to-deck adhered waterproofing system. A breach in the membrane may not allow moisture beneath the membrane.

•  NRCA recommends insulation be installed above the membrane.

•  NRCA recognizes loose-laid and partially adhered (e.g., gridded attachment), but has concerns about the potential for horizontal leak travel, which makes it more difficult to locate a leak source.

Growth medium…?

•  Built-in place vs. trays •  NRCA recommends growth medium

be built-in place.


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Decks


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Deck design considerations

•  Generally the responsibility of a structural engineer

•  Some of the considerations are: –  Live loads, such as snow, ice and rain –  Construction loads, such as moving installation

equipment, workers and materials

–  Dead loads, such as mechanical equipment –  Dead loads, such as the waterproofing system, growth

medium, and other overburden—concrete toppings, pavers, and water that is retained

–  Deck strength

Deck design considerations

•  Expected deflection (positive drainage) •  Drainage •  Expansion joint placement •  Structural support of curb and penetration

members and details (remember those large trees?)

•  Deck attachment to structure •  Deck suitability for membrane adhesion/

attachment •  Suitability for water tests


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A vegetative waterproofing membrane contractor can only inspect the surface of the deck;

and is not responsible for slope, structural integrity, and method of

deck attachment, for example.

Deck types

•  Concrete •  Steel •  Wood


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Concrete deck

•  Concrete substrates should be properly cured and the surface should be dry.

•  If a suitable surface cannot be obtained within a reasonable time period, postpone membrane installation. An adhesion test is recommended to determine appropriate membrane adhesion.

•  Concerns: –  Form-release agents, concrete-curing compounds must be

compatible –  Honeycombs, tie-wire holes and other voids should be patched –  Concrete fins should be removed to provide a smooth surface

•  Concrete decks must be sloped for drainage.

Concrete deck •  ASTM D5295, “Standard Guide for Preparation of

Concrete Surfaces for Adhered (Bonded) Membrane Waterproofing System,” which includes surface condition test D4263, “Test Method for Indicating Moisture in Concrete by the Plastic Sheet Method.” –  An 18- by 18-inch polyethylene sheet is taped to a

concrete surface. Someone observes if moisture collects on underside of polyethylene sheet. NRCA does not feel this is an appropriate test method.

•  NRCA does not recommend the use of D4263.


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Concrete deck

•  NRCA suggests performing an adhesion test by applying a small test patch (e.g., 36- by 36-inch test patch) of the waterproofing membrane, allowing it to cure and then attempting to peel the membrane from the concrete substrate to determine adhesion.

•  There is no standardized peel-test method, so this must be coordinated with the vegetative roof system contractor, manufacturer and owner. Alternately, the waterproofing manufacturer should provide an appropriate test method to determine dryness of the concrete deck or an appropriate test to determine adhesion.

Steel deck

•  Steel decks should be 18 gauge minimum and have moisture-resistant gypsum board or cementitious board fastened to their top surfaces to serve as the vegetative roof waterproofing membrane’s substrate.

•  Joints between overlay boards should be stripped in prior to application of the vegetative roof waterproofing membrane.

•  Overlay boards should be a minimum 5⁄8 inch thick. •  Fasteners used for attaching overlay boards must be

corrosion resistant or resin-coated screws and plates. •  Overlay boards also should improve the stiffness and

reduce deflection of the steel deck/overlay board composite.

•  Steel decks must be sloped for drainage.


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Wood deck

•  Wood decks should consist of heavy lumber (e.g., 3- to 4-inchthick planks) and have moisture-resistant gypsum board or cementitious board fastened to their top surfaces to serve as the vegetative roof waterproofing membrane’s substrate.

•  Overlay boards should be a minimum 5⁄8 inch thick.

•  Fasteners used for attaching overlay boards must be corrosion-resistant or resin-coated screws and plates.

Wood deck

•  Wood decks can also consist of marine-grade plywood. The surface must be smooth, and holes, open joints or gaps between boards or panels should be plugged or covered.

•  Joints between plywood boards should be stripped in prior to application of the membrane.

•  Marine-grade plywood decks must be sloped for drainage.

•  Plywood panel edges should bear on joists or blocking to reduce deflection from traffic. Thickness and deflection characteristics of wood substrates are important design considerations.

