Nrca Roof Manual

The NRCA Green Roof Systems Manual

2007 Edition

The NRCA Green Roof Systems Manual2007 Edition

Published by the National Roofing Contractors Association10255 W. Higgins Road, Suite 600, Rosemont, IL 60018-5607

2007 by the National Roofing Contractors AssociationAll rights reservedPublished 2007Printed in the United States of America

No part of this publication may be reproduced or distributed in any form or by any means or stored in a database or retrieval systemwithout prior written permission of the publisher.

National Roofing Contractors Association10255 W. Higgins Road, Suite 600Rosemont, IL 60018-5607(847) 299-9070Fax: (847) 299-1183Web site: www.nrca.netE-mail: [email protected]

The NRCA Green Roof Systems Manual2007 Edition 3

Important Legal Notice for Users ofThe NRCA Green Roof Systems Manual2007 Edition

Purpose of the Manual

The NRCA Green Roof Systems Manual2007 Edition (Manual) is published by the National Roofing Contractors Association (NRCA) foreducational and informational purposes only. NRCA is not undertaking to render specific professional advice. Readers must rely solely ontheir own judgment or consult a technically competent roofing professional to determine what procedure, whether included in the Manualor not, is appropriate for their purpose. NRCA does not approve or endorse any specific products, methods, practices or sources ofinformation. The Manual should not be referenced in any way that implies such approval or endorsement.

Disclaimers

The information and data contained in the Manual have been obtained from sources believed to be reliable. However, the various codes,regulations, standards and practices referenced in the Manual are subject to change, and the Manual is current only as of its originalpublication date. Make sure to consult appropriate sources for the most up-to-date versions of all codes, regulations and standards.Further, it should not be assumed that (i) all acceptable or applicable sources of information, procedures and techniques are containedin the Manual, or (ii) additional measures may not be required under certain circumstances or conditions.

NRCA makes no guarantee, representation or warranty, express or implied, at law or in equity, and NRCA expressly disclaims any and allsuch guarantees, representations or warranties whatsoever as to the validity, accuracy or sufficiency of the information set forth in theManual and assumes no responsibility or liability in connection therewith. Although NRCA recommends the use of the Manual by privateindustry and others, it is intended to be voluntary and nonbinding, and NRCA assumes no liability or responsibility in connection with theuse or misuse of the Manual or information included therein, or in connection with any modifications to or adaptations of the Manual by auser, purchaser or other party, and expressly disclaims any such liability or responsibility.

By using the information contained in the Manual, the user expressly assumes all risk of loss, harm or injury resulting from the useor misuse of such information. Additionally, the information presented in the Manual is complex, may not be appropriate in allinstances, and requires verification and use by technically competent roofing professionals. Modification to all or parts of the informa-tion included in the Manual by the user may affect the results, accuracy, reliability or other aspects of the information.

By using the Manual, the user acknowledges and accepts the foregoing limitation of liability and disclaimers, and agrees that NRCA isnot responsible for injuries, claims, losses or damages to the user or third parties arising directly or indirectly out of the users use ofthe Manual and/or the information contained therein.

Amendments

NRCA may, from time to time, amend and/or update the Manual. Such updates and amendments may create significant differencesamong successive editions of the Manual. The Manual is current only as of the original publication date indicated thereon.

Copyright

NRCA owns all copyrights in the Manual. The contents of the Manual may not, in whole or in part, be reproduced, copied or disseminat-ed, entered into or stored in a computer database or retrieval system, or otherwise used without the prior written consent of NRCAexcept that users may reproduce a limited number of pages, figures or construction details solely for purposes of responding to pro-posals, preparing shop drawings and similar noncommercial, limited uses.

This page is intentionally left blank.

The NRCA Green Roof Systems Manual2007 Edition is writtento provide technical information concerning the design andinstallation of quality green roof systems.

The information contained in this manual represents the con-sensus of knowledgeable, practicing waterproofing and greenroof system contractors throughout the U.S. In developing andpublishing this manual, the National Roofing ContractorsAssociation (NRCA) is presenting time-tested and proven best-practice guidelines that are applicable throughout the U.S. forroofing and waterproofing buildings and other structures. Theseguidelines may be more conservative than practices employedby some designers, manufacturers and installers. NRCA recog-nizes some designs and applications may vary according to cli-matic conditions and some geographical areas may employ areapractices that are sound and time-proven. NRCA does not meanto imply by any statement or exclusion in this manual that suchpractices are unsatisfactory or inappropriate.

The science and art of roofing and waterproofing buildingsand other structures continue to experience change spurredlargely by technological innovations and new product develop-ments. Ongoing and new research is also expanding the indus-trys knowledge of roof and waterproofing systems and theirdesign and installation. NRCA is committed to maintaining TheNRCA Green Roof Systems Manual2007 Edition as an up-to-date, authoritative technical reference concerning the design andinstallation of quality roof and waterproofing systems. Futureupdated editions of this manual are planned as new significantinformation about roof and waterproofing systems and theirdesign and installation becomes available.

Users of this manual who are seeking clarification of its guide-lines or wish to submit recommendations for revisions or addi-tions to future editions of this manual should contact:

Technical Services SectionNational Roofing Contractors Association10255 W. Higgins Road, Suite 600Rosemont, IL 60018(847) 299-9070Fax: (847) 299-1183E-mail: [email protected]

Acknowledgments

NRCA gratefully acknowledges its task force and committee mem-bers who contributed their time, effort and expertise in the develop-ment of this manual.

NRCAs Waterproofing Task Force was primarily responsiblefor researching and analyzing topics and developing the text,figures and construction details contained in this manual. Themembers of this task force at the time the manual was devel-oped and published were:

Frank E. Lawson Jr., task force chairmanThe Lawson Roofing Co. Inc.San Francisco

Charles BechtelHarold J. Becker Co. Inc.Dayton, Ohio

Thomas R. DessentDessent Roofing Co.Chicago

Don GuthrieWaynes Roofing Inc.Sumner, Wash.

Robert W. Therrien Jr.The Melanson Co. Inc.Keene, N.H.

James R. Kirby, AIA, NRCA staff liaisonNational Roofing Contractors AssociationRosemont, Ill.

Also, members of NRCAs Manual Update Committee,Technical Operations Committee and Executive Committee pro-vided review comments for the manual and input and guidanceto the Waterproofing Task Force.

In addition, NRCA acknowledges the efforts and expertise ofits staff involved in the development and publication of the man-ual, including staff from its Technical Services Section and theediting and print production staff of the Communications andMembership Development Section.

Foreword


General Green Roof Project Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Green Roof System Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23

Green Roof System Construction Details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .119


Contents


General Green Roof Project Considerations


Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .132. Notes to Owners and Designers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13

2.1 Proper Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .132.2 Quality Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .142.3 Quality Workmanship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

3. Pre-bid Conference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

4. Pre-job Conference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

5. Material Storage and Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

6. Temporary Green Roof Waterproofing System . . . . . . . . . . . . . . . . . . . . . . . . .15

7. Weather Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157.1 Cold Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167.2 Hot Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167.3 Wind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167.4 Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

8. Deck and Structural Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . .16

9. Surface Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

10. Slope and Drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

11. Expansion Joints and Control Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

12. Curbs and Penetrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

13. Flashings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1813.1 Membrane Base Flashings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1813.2 Sheet-metal Counterflashings and Terminations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

14. Quality Assurance and Water Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19

15. Overburden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

16. Post-water-test Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

17. Warranties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

18. Building Owner Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

19. Pre-job Conference Checklist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21

1. Introduction

The General Green Roof Project Considerations section of thismanual has been written to provide an overview of general infor-mation concerning the design and installation of quality greenroof systems. The information contained in this document isintended to complement The NRCA Roofing Manual series andshould be used as a guideline to prepare proper specifications.Consult The NRCA Roofing Manual: Membrane Roof Systems2007 and The NRCA Roofing and Waterproofing Manual, FifthEdition for more data and specification information.