•  Wood decks should be sloped for drainage.


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Deck deflection

•  A critical issue of the substrate for the waterproofing is the amount of deflection that will occur during dead and live loading. Too much deflection can be detrimental to the service life of a waterproofing system.

•  NRCA recommends a structural engineer design the deck so that deflection of the deck is suitable to minimize the potential for ponding water.

Structural capacity of deck

•  Design based on saturated loads

–  Extensive: 12 psf minimum –  Semi-intensive: 40 psf minimum

–  Intensive: 60 psf minimum


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Deck surface

•  Clean, dry, smooth and acceptable for a vegetative roof system waterproofing membrane

Vegetative roof waterproofing membranes


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Vegetative roof waterproofing membranes

•  Hot-fluid-applied polymer-modified asphalt membrane

•  APP- and SBS-polymer-modified bitumen sheet membrane

•  EPDM membrane •  PVC membrane •  One- and two-component, fluid-applied

elastomeric membrane

Hot-fluid-applied polymer-modified asphalt membrane

•  215-mil-thick minimum •  Fabric-reinforced •  32 F temperature limit

•  ASTM D 6622, “Standard Guide for Application of Fully Adhered Hot-Applied Reinforced Waterproofing Systems”


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Hot-fluid-applied polymer-modified asphalt membrane

•  Installation –  Surface, crack and joint prep –  Primer

–  Reinforce corners, etc. with 6 inch reinforcement –  Continuous moppings to the required thickness

•  90 mil base coat, fabric, 125 mil top coat, protection board

APP- and SBS-polymer-modified bitumen sheet membrane

•  Two-layer minimum •  APP – heat-fused, adhesive •  SBS – heat-fused, hot asphalt, adhesive •  Heat fuse all seams •  40 F temperature limit •  ASTM D 6769, “Standard Guide for Application of Fully

Adhered, Cold-Applied, Prefabricated Reinforced Modified Bituminous Membrane Waterproofing Systems”


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APP- and SBS-polymer-modified bitumen sheet membrane


–  Reinforce corners, etc. with 6 inch reinforcement –  If using cold adhesive, allow appropriate “flash”

time

–  Heat-fused, hot asphalt, cold adhesive

EPDM membrane

•  60-mil-thick minimum, reinforced •  Adhered, not mechanically attached or

loose-laid •  40 F temperature limit •  ASTM D5834, “Standard Guide for

Application of Fully Adhered Vulcanized Rubber Sheets Used in Waterproofing”


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EPDM membrane

•  Installation – Surface, crack and joint prep – Allow membrane to relax for at least 30

minutes – Clean membrane prior to adhering – Adhesives – Stripping in seams is considered good

practice

PVC membrane

•  60-mil-thick minimum, reinforced •  Adhered, not mechanically attached or

loose-laid

•  40 F temperature limit •  No ASTM standards for PVC

waterproofing


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PVC membrane

•  Installation – Surface, crack and joint prep

– Allow membrane to relax for at least 30 minutes

– Clean membrane prior to adhering – Adhesives

One- and two-component, fluid-applied elastomeric membrane

•  Polyurethane elastomers, some modified with coal tar or asphalt

•  Fabric-reinforced

•  One vs. Two – mixing, heat/humidity, pot life •  40 F temperature limit •  No ASTM standards for elastomeric

membrane waterproofing


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One- and two-component, fluid-applied elastomeric membrane


–  Reinforce junction of horizontal and vertical surfaces –  Spray, roller, trowel, squeegee

–  Continuous coats to the required thickness •  60 mil wet thickness base coat, fabric, 60 mil wet thickness

top coat, protection board

System design considerations


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•  Slope the deck/substrate to provide positive drainage.

•  Concrete, steel and wood decks need to be structurally sound to provide an appropriate substrate.

•  Anticipate deflection to avoid ponding. •  Moisture-resistant insulation should be installed

above, not under, the membrane. Do not use insulation to provide positive drainage.

•  Membrane flashing details should terminate at or above the top surface of the growth medium.


•  UV and mechanical protection are needed for membrane flashings.

•  Raise expansion joints above membrane.

•  Install drains in all areas bounded by expansion joints, area dividers and/or perimeters.

•  Design details at perimeters and penetrations to allow access for maintenance of the waterproofing membrane.