This information represents the consensus of professionalgreen roof system contractors throughout the U.S. A green roofsystem contractor is a professional waterproofing or roof systemcontractor familiar with the installation of green roof systems. Agreen roof system is a roof area of plantings/landscapinginstalled above a waterproofed substrate. Some design criteriaand application techniques may vary according to climatic condi-tions, and each geographical area may employ specific areapractices that are sound and time-proven for that area. NRCAdoes not intend to imply by any statement or exclusion thatproven area practices are unsatisfactory.

The NRCA Green Roof Systems Manual2007 Edition definesgreen roof system, green roof assembly and waterproofing asfollows:

Green roof system: a roof area of plantings/landscaping installedabove a waterproofed substrate at any building level that is sep-arated from the ground beneath it by a man-made structure. Agreen roof system consists of a waterproofing system and itsassociated componentssuch as protection course, root barri-er, drainage layer, thermal insulation and aeration layerand anoverburden of growth medium and plantings.

Green roof assembly: a substrate and a green roof system.

Waterproofing: treatment of a surface or structure to preventthe passage of water under hydrostatic conditions.

Green roof system technology and building construction con-tinues to evolve. New, ongoing research is expanding the indus-trys knowledge of green roof assemblies and their design andinstallation. Readers are encouraged to contact NRCA or NRCAmembers in their geographical area for specific advice concern-ing area practices and current technical information.

NRCA recommends a green roof system be designed only after anumber of criteria have been carefully considered, including:

Climate and geographical location

A buildings intended use and design life expectancy

Exterior and interior temperature, humidity and use conditions

Code requirements

LEED considerations

Type and condition of substrate

Structural system

Slope and drainage

Green roof waterproofing membrane

Green roof system type (e.g., intensive [deep]), includingoverburden

Accessibility and building configuration

Building movement

Type and amount of insulation, protection and drainage needed

Need for ventilation during installation

Compatibility with adjacent building and/or systemcomponents

Construction sequencing

Worker safety

Potential building additions

Odors generated by certain system application methods

Snow loads, water-retention loads

Construction traffic

Penetrations

Landscape maintenance

These criteria play important roles in the ultimate success orfailure of a green roof assembly and should be considered by adesigner to determine the appropriate components of a greenroof assembly, applicable products and specifications, and con-struction details to be used.

In addition, a designer should be certain green roof materialmanufacturers requirements are taken into account, as well asrequirements of applicable insurance, building code enforcementand/or other regulatory agencies. It is recommended designerscommunicate with the manufacturer and consult material manu-facturers specifications during the design of a green roofassembly.

2. Notes to Owners and Designers

Achieving a green roof system that will perform its functionssatisfactorily for an anticipated service life requires properdesign, quality materials and quality workmanship.

2.1 Proper Design

Knowledgeable selection of compatible building materials, quali-ty green roof system materials and systems that will withstandthe conditions of the area where a building is located is vital to aquality green roof assembly design. Properly prepared specifica-tions with accurate drawings and details are essential. Specificrequirements regarding a new green roof assemblys compo-nents and installation should be carefully detailed by a designer.

A designer is responsible for proper specifications and draw-ings. Green roof system contractors and material manufacturersshould be consulted for input during the design phase.


2.2 Quality Materials

Material selection should be based on the time-proven quality ofa green roof assembly and its compatibility and appropriatenessto the substrate rather than solely on economic considerationsor length and scope of a warranty.

2.3 Quality Workmanship

NRCA suggests designers work with qualified professional greenroof system contractors and consult them during the designphase and before specifications or contract documents are pre-pared. The work should be performed by skilled, trained workersfamiliar with the specified product.

3. Pre-bid Conference

For green roof system projects for which drawings and specifi-cations have been prepared and two or more green roof systemcontractors are asked to submit sealed bids to perform specifiedwork, NRCA recommends a pre-bid conference be conducted. Apre-bid conference can serve the following purposes:

Introduce all the parties involved in the project, such as theowners representative, designer, landscape contractor andcontractors key personnel

Provide a forum for a thorough review of the project docu-ments and requirements and the owners special needs

Establish the conditions under which temporary waterproofingand/or traffic paths will be used and who will pay for them

Provide an opportunity to identify and resolve any questions,discrepancies, contradictions or errors in written specificationsand drawings

Provide an opportunity to discuss best practices, as well aslimitations for job-site setup, work hours, staging, storingmaterials, and removal of materials and debris

Identify and resolve any misconceptions in the scope of work

Identify the quality-control and inspection process

Before scheduling a pre-bid conference, a designer or buildingowners representative should prepare an agenda for the meetingand distribute it to all invited parties. If the identity of interestedbidders cannot be determined before the pre-bid conference, suchas in public bid projects, the agenda should be posted and madeavailable to potential attendees before the conference. A pre-bidconference should be attended by all responsible parties, includingthe owners representative, the designer, estimators and key per-sonnel of the bidding contractors and any subcontractors. The pre-bid meeting should be scheduled to allow adequate time for bidpreparation between the pre-bid meeting and the date on whichsealed bids are to be submitted. Ideally, the project documents,including the drawings and specifications, should be distributed toall the bidders before the date of the pre-bid conference to alloweach bidder the opportunity to review the documents. A writtenrecord or meeting minutes of the conference should be maintainedby a designer along with any changes (addenda) to the contract

documents and distributed to all parties in a timely manner follow-ing the meeting and well in advance of the bid deadline.

In summary, a pre-bid conference, if conducted properly, canresult in more accurate bidding and fewer change orders duringconstruction, as well as a more thorough understanding of theproject.

4. Pre-job Conference

Once a project has been awarded, NRCA recommends a pre-jobconference be held for green roof system projects. This confer-ence should be attended by the owner, architect/engineer ordesigner, general contractor, site contractor, green roof systemcontractor, consultant, inspector or quality-assurance supervisor,deck contractor, landscaping contractor, mechanical contractor,electrical contractor and any others whose work may interfacewith or affect the waterproofing project. The conference shouldbe scheduled well in advance of any deck completion and beforeordering materials and beginning work. If a manufacturers guar-antee or warranty is specified, representatives from the water-proofing material manufacturer(s) should be present. A writtenrecord should be made of the proceedings from this meetingand should become a part of the job record. If a green roof sys-tem contractor or waterproofing materials manufacturer discov-ers problems during inspection of a deck, a second preinstalla-tion inspection attended by the affected parties should be held toverify corrective measures have been taken.

A designers specifications, plans, and all green roof systemand flashing details should be reviewed at the pre-job conference.Any discrepancies between the designers contract documentsand manufacturers specifications should be discussed andresolved. In the event that certain discrepancies arise, the manu-facturers representative should be consulted to assist in resolv-ing the issue. Any known building code or architectural directivesthat conflict with these requirements should be resolved.

NRCA recommends the directives listed below be followed toensure a successful pre-job conference:

Review approved submittals for the green roof system.

Establish trade-related job schedules and appropriate tradecoordination and sequencing, including appropriate curingtimes; the schedule should provide for timely installation ofany penetrations, attachments, equipment, overburden and/orprotection to avoid or limit traffic on the green roof water-proofing membrane.

Establish construction schedules and work methods that willprevent damage to the green roof system. These may includeprovisions for installation of a temporary green roof water-proofing system or temporary green roof waterproofing sur-face protection devices, such as plywood. Installation of trafficpaths or walkways helps protect a finished green roof water-proofing membrane and system from foot traffic and mecha-nized construction equipment.

Establish guidelines for inspection and repair of the deck,including identifying the parties who are responsible forinspection and repair.

14 The NRCA Green Roof Systems Manual2007 Edition


Coordinate all appropriate walls, curbs, drains and other pene-trations before installation of the green roof system.

Establish those areas on the job site that will be designated foraccess, staging, work, storage and disposal areas.

Establish suitable weather conditions and working temperaturecriteria to which all parties should agree.

Establish provisions for on-site surveillance after green roofwaterproofing membrane application is completed to ensurethe finished green roof waterproofing membrane is not dam-aged by other trades, and if damage does occur, properrepairs are performed in a timely manner.

Establish safety regulations and safety requirements, includingconsiderations for safety of workers.

Establish quality-assurance requirements and procedures,including the level of authority to be granted to quality-assurance personnel to direct changes in the work.

Establish water-testing requirements and procedures, and des-ignate a party responsible for signing off after successfullywater testing the completed green roof waterproofing mem-brane and/or green roof system.

Establish a timeline for proper installation of overburden.

Establish the need for appropriate green roof waterproofingmembrane personnel to be on-site when overburden is placedon the green roof waterproofing membrane in case of damage.

Establish a quality-control and inspection process, and estab-lish who is responsible for it.

Establish a water source for irrigation.

At the conclusion of the pre-job conference, the party request-ing any proposed changes to the project conditions or greenroof system should:

Give written notice of the desired changes to all parties

Secure written agreement to the changes from the projectdesigner, owner and all other parties affected by the change

Additionally, the owner or designer should provide writtenmeeting minutes to all parties with action items noted. A pre-jobconference checklist is provided on page 21.

5. Material Storage and Handling

NRCA recommends the following for the storage and handling ofmaterials:

All green roof system materials that are susceptible to retain-ing moisture or may be damaged by moisture should bestored in a dry location and protected from freezing.

All green roof system materials that are susceptible to ultravio-let (UV) damage should be covered or stored in a location thatprotects them from UV damage.

When moisture-sensitive materials are stored outside, theyshould be placed on pallets or platforms that are raised offthe ground. Materials sensitive to moisture should be covered

with water-resistant coverings that have been properlysecured. Coverings that are breathable, such as water-resistant tarpaulins, are preferred.

Roll materials should be stored on end to prevent rolls frombecoming deformed or damaged. Single-ply sheet materialsmay be stored as shipped with rolls lying horizontally or asrecommended by the manufacturer. When storing green roofsystem materials on a deck surface, caution should be takennot to overload the deck or structural assembly.

Lids should be secured on cans of stored material.

Water-based materials should be protected from freezing.

Solvents, adhesives, foam components and sealants should bestored at proper temperatures.

Insulation materials should be stored and handled with care.When insulation is required to be dry at the point of installa-tion, it is imperative insulation materials be protected fromweather and moisture absorption. Some insulation materialsare extremely light and must be weighted in storage to preventwind damage, and some materials may need to be protectedfrom UV radiation.

6. Temporary Green Roof

Waterproofing System

Frequently, building construction sequencing leads to pressure forthe installation of green roof system materials during unsuitableweather conditions or ahead of the construction schedule. Thiscan be an issue for many types of green roof system projects butis most likely to be an issue for green roof system projects abovehabitable spaces or for those that can be used as work platformsor staging areas for other trades. As an effective means ofaddressing the problems caused by construction scheduling, atemporary waterproofing system installation may be necessary. Atemporary waterproofing system facilitates the application of thespecified green roof system during more suitable weather butallows other trades to complete their work before the permanentgreen roof system is installed. Thus, other trades may stay onschedule, completing their work under the protection of the tem-porary waterproofing system, and other trade traffic is limitedfrom potentially damaging the finished green roof system.

If a temporary waterproofing system is to be employed, NRCArecommends the specifications clearly state a temporary water-proofing system will be required; the type and specification oftemporary waterproofing system to be used; and whether thetemporary waterproofing system is to remain in place as part ofthe permanent waterproofing assembly. If it is to remain inplace, the temporary waterproofing system must be compatiblewith the permanent green roof system.

7. Weather Considerations

The performance of a green roof system depends on adhesion ofa membrane to a suitable substrate; consequently, weather con-ditions play an important factor in the successful installation of a


green roof system. A green roof system contractor is vitally con-cerned with the limitations imposed on construction activity bythe weather. To satisfy construction schedules and cope with thelimitations imposed by weather, a designer, general contractorand green roof system contractor should consider the followingguidelines for the application of green roof waterproofing mem-brane materials during various weather conditions.

7.1 Cold Temperatures

It is recommended that green roof system materials that havea cold-temperature sensitivity not be applied unless correctsolvent-, adhesive-, heat-welding- or bitumen-applicationtemperatures can be maintained.

For bituminous green roof system work, the heating andapplication of hot bitumen should conform to the manufacturersrecommendations. If proper application temperatures cannot bemaintained, green roof system application should cease. Hotbitumen must not be allowed to cool substantially before placingmembrane reinforcing in the bitumen. Depending on the cold-weather flexibility properties of certain modified bitumen materi-als, pre-warming and unrolling them in cold weather should beexecuted per manufacturers instructions. Moisture must not beallowed to condense or freeze or frost allowed to form on adhe-sives and solvents before bonding or welding takes place. Heatwelders must be maintained at proper temperatures to providecomplete, permanent welds. When installing heat-fused modifiedbitumen membranes in cold temperatures, equipment tempera-ture and application rate should be adjusted to achieve thoroughmembrane adhesion. Concrete decks can remain excessivelycold, which could have an adverse effect on the placement of themembrane and/or green roof system. Care must be taken tominimize material damage from the construction process duringcold weather. Additionally, solvents generally will require moretime to release from cold-applied adhesives; therefore, the cur-ing time will be longer.

7.2 Hot Temperatures

Hot temperatures and/or conditions of high humidity also pre-sent challenges to maintaining proper application conditions forbitumens, certain solvents, adhesives and membrane-weldingequipment. In hot weather, bitumen will cool more slowly, whichcan lead to sticking, making the membrane susceptible to physi-cal damage from the construction process, equipment and foottraffic. Hot weather combined with construction activity also canlead to damage of certain materials. Hot weather also cures orevaporates solvents and adhesives more quickly, which canimpair solvent welding, bonding and long-term adhesion.Humidity levels may also impair the welding, bonding and/oradhesion of various products. Heat welders must be properlyadjusted and monitored so as not to scorch, burn or overheatmaterials. Concrete decks can retain an excessive amount ofheat, which could have an adverse effect on the placement of themembrane and/or green roof system.

7.3 Wind

Wind can affect the application of green roof materials in manyways. Hot materials may be blown about, creating safety issues.Spray-applied liquid materials, such as adhesives and coatings,can become airborne in the wind and cause damage to surround-ing property or affect the quality of the applicationmasking oroverspray protection may be required. During even low winds,handling membrane sheet materials may become difficult anddangerous. Wind may affect proper application temperatures andcuring of materials. Insulation boards, sheathing and other rela-tively large, bulky materials may become difficult and hazardousto handle. Debris may become airborne and can contaminatelaps, seams and fluid-applied membranes, and the quality of thecompleted membrane may be compromised as a result.

7.4 Precipitation

Green roof system materials should not be installed if water,frost, snow or ice is present on an area under construction.Materials that can be adversely affected by these elementsinclude various deck materials, membranes, flashings, sealantsand coatings. NRCA recommends most materials for green roofsystems should not be installed if precipitation of any kind isoccurring or is imminent unless the area is adequately protected.After moisture has been present on the substrate, it is advisableto run an adhesion test to determine whether the membrane willproperly adhere to the substrate.