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•  Safety/Access/Maintenance should be considered during design.

•  Anchorage points and safety rails

•  Foot paths and walkways •  Water source for plants •  Maintenance contract with waterproofing

contractor and/or landscaping contractor

A quick look again at the components


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•  Protection board is recommended for all vegetative roof systems.

•  Root barriers may or may not be necessary. –  Membrane specific –  May act as protection course

•  Drainage course is needed to promote the movement of water under insulation, etc, and above the membrane. –  Promotes positive drainage

•  Internally drained is suggested. •  Insulation should be installed above the membrane.

System components •  WP membrane •  Protection course •  Root barrier •  Drainage layer •  Insulation

•  Construction details—I am not going to discuss aeration layer, moisture-retention/reservoir layer, filter fabric/geotextile or growth medium


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Protection course over hot-fluid-applied wp membrane

photo credit: Jim Brosseau

Root barrier

•  Root barriers prevent penetration into the waterproofing membrane. – Chemical (e.g., copper) – Physical (e.g., 20-60 mil HDPE)

•  Germany’s FLL has established tests for root repellency. PVC and TPO roofs are a natural root barrier.


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Drainage

•  Provides the principal mechanism for discharging storm water when growing medium is fully saturated.

•  Air movement under the growth media helps dry insulation.

•  Porous mats, granular media, or rigid drainage, modular system with built in drainage. Some systems allow for some water retention for the plants.

•  Most are loose-laid. Come in sheets or rolls.

Drainage photo credit: Mark Gaulin


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Drainage

•  Internally drain vegetative roof systems. –  Edge drainage can be a difficult detail to ensure that

components and growth medium are contained for the expected service life of the vegetative roof system.

Draining edge: not recommended


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Insulation recommendations

•  NRCA recommends insulation be above the waterproofing membrane

•  Have high-density •  Have high compressive strength: 40 psi minimum •  Be moisture resistant

•  Effectively this means rigid XPS board (extruded).

•  Overall, the waterproofing system should be able to withstand a moist environment for prolonged periods of time.

XPS insulation photo credit: Jim Brosseau


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Construction detail design considerations

Construction detail design considerations

•  Slope and drainage

•  Expansion joints and control joints •  Curbs and penetrations (get figure about

spacing from 2008 intro to constr details)

•  Flashings •  Membrane base flashings •  Sheet-metal counterflashings and terminations


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Slope and drainage

•  NRCA recommends all green roof systems over habitable spaces be designed and built to provide positive drainage.

•  Min 1/8:12 (0.6 degrees) •  Localized areas—crickets, saddles •  Primary drains and overflows are typically

installed at the same level as the vegetative roof membrane’s surface.

Expansion joints and control joints

•  Same location as the building’s structural expansion joints

•  Designer is responsible for details that allow building movement and placement of expansion joints.

•  It is recommended a designer consider: –  Thermal movement characteristics of a building –  Structural supports and deck –  Vegetative roof waterproofing membrane –  Climatic conditions –  Proper detailing –  Drainage areas/path

•  The waterproofing system should slope away from expansion joints so water does not accumulate.


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Curbs and penetrations

•  Drains, piping, conduit, mechanical units, equipment supports, and other projections or penetrations

•  A maximum amount of space should be provided between pipes, walls and curbs. NRCA recommends –  a minimum 12 inches of clearance between pipes –  a minimum 12 inches of clearance between pipes and curbs or

walls –  a minimum 12 inches of clearance between curbs and curbs or

walls •  NRCA recommends penetrations through a vegetative

roof system not be located so they restrict the flow of water

•  Pipe clusters are not recommended because of the difficulty to properly flash them


•  Curbs, wood blocking, penetrations, drains and drain leaders should be firmly anchored and in place before installation.

•  All openings for penetrations should be cut through the deck and the void around the penetration filled with compatible material before installation.

•  Vibrations from surface-mounted mechanical equipment should be isolated.

•  The installation of drainage piping is encouraged to direct equipment discharge water directly to drains.


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•  Heavy loads, such as large mechanical units, should not be wheeled or rolled over a completed vegetative roof waterproofing membrane because they may cause damage to it.

•  Protection boards should be installed if work is required over a completed vegetative roof waterproofing membrane before installation of the system components and overburden. After the work is completed, the temporary protection should be removed and any damage repaired and water tested.