8. Deck and Structural Design

Considerations

Along with other factors, a successful green roof system appli-cation depends on a structurally sound deck. To ensure the con-struction of a structurally sound deck, provisions for the follow-ing items should be included in a buildings structural designand in the design of a deck:

Live loads, such as snow, ice and rain

Construction loads, such as moving installation equipment,workers and materials; some construction loads, such as rollerdollies used to transport single-ply materials, can exceed 600pounds in quite small areas

Dead loads, such as mechanical equipment, duct work, piping,and conduit such as fire sprinkler and electrical lines

Dead loads, such as a waterproofing system, soil overburden,concrete toppings, pavers and water that is retained

Deck strength (gauge, density, type and thickness)

Expected deflection

Drainage

Placement of expansion joints

Placement and structural support of curb and penetrationmembers and details

DRAIN AT LOCATION OF MAXIMUM CAMBER MAY NOT EFFECTIVELY DRAIN THE WATERPROOFING UNDER MINIMUM LOADING CONDITIONS

DRAINLOCATED HERE AIDSDRAINAGE

CAMBER

EXAMPLE SPAN OF 50'

LEVEL LINE

POINT OFDECK SUPPORT

POINT OFDECK SUPPORT

Figure 1: Example of deck camber where a drain located at midspan may not provide drainage


Attachment or securement provisions for a deck

Suitability for adhesion/attachment of a green roofwaterproofing membrane

Suitability for water test loads

A structurally sound deck should remain rigid so as not todeflect excessively under live loads. It should be understood thata green roof system contractor can only inspect the surface of adeck to receive the green roof waterproofing membrane materi-als and cannot assume responsibility for the decks slope, struc-tural integrity, method of attachment, or any other conditionsbeyond his or her control or professional expertise.

9. Surface Inspection

Before applying green roof waterproofing membrane materials, itis recommended that a green roof system contractor, with theappropriate parties, visually inspect the substrate surface to veri-fy it is clean, dry, smooth and acceptable for green roof water-proofing membrane and green roof system installation. A deckshould be brush- or broom-clean, reasonably smooth, free ofvoids or depressions, and adequately attached. This inspectionshould be attended by the green roof system contractor; materialmanufacturer; and all the appropriate parties, such as the gener-al contractor, deck contractor, architect/engineer or designer, andowners representative. All visible defects in the deck should benoted, and corrections should be made before beginning greenroof system work. It is recommended that the contractor who isresponsible for defects or damage to the deck be responsible forthe repairs. NRCA recommends project specifications clearlydefine this responsibility.

10. Slope and Drainage

NRCA recommends all green roof systems over habitable spacesbe designed and built to provide positive drainage. For greenroof systems over habitable spaces, NRCA recommends that adrainage layer be installed to facilitate the movement of water.

Because every green roof system project has its own set ofdrainage criteria, the designer is responsible for including properdrainage provisions in the green roof system design.

For green roof systems over habitable spaces, a designer

should specify a minimum 18:12 (0.6-degree) slope or greaterand should make provisions in the design for complete positivedrainage. To achieve the necessary slope throughout the entiresurface area, a designer should consider the following:

Structural framing for the deck

Deck type and its characteristics

Overburden material

Type of membrane specified

Penetration locations

Varying deck deflections

Building and deck layout

Flashing termination heights

Certain decks, such as precast concrete decks or long-spanprestressed concrete decks, may incorporate camber in anticipa-tion of future loading conditions. The camber must be consideredin the design of the slope and drainage system. Depending on thestructural design of a deck or slab system and placement ofdrains, the camber may assist or restrict drainage. See Figure 1.

This example illustrates that the computations for slopeshould be determined by the deflections expected in each partic-ular slab/deck.

NRCA recommends a designer consult the local building codeof jurisdiction regarding the required slope, primary drainageand secondary (overflow) drainage for each project. Buildingcodes dictate the number of drains, size of drain pipes andplumbing accessories, and the need for secondary drainage sys-tems. Design information for drainage is found in the plumbingsection of the applicable building code.

Primary drains and overflows are typically installed at thesame level as the green roof waterproofing membranes surface.For all green roof systems, it is recommended a protectioncourse be installed above the green roof waterproofing mem-brane and under any overburden. In some green roof systems,the root barrier may also act as a protection course. For greenroof systems, the drainage course is needed to promote themovement of water under insulation, reservoir layer, etc. See theconstruction details section of this manual for specific greenroof system details.


11. Expansion Joints and Control

Joints

Expansion joints and control joints are used to minimize theeffects of stresses and movements of a buildings componentsand prevent these stresses from splitting, buckling/ridging ordamaging a green roof system. Expansion joints in a green roofassembly should be placed in the same location as the buildingsstructural expansion joints. Each of a buildings components hasvarying coefficients of expansion, and each is subjected to vary-ing temperature changes and resultant thermal movement. It isthe designers responsibility to allow for building movement andplacement of expansion joints. In the design and placement ofgreen roof system expansion and control joints, it is recom-mended a designer consider:

Thermal movement characteristics of a building

Structural supports and deck


Climatic conditions

Proper detailing

Drainage areas/paths

Where expansion joints are used, the waterproofing systemshould slope away from expansion joints so water does notaccumulate at the base flashing of an expansion joint.

See the construction details section of this manual forspecific green roof system details.

12. Curbs and Penetrations

NRCA recommends curbs and penetrations be flashed into thegreen roof waterproofing membrane. The designer should prop-erly detail penetrations for drains, piping, conduit, mechanicalunits, equipment supports, and other projections or penetra-tions. See the Introduction to Details section of this manual foradditional information regarding penetrations and clearance.

A maximum amount of space should be provided betweenpipes, walls and curbs to facilitate proper installation of greenroof system materials. NRCA recommends a minimum 12 inchesof clearance between pipes, a minimum 12 inches of clearancebetween pipes and curbs or walls, and a minimum 12 inches ofclearance between curbs and curbs or walls. Green roof systemshave different installation methods that may require differentspacings, and certain project conditions may not allow theserecommended clearances; however, adequate space (i.e., clear-ance) is required for proper installation of the required flashingsat penetrations.

NRCA recommends penetrations through a green roof systemnot be located so they restrict the flow of water. Pipe clusters arenot recommended because of the difficulty to properly flashthem into a green roof waterproofing membrane.

All curbs, wood blocking, penetrations, drains and drain lead-ers should be firmly anchored and in place before installation of

a green roof waterproofing membrane and/or green roof system.All openings for penetrations should be cut through the deck andthe void around the penetration filled with compatible materialbefore installation of a green roof waterproofing membrane.

Vibrations from surface-mounted mechanical equipmentshould be isolated from a green roof waterproofing membraneand flashings. The installation of drainage piping is encouragedto direct equipment discharge water directly to drains.

Heavy loads, such as large mechanical units, should not bewheeled or rolled over a completed green roof waterproofingmembrane because they may cause damage to it. Protectionboards should be installed if work is required over a completedgreen roof waterproofing membrane before installation of thesystem components and overburden. After the work is complet-ed, the temporary protection should be removed and anydamage repaired and water tested.

See the construction details section of this manual forspecific green roof system details.

13. Flashings

The most vulnerable part of a green roof system for water entryis the point at which horizontal and vertical surfaces intersect,such as parapet walls and penetrations. Designers should care-fully design all flashing details.

Flashings and membranes are subject to differential horizon-tal-to-vertical movement and can separate from their substrate,tear and become a source for water entry into the green roofsystem and/or building interior. This can cause wrinkling andbuckling, delamination and loss of adhesion.

NRCA recommends designers develop flashing details thatcan accommodate movement at horizontal-to-vertical conditionsat walls and decks. This condition may occur where walls anddecks are not attached to each other or fixed-in-place.

There are two types of flashings for green roof systems:membrane base flashings and sheet-metal counterflashings.

13.1 Membrane Base Flashings

Membrane base flashings are generally composed of strips ofcompatible membrane materials used to flash horizontal-to-vertical junctions and/or transitions. NRCA recommends theheight of a base flashing be a minimum of 8 inches above thesurface of the membrane and 4 inches above the surface of thegrowth medium.

Membrane base flashings should be adhered to the substrateto prevent displacement and/or slippage. Depending on the typeof green roof system, termination of the system may vary. Somesystems require securing or fastening by termination bars orother appropriate mechanical fastening devices approved by themembrane manufacturer. Membrane base flashings also shouldbe properly sealed along the top edge. When phasing is required,other parties, such as the general contractor, should be responsi-ble for protection of the exposed green roof waterproofing mem-brane or leading edge before completion of the flashing system.


The installation of fillets at membrane base flashings toaccommodate horizontal-to-vertical plane change is consistentwith good green roof system practice when using bituminousgreen roof waterproofing membranes. Most thermoset and ther-moplastic green roof systems are capable of accommodating90-degree angle changes and do not require the use of fillets.

13.2 Sheet-metal Counterflashings and

Terminations

When green roof system base flashings are subject to UV expo-sure, sheet-metal counterflashings should be installed to cover thetop edge and overlap the exposed portion of membrane base flash-ings. In lieu of sheet-metal counterflashings, some other means ofprotecting the membrane flashing from UV exposure and physicaldamage is needed. However, some green roof systems do notrequire counterflashing to protect them from UV exposure.

Sheet-metal counterflashings should be installed into or onthe wall above the base flashing. NRCA suggests the design ofcounterflashings consist of separate reglet and counterflashingpieces, allowing installation of the sheet-metal counterflashingafter the membrane base flashing is complete. Projects wheresingle-piece counterflashings have been installed will requireremoval and replacement of the metal flashing during futuremaintenance and rewaterproofing operations.

Figure 2: Surface-mounted reglet with removable counterflashing

When precast walls are used, a designer should carefully con-sider the flashing provisions required to properly interface the

green roof system to the precast wall units. Cast-in raggles orreglets frequently used for this purpose are difficult to align.When they are not horizontally aligned, they hinder the properinstallation of sheet-metal reglets and counterflashing compo-nents. For this reason, the use of cast-in raggles or reglets is notrecommended. Also, where counterflashings span vertical panel-to-panel joints, the interfaces of counterflashings and panels withsealants are difficult to waterproof. In these situations, considera-tion should be given to camber, and the independent thermalmovement of the walls, green roof waterproofing membrane andflashings. Because metals have thermal expansion and contrac-tion characteristics that differ from most green roof waterproof-ing membranes, it is advisable to isolate metal flashings from thegreen roof waterproofing membrane and flashing when possible.

14. Quality Assurance and Water Tests

Continuous visual inspection during green roof waterproofingmembrane and green roof system application provides a com-plete and meaningful means of examining workmanship prac-tices. If part-time inspections are performed, the inspectionsshould occur at the beginning and end of significant phases andwhen another construction trades work may affect the perform-ance of the green roof system. The quality-assurance represen-tatives responsibilities should be clearly defined to ensure com-plete understanding of expectations of materials to be installed,installation methods and definition of deficiencies with appropri-ately defined corrective actions. The representative should, in atimely manner, provide the green roof system contractor withcopies of all reports prepared for the owner and should orallyinform the contractors field personnel of locations of itemsrequiring corrective action at the time of observation.

Quality assurance by the owner should continue after comple-tion of the green roof waterproofing membrane until all overbur-den work is completed.

NRCA strongly recommends horizontal green roof waterproof-ing membranes used as part of a green roof system be water-tested to prove their integrity prior to permitting subsequentconstruction. It is recommended the water test be witnessed andthe results confirmed in writing in case a problem arises afterjob completion.

Before installation of overburden, a water test is conducted toevaluate whether a green roof membrane is leak-free underhydrostatic (e.g., standing water) and/or nonhydrostatic condi-tions (e.g., flowing water). Prior to performing a water test, allappropriate parties and trades should be notified when the watertest will occur. A water test is conducted in one of two ways:

A standing-water test is conducted by temporarily plugging orotherwise closing any deck drains and erecting temporarydams where required to retain water on the surface of thegreen roof waterproofing membrane then flooding the surfaceto a maximum depth of 2 inches at the high point and retain-ing the water for a minimum of 24 hours or as required by themanufacturer. Installation and removal of any temporary damsshould not damage the membrane.

A flowing-water test is conducted by applying continuouslyflowing water over the green roof waterproofing membranessurface without closing drains or erecting dams for a mini-mum of 24 hours or as required by the manufacturer.

Selecting the correct water test depends on the structuralcapacity of the deck/substrate and the slope of the deck/greenroof system. However, job-site conditions may dictate themethodology of each projects water test. Decks without signifi-cant slope can be water-tested using a flood test or a flowing-water test. Decks with significant slope (e.g., a steep-slope greenroof system) can be water-tested using a flowing-water test.Determining the structural capacity of the deck is the responsi-bility of the designer.

Care must be taken so the weight of water retained does notexceed the load-carrying capacity of the structural deck and theheight of the water does not exceed the height of the lowestflashing. The water should be allowed to remain on the greenroof waterproofing membrane for a minimum of 24 hours for theflood test or for the flowing-water test or as required by the man-ufacturer, after which the areas beneath the membrane shouldbe inspected for leaks. If leaks are detected, the test should bestopped, repairs made to the membrane and the area retestedfor a minimum of 24 hours. The protection course should beinstalled over the tested area after successfully completing thewater test unless a protection course is an integral part of thegreen roof waterproofing membrane. The water test documentsthe performance of the green roof waterproofing membraneprior to placement of system components and overburden.

After the waterproofing test has been successfully completed,cover the membrane with a protection course, root barrier,moisture-resistant insulation and/or drainage course. Avoid allunnecessary traffic on the completed system prior to installationof the remaining components. If surfaces are exposed to the sunor if the green roof waterproofing membrane is being installedduring extremely hot weather, installation of the protectioncourse should occur within 24 hours.

This information and a sample water-test verification form arelocated in the Appendixes in the Green Roof System Guidelinessection of this manual.

Other methods, such as electric field vector mapping, areavailable to help determine the location of leaks, if they shouldoccur, either during a water test or after the green roof system iscompleted. This low-voltage test uses water as a conductivemedium and a wire-loop configuration to create an electricalpotential difference between a nonconductive membrane surfaceand a conductive structural deck or substrate, which is ground-ed. By applying water on the membrane surface, an electric fieldis created, and breaches in the membrane create vectors(ground fault connections). These vectors enable technicians tolocate green roof waterproofing membrane defects. This methodcan be configured to locate leaks within a green roof system.

15. Overburden

Consideration should be given to the selection of the overburdenand the components above a green roof waterproofing membrane.

A protection course, root barrier, drainage layer, moisture-resistantinsulation, aeration layer, moisture-retention layer, reservoirlayer and growth medium are installed on top of a green roofwaterproofing membrane. The selection of the overburden is asignificant part of an overall green roof system. The top of theoverburden should be 4 inches below the top of the flashingterminations. The components above a green roof waterproofingmembrane should all be compatible.

Accessory items, such as electrical conduits, irrigation lines,piping, etc., should not be attached to a green roof system.