Flashings

•  The most vulnerable part of a vegetative roof system for water entry is the intersection of horizontal and vertical surfaces, such as parapet walls and penetrations.

•  Flashings and membranes are subject to differential horizontal-to-vertical movement and can separate from their substrate, tear and become a source for water entry.

•  NRCA recommends flashing details accommodate movement at horizontal-to-vertical conditions at walls and decks.


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Flashings

•  There are two types of flashings for vegetative roof systems: –  membrane base flashings

–  sheet-metal counterflashings

Membrane base flashings

•  NRCA recommends the height of a base flashing be a minimum of 8 inches above the surface of the membrane and 4 inches above the surface of the growth medium.

•  Membrane base flashings should be adhered to the substrate.

•  Some require fastening by termination bars or other appropriate mechanical fastening devices. Membrane base flashings also should be properly sealed along the top edge.


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Sheet-metal counterflashings and terminations

•  Sheet-metal counterflashings, or some other means of protecting the membrane flashing from UV exposure and physical damage, should be installed.

•  Some vegetative roof systems do not require protection from UV exposure; however, all base flashings should be protected from physical damage.


•  Sheet-metal counterflashings should be installed into or on the wall above the base flashing. NRCA suggests the design of counterflashings consist of separate reglet and counterflashing pieces, allowing installation of the sheet-metal counterflashing after the membrane base flashing is complete. Projects where single-piece counterflashings have been installed will require removal and replacement of the metal flashing during future maintenance and rewaterproofing operations.


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•  Cast-in raggles or reglets is not recommended when precast walls are used—alignment concerns.

•  Counterflashings at vertical panel-to-panel joints are difficult to waterproof.

•  It is advisable to isolate metal flashings from the vegetative roof waterproofing membrane and base flashing when possible.


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Construction details

Construction details •  8 typical details

–  Wall flashing –  Roof Drain –  Low Parapet –  Continuous pipe penetration –  Plumbing vent –  Skylight, scuttle and smoke vent –  Expansion joint with metal cover –  Door threshold

–  Other •  Joint details at concrete deck •  Joint detail at cementitious board


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Wall flashing - PVC


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Semi-intensive vegetative roof system—note aggregate at drain

and perimeter/parapet


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Low parapet

Aggregate or pavers


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Area dividers, paver edge


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Slope considerations


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Slope for vegetative roof design

•  Typically, slopes can be up to 2:12 or 3:12 without special detailing

•  For steeper slope: – Generally only possible for extensive roofs – May need battens/restraints for loose-laid

elements – Soil erosion measures needed

Steep-slope vegetative roof


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Steep-slope vegetative roof

Steep-slope extensive vegetative roof system


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Steep-slope extensive vegetative roof system

Integrity testing


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NRCA recommends contractors verify the integrity of the waterproofing membrane

installation before proceeding with subsequent construction activities.

Methods to determine integrity

•  Flood test •  Flowing water test •  Electronic field vector mapping


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Flood test

•  A flood test—standing water test—is conducted by plugging drains and building dams to retain water on the surface of the vegetative roof waterproofing membrane with 2 inches of water for a minimum of 24 hours.

Flowing water test

•  Continuously flowing water over a vegetative roof waterproofing membrane—without closing drains or erecting dams—for a minimum of 24 hours.


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Electronic field vector mapping •  A low-voltage test which uses water as a

conductive medium •  An electrical potential is created between a

nonconductive membrane and a conductive deck or previously installed wire loop configuration

•  A technician locates membrane defects by finding vectors (ground fault connections) created by breaches in the electric field. An electric field is created by applying water on the membrane’s surface

•  Basically you “electrify” the membrane surface—when water goes through a defect, it “faults.” Technicians find the faults.

Summary of topics

•  Definitions •  Types of vegetative roof systems •  Vegetative roof concepts •  Decks •  Membranes •  Systems •  Design considerations •  Construction details •  Slope •  Integrity testing


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Questions?

James R. Kirby, AIA Associate Executive Director, Technical Communications

National Roofing Contractors Association

10255 W. Higgins Rd, Suite 600 Rosemont, IL 60018

800-323-9545

847-299-9070 x7570

[email protected]

www.nrca.net

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