16. Post-water-test Considerations

After a waterproofing system has been installed, the green roofsystem contractor and the general contractor should advise theappropriate parties of the need to provide surveillance and pro-tection of the green roof waterproofing membrane until the pro-tection course, system components and overburden are installed.Accessory items, such as electrical conduits, irrigation lines,piping, etc., should not be attached to a green roof waterproofingmembrane. Prolonged exposure of the green roof waterproofingmembrane to UV radiation also should be avoided to preventdamage. Damage to a green roof system caused by other tradesis a major source of subsequent green roof system problems.Construction traffic, staging, other trades work, debris and con-taminants should be kept off a finished green roof waterproofingmembrane. Damage can be difficult to discover, and leaks orpoints of water entry into the green roof system can remainundetected for an extended period of time, which can lead tofurther problems, such as structural deterioration. Where con-struction damage is anticipated, the use of a temporary water-proofing system should be considered before a project begins.

17. Warranties

The length of a waterproofing system warranty should not be aprimary criterion in the selection of a green roof waterproofingmembrane or green roof system because the warranty does notnecessarily provide assurance of satisfactory green roof systemperformance. The selection of a green roof system for a particu-lar project should be based on the products qualities and suit-ability for the prospective construction project. A long-term war-ranty may be of little value to a consumer if the green roof sys-tem does not perform satisfactorily and the owner is plagued byleaks. Conversely, if a green roof system is well-designed, well-constructed and well-manufactured, the expense of purchasing awarranty may not be necessary.

Warranty documents often contain restrictive provisions thatsignificantly limit the warrantors liability and consumers reme-dies in the event that problems develop. The warranty documentmay also contain other restrictions and limitations, such as apreclusion against assignment or transfer of the warranty, exclu-sion of damages resulting from a defective green roof systemand inclusion of monetary limitations. It is NRCAs position thatthe removal of growth medium, equipment, etc., that are notstrictly part of the green roof system is the responsibility ofothers. A green roof system contractor and green roof material


supplier are not responsible for removing any overburden of anykind installed by others over the green roof waterproofing mem-brane, including equipment, machinery, etc. It is recommendedthe respective manufacturers be consulted for warrantyclarification and responsibilities.

18. Building Owner Recommendations

Building owners should file all job records, drawings, specifica-tions and the water-test verification form for future reference.They should record maintenance procedures as they occur.

The following should be included in an owners maintenanceprogram:

Remove debris from the green roof system because debrismay be swept toward drains and may clog them. Check draininspection ports for soil and debris accumulation.

Notify the green roof system contractor immediately upon dis-covery of a green roof system leak.

Note conditions resulting in leakage.

Note whether the leak starts immediately after rain begins,stops shortly after rain stops or continues to leak until thegreen roof system is dry. All associated facts enable the diag-nosis and repair of green roof system problems to proceedmore rapidly.

Do not allow the installation of new penetrations through acompleted green roof system without consulting with thegreen roof system contractor and membrane manufacturer (ifthe green roof system is under a manufacturers warranty)about the methods and details for these installations.

Make the landscape maintenance workers aware they shouldnot damage exposed materials, especially the waterproofinglayer and flashings. Specific safety precautions may need to befollowed by trades working in a roof environment.

Make sure the installing green roof system contractor flashesand seals future penetrations when they are are added.

19. Pre-Job Conference Checklist

NRCA recommends the directives listed below be followed toensure a successful pre-job conference:

Review approved submittals for the green roof system.

Establish trade-related job schedules and appropriate tradecoordination and sequencing, including appropriate curingtimes; the schedule should provide for timely installation ofany penetrations, attachments, equipment, overburden and/orprotection to avoid or limit traffic on the green roof water-proofing membrane.

Establish construction schedules and work methods that willprevent damage to a green roof system. These may includeprovisions for installation of a temporary green roof water-proofing system or temporary green roof waterproofing surface protection devices, such as plywood. Installation of

traffic paths or walkways helps protect a finished green roofwaterproofing membrane and system from foot traffic andmechanized construction equipment.

Establish guidelines for inspection and repair of the deck,including identifying the parties who are responsible forinspection and repair.

Coordinate all appropriate walls, curbs, drains and other pen-etrations before installation of the green roof system.

Establish those areas on the job site that will be designatedas access, staging, work, storage and disposal areas.

Establish suitable weather conditions and working tempera-ture criteria to which all parties should agree.

Establish provisions for on-site surveillance after green roofwaterproofing membrane application is completed to ensurethe finished green roof waterproofing membrane is not dam-aged by other trades, and if damage does occur, properrepairs are performed in a timely manner.

Establish safety regulations and safety requirements, includ-ing considerations for safety of workers.

Establish quality-assurance requirements and procedures,including the level of authority to be granted to quality-assurance personnel to direct changes in the work.

Establish water-testing requirements and procedures, anddesignate a party responsible for signing off after successful-ly water testing the completed green roof waterproofingmembrane and/or green roof system.

Establish a timeline for proper installation of overburden.

Establish the need for appropriate green roof waterproofingmembrane personnel to be on-site when overburden isplaced on the green roof waterproofing membrane in case ofdamage.

Establish a quality-control and inspection process and who isresponsible for it.

Establish a water source for irrigation.

At the conclusion of the pre-job conference, the party request-ing any proposed changes to the project conditions or greenroof system should:

Give written notice of the desired changes to all parties

Secure written agreement to the changes from the projectdesigner, owner and all other parties affected by the change

Additionally, the owner or designer should provide writtenmeeting minutes to all parties with actions noted.



Green Roof System Guidelines

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

2. Green Roof Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .282.1 Extensive (Shallow) Green Roof Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .302.2 Semi-intensive (Moderate Depth) Green Roof Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .312.3 Intensive (Deep) Green Roof Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32

3. Green Roof System Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .333.1 Performance Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .333.2 Environmental Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .333.3 System Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

4. Decks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .334.1 Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .344.2 Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .344.3 Wood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .344.4 Deck Deflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34

5. Membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .345.1 Hot-fluid-applied Polymer-modified Asphalt Membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35

5.1.1 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .355.2 APP- and SBS-polymer-modified Bitumen Sheet Membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35

5.2.1 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .365.3 EPDM Membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

5.3.1 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .375.4 Polyvinyl Chloride (PVC) Membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37

5.4.1 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .385.5 One- and Two-component Fluid-applied Elastomeric Membranes . . . . . . . . . . . . . . . . . . . . . . . . . . .38

5.5.1 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .386. System Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39

6.1 Protection Course . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .406.2 Root Barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .406.3 Drainage Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .406.4 Moisture-resistant Insulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .406.5 Aeration Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .416.6 Moisture-retention Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .416.7 Reservoir Layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .416.8 Filter Fabric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .416.9 Engineered Soil-based Growth Medium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41

7. Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .427.1 Inspection Boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42



7.2 Irrigation and Electrical Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .427.3 Overburden Dividers and Terminations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .427.4 Drain Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .427.5 Metal Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .437.6 Area Dividers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

8. Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .438.1 System Assemblies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .438.2 Building Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .438.3 Quality Assurance and Water Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43

9. Low-slope vs. Steep-slope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4310. Care and Maintenance by Green Roof System Contractor . . . . . . . . . . . . . . . . .4311. Care and Maintenance by Landscaping Contractor . . . . . . . . . . . . . . . . . . . . . .4412. Reroofing Guidelines for Green Roof Systems . . . . . . . . . . . . . . . . . . . . . . . . .4413. Converting a Conventional Roof to a Green Roof System . . . . . . . . . . . . . . . . . .4414. Appendixes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44

14.1 Guidelines and Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4414.2 Water-test Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4514.3 Water-test Verification Form . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46


1. Introduction

The Green Roof System Guidelines section of this manual iswritten to provide in-depth technical information concerning thedesign and installation of quality green roof systems.

Green roof system practices vary considerably in differentparts of the U.S. because of the variety of conditions that existand the various materials that are available for use. Many times,green roof systems are essentially customized, meaning they aredesigned for specific substrates and structures and applied onjob sites. Adherence to the practices outlined in this manual isan option of each contracting firm. Area practices and the time-proven methods employed by individual firms are frequentlygiven priority over these recommended general procedures.

Green roof systems can be divided into three primary cate-gories: extensive (shallow), semi-intensive (moderate depth) andintensive (deep), which are defined as follows:

Extensive (shallow) green roof system: green roof system withan engineered soil-based growth medium approximately 2inches to 6 inches deep

Semi-intensive (moderate depth) green roof system: greenroof system with an engineered soil-based growth mediumapproximately 6 inches to 10 inches deep

Intensive (deep) green roof system: green roof system with anengineered soil-based growth medium greater than 10 inchesdeep

The green roof system details provided in this manual providedesign and installation information for:

Hot-fluid-applied polymer-modified asphalt membrane

APP- and SBS-polymer-modified bitumen sheet membrane

EPDM membrane

Polyvinyl chloride (PVC) membrane

One- and two-component fluid-applied elastomeric membrane

The information contained in this manual is intended primarilyto address new construction and replacement green roof systemsituations.

Because of the wide variety of green roof system products,this manual cannot address all the different methods and prac-tices for designing and installing all the products available todesigners, contractors and building owners.

In this manual, the National Roofing Contractors Association(NRCA) attempts to present the consensus of knowledgeable, prac-ticing green roof system and waterproofing contractors throughoutthe U.S. as to the practices and procedures for good roofing andwaterproofing. Where this manual provides specific suggestions orrecommendations, it should be noted these may be a more conser-vative approach than may be commonly provided by individualproduct manufacturers, green roof system designers or green roofsystem contractors. The green roof system design and applicationprocedures included in this manual are recognized to be sound andtime-proven and apply throughout the U.S.

The recommendations contained in the Green Roof SystemConstruction Details section of this manual should not be con-strued as the only methods for designing and installing greenroof systems. Some design criteria and application techniquesmay vary according to climatic conditions, and some geographi-cal areas employ area practices that are sound and time-proven. NRCA does not mean to imply by any statement or exclu-sion that time-tested and proven area practices are unsatisfactoryor inappropriate. Users of this manual are encouraged to contactNRCA members in their geographical areas for specific adviceconcerning area practices and current technical information.

The Green Roof System Guidelines section of this manual iscomposed of the following sections:

IntroductionThis section contains general definitions andinformation applicable to all green roof systems and definesthe green roof waterproofing membrane types NRCA recom-mends for green roof systems.

Green Roof SystemsThis section contains general informa-tion and definitions of the three common types of green roofsystems.

Green Roof System CharacteristicsThis section containsinformation about the performance attributes, environmentalbenefits and components of green roof systems.

DecksThis section contains information on the commontypes of decks used with green roof systems.

MembranesThis section contains material and installationinformation about green roof waterproofing membranes usedin green roof systems.

System ComponentsThis section contains general informa-tion about system components that are integral to the water-proofing, drainage, moisture retention and growth media usedin green roof systems.

AccessoriesThis section contains general information aboutsystem accessories such as inspection boxes, irrigation lines,overburden dividers and metal components used in green roofsystems.

Additional information about design considerations, low- andsteep-slope systems, care and maintenance, reroofing, stan-dards and water tests also is provided.

Construction details applicable to green roof systems are pro-vided in the Green Roof Systems Construction Details section ofthis manual.

NRCA suggests the Green Roof System Guidelines section of this manual be used in the design of green roof systems only after careful review of the General Green Roof ProjectConsiderations section of this manual and a number of criteriahave been carefully considered, including:

Climate and geographic location

A buildings intended use and design life expectancy

Exterior and interior temperature, humidity and use conditions

Code requirements


LEED considerations

Type and condition of substrate

Structural system

Slope and drainage


Green roof system type (e.g., intensive [deep]), including overburden

Accessibility and building configuration

Building movement

Type and amount of insulation, protection and drainage needed

Need for ventilation during installation

Compatibility with adjacent building and/or system components

Construction sequencing

Worker safety

Potential building additions

Odors generated by certain system application methods

Snow loads, water retention loads

Construction traffic

Penetrations

Landscape maintenance

These criteria play an important role in the ultimate success orfailure of every green roof system assembly and must be con-sidered by a designer to determine the appropriate componentsof a green roof assembly, applicable products and specifications,and construction details to be used.

In addition, a designer should be certain green roof systemproduct manufacturers requirements are taken into account, as well as requirements of applicable insurance, building codeenforcement and/or other regulatory agencies. It is recommend-ed that material manufacturers written specifications be cosult-ed during the design of a green roof system.

2. Green Roof Systems

The term green roofing is generally accepted as the descriptionof a roof system with a surface of landscaped plantings. NRCAdefines a green roof system as a roof area of planting/landscap-ing installed above a waterproofed substrate at any building levelthat is separated from the ground beneath it by a man-madestructure. A green roof system consists of a waterproofing sys-tem and its associated componentssuch as protection course,root barrier, drainage layer, thermal insulation and aerationlayerand an overburden of growth medium and plantings.

Green roofing should be differentiated from the construction-industry term green building. Green buildings are designed,constructed and operated to boost environmental, economic,

health and productivity performance over that of conventionalbuildings, according to the U.S. Green Building Council. Greenbuilding encompasses the full building envelope and the build-ings immediate surroundings.

A green roof system by association is a component of greenbuilding, but more specifically, it is a planted waterproofing sys-tem installed over a habitable space. NRCA considers a greenroof system the combination of a waterproofing system, itsassociated green roof components, and an overburden of growthmedium and plantings. The term green roof system does notinclude plaza deck systems (i.e., hard-scape areas), individualplanters or a water-protection system that can be identified as aroof or waterproofing system. Green roof systems are alsoreferred to as garden roofs, eco-roofs, vegetated roofs andnumerous other terms.

Regulatory agencies may describe green roof systems relativeto design and composition predicated on energy and environmen-tal incentives. NRCAs intent is to provide specific guidelines andrecommendations for decks, green roof waterproofing membranesand the intermediate system components of green roof systems.

A green roof system is a combination of roof system, water-proofing, and landscaping concepts and components. A basicprinciple of a green roof system is that it consists of a greenroof waterproofing membrane as the means to prevent moisturefrom entering a habitable building or space.

The following are differences between a green roof systemand a conventional waterproofing or roof system:

A green roof system needs to be compatible with the plantsand vegetation and must resist contamination from fertilizersand other chemicals and materials used in conjunction withthe vegetation.

A green roof system is more susceptible to mechanical damage and abuse, especially during installation.

A green roof system must be protected from the tools used tomaintain the overburden/vegetation.

A waterproofing roof membrane for a green roof system is notreadily accessible after the overburden is installed. Designersshould be more conservative with their design, membraneselection and detailing.

A green roof system is exposed to landscaping, cultivation,vegetation work and human error. The landscape portion of a green roof system will require periodic maintenance; maintenance workers should be made aware that they shouldnot damage exposed materials, especially the waterproofinglayer and flashings. Specific safety precautions may need to be followed by maintenance and landscaping trades working in a roof environment.

A green roof system is protected from ultraviolet (UV) exposure and impact but still is exposed to thermal and environmental changes.

NRCA recommends a green roof system incorporate a direct-to-deck fully adhered waterproofing system. NRCA recognizes agreen roof system can include a loose-laid or partially adhered

(e.g., gridded attachment) membrane. However, NRCA does notrecommend the use of these types of attachment methods forgreen roof systems due to the potential for leak travel. Leaktravel is the ability of water to migrate horizontally from the ini-tial point of water entry, which makes it more difficult to locate aleak source/point of entry. Once an unadhered membrane iscompromised/breached, water has the potential to get under themembrane, whereas a breach in a fully adhered membrane maynot allow moisture beneath the membrane. This reduces thepotential for a leak to occur.

A green roof system may incorporate an insulation layer. If aninsulation layer is included, the recommended location is abovethe green roof waterproofing membrane. The insulation layershould be high-density, have a high compressive strength andbe moisture-resistant. The waterproofing system must be able towithstand a moist environment for a prolonged period of time.

The substrate (i.e., structural deck) for the green roof water-proofing membrane should be sloped to provide positivedrainage. NRCA does not recommend tapered insulation underthe membrane.

NRCA recognizes there are green roof systems that incorpo-rate rigid board insulation and/or rigid tapered insulation beneatha membrane. However, NRCA does not recommend the use ofinsulation under a green roof waterproofing membrane for greenroof systems due the potential for leak travel and damage to theinsulation layer. This type of green roof system is fully adheredto the insulation or may be loose-laid and ballasted by the over-burden. If a green roof waterproofing membrane for a green roofsystem is fully adhered above the insulation layer, NRCA recom-mends a layer of rigid board, such as a water-resistant gypsumboard or cementitious board, be fully adhered to mechanicallyattached or fully adhered insulation prior to installation of themembrane.

If insulation is installed under a green roof waterproofingmembrane, it should be fully adhered or mechanically attached,not loose-laid. If a structural deck is not sloped, insulationinstalled under a green roof waterproofing membrane shouldinclude rigid tapered insulation to provide positive drainage.Because NRCA is concerned that insulation shrinkage mayoccur, the insulation board joints should be taped to preventgaps from occurring. Additionally, insulation installed under agreen roof waterproofing membrane must have adequate com-pressive strength to properly support the membrane and over-burden. Traditional roof insulations do not have the compressivestrength that is necessary to provide proper support for themembrane and overburden. The use of high-density, moisture-resistant insulation with a high compressive strength is recom-mended regardless of whether the insulation is above or below agreen roof waterproofing membrane.

Green roof system types are defined by the landscaping por-tion of the system. There are three types of green roof systems:extensive (shallow), semi-intensive (moderate depth) and inten-sive (deep). The green roof waterproofing membrane componentis the same in all three types; however, the other system compo-nents vary based on the plantings and landscaping placed abovethe waterproofing system. The selection of the plants and land-

scaping determines which system components are needed. Forexample, the type of root barrier, the membrane-protection layerand the water-retaining layer vary based on the plant selectionand landscaping.



Figure 3: Extensive (shallow) green roof system

2.1 Extensive (Shallow) Green Roof

Systems

Extensive green roof systems use a narrower range of specieslimited to herbs, low-growing grasses, mosses and drought-tolerant succulents such as seduma plant variety known for itstolerance for extreme conditions. These types of plants canpotentially be sustained in a growth medium layer as shallow as2 inches to 6 inches and can be designed for steeper slopes(slopes greater than 2:12 [9 degrees]). Saturated weights forextensive green roof systems can start at approximately 12pounds per square foot and increase from there. Extensive greenroof systems require a root barrier and a moisture-retentionlayer and generally do not require irrigation. A water reservoirlayer may not be required.

Extensive green roof systems can often be installed on exist-ing buildings without the cost of major structural alterations.However, it is suggested that an engineering analysis of thestructure supporting the roof system be performed.


Figure 4: Semi-intensive (moderate depth) green roof system

2.2 Semi-intensive (Moderate Depth)

Green Roof Systems

Semi-intensive green roof systems use a combination of plantspecies that may include small shrubs and species like grassesand herbs and are generally limited to low-slope structures of2:12 (9 degrees) or less. Use of these plants requires a growthmedium layer from 6 inches to 10 inches. Saturated weights forsemi-intensive green roof systems can start at approximately 40pounds per square foot and increase from there. Semi-intensivegreen roof systems have landscaping requiring more regularmaintenance than an extensive system but are limited in plantselection due to shallower soil depths, such as a sod grass lawn.These systems will require a reservoir layer and may require anirrigation system.


Figure 5: Intensive (deep) green roof system

2.3 Intensive (Deep) Green Roof Systems

Intensive green roof systems use a wide variety of plant speciesthat may include trees and shrubs and are generally limited tolow-slope structures of 14:12 (1.2 degrees) or less. Use of largeplants requires a deeper growth medium layer, typically 10 inch-es or more, which results in greater weight and a need for anincreased structural load capacity of the building. Saturatedweights for intensive green roof systems can start at approxi-mately 60 pounds per square foot and increase from there.Intensive green roof systems typically require a heavy root

barrier and often require irrigation. These systems will require areservoir layer. Additionally, an efficient drainage layer may berequired due to the quantity of water from irrigation and projectconditions.


3. Green Roof System

Characteristics

A green roof system can enhance certain performance attributesof an individual building. The system can also complement theenvironmental features of the immediate and surrounding areas.

3.1 Performance Attributes

Green roof systems have a number of performance attributes.They are as follows:

Growth medium depth and vegetation may increase thermalefficiency, particularly during warm months.

Interior noise levels may be reduced because of the increasedamount of sound-absorbing materials.

Membrane service life may be extended by reducing thermalshock and shielding UV exposure.

Green roof systems provide storm-water management, includ-ing water-quality benefits and flooding and erosion control.

Green roof systems can improve efficiency of roof-mountedphotovoltaic panels and reduce radiation from communicationtowers.

Green roof systems provide aesthetic benefits to occupantsand adjacent buildings.

Green roof systems may provide economic benefits in theform of rebates from planning and developmental agenciesand covenants.

Green roof systems are environmentally friendly.

Green roof systems can provide LEED benefits.

Green roof systems can reduce rooftop temperatures.

3.2 Environmental Features

Green roof systems provide a number of environmental features.They are as follows:

Improve local, particularly urban, air quality

Improve wildlife habitats and vegetation growth

Improve community green space and preserve ecological balance

Provide a microclimate for horticultural therapy

Mitigate urban heat island effects

3.3 System Components

The following is a list of common components used within agreen roof system:

Engineered soil-based growth medium with plantings

Filter fabric layer

Reservoir layer

Moisture-retention layer

Aeration layer

Moisture-resistant insulation

Drainage layer

Root barrier

Protection course

Green roof waterproofing membrane system

The design of the deck, green roof waterproofing membranesystem, protection course, drainage layer and root barrier (ifneeded) is dictated by the specific overburden type selected,either extensive (shallow), semi-intensive (moderate depth) orintensive (deep). Additionally, the design of these components isbased on dead and live loads, such as expected water retention(ice and snow loads), expected water drainage and the rootstructure of the plantings.

NRCA recommends waterproofing systems be fully adhered tothe substrate and be able to provide hydrostatic resistance basedon the expected amount of water drainage and retention. The pro-tection course must be capable of protecting the membrane dur-ing placement of overburden. A root barrier is required to resistroot penetration. The drainage and retention layers must provideadequate flow characteristics and retention ability to support thegrowth of the plantings in the overburden (e.g., the engineeredsoil-based growth medium). Moisture-resistant insulation can beincluded as fill to lighten the overall weight of the system, addthermal resistance to the green roof system and maintain a propergrowing and dormancy environment for plantings. It is suggestedgreen roof systems be internally drained.

4. Decks

Green roof assemblies include a structural deck, a green roofwaterproofing membrane and its ass

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