Recommended Readings

Recommended Readings

The NRCA Green Roof Systems Manual 2007 Edition

A green roofing resource

By James R. Kirby, AIA

Graphics Courtesy Professional Roofing Magazine

Publishers Note: This article was originally printed in the April 2008 issue of Professional Roofing Magazine, published by the NRCA.

W ith the proliferation of the sustainability movement within the construction industry, green roofing is touted as one of the ways to make roof systems more environmentally friendly. Recognizing this trend, NRCA began developing a green roofing manual in 2004. And in 2007, NRCA published The NRCA Green Roof Systems Manual—2007 Edition.

The manual provides in-depth information about green roof system projects. The information contained in the manual was developed by NRCA member contractors and applies to roofing contractors, designers, manufacturers, and third-party individuals involved with green roof system design and installation.

Although some information is provided about green roof system components, such as drainage layers, moisture-retention layers and filter fabric, if you use the manual, you primarily will find specific information about selection, design and installation of waterproofing membranes appropriate for green roof systems.

The manual

The manual is divided into four main sections: General Green Roof Project Considerations, Green Roof System Guidelines, Green Roof System Construction Details and Glossary.

Considerations

The General Green Roof Project Considerations section provides an overview of general information concerning the design and installation of quality green roof systems. The information is intended to complement The NRCA Roofing Manual series and should be used as a guideline to prepare proper specifications.

The manual defines a green roof system as a roof area of plantings/landscaping installed above a waterproofed substrate at any building level that is separated from the ground beneath it by a man-made structure. A green roof system consists of a waterproofing system and its associated components—such as protection course, root barrier, drainage layer, thermal insulation and aeration layer—and an overburden of growth medium and plantings.

As with all roof system types, proper design, quality materials and quality workmanship are needed to achieve a green roof system that will perform satisfactorily for its anticipated service life. Appropriate maintenance during a green roof systems service life also is necessary to ensure its success.

Recommended Readings

Also provided in the General Green Roof Project Considerations section is information about pre-bid and pre-job conferences; material storage and handling; temporary green roof waterproofing systems; weather considerations (such as high- and low-temperature installation, wind and precipitation); deck and structural design considerations; surface inspection; slope and drainage; expansion joints and control joints; curbs and penetrations; flashings (such as membrane base flashings, sheet-metal counterflashings and terminations); quality assurance and water testing; overburden; warranties; and recommendations for building owners.

Guidelines

The Green Roof System Guidelines section provides in-depth technical information about green roof systems design and installation; however, NRCA recognizes green roof system practices vary considerably throughout the U.S. because of the variety of conditions that exist and various roofing materials available.

Selected plant varieties commonly dictate a green roof systems necessary depth of growth medium. This also helps guide the specific component design.

Of course, when reroofing with a green roof system, a roof decks structural capacity should be considered. Because of the varying depths of growth medium, NRCA s manual divides green roof systems into the following three primary categories:

  • Extensive (shallow): a green roof system with an engineered soil-based growth medium approximately 2 to 6 inches deep
  • Semi-intensive (moderate depth): a green roof system with an engineered soil-based growth medium approximately 6 to 10 inches deep
  • Intensive (deep): a green roof system with an engineered soil-based growth medium greater than 10 inches deep

A fundamental idea behind the manuals development is that a green roof system is a combination of waterproofing and roofing concepts. Because a green roof system is likely to have moisture present within the system most or all the time, NRCA considers a waterproofing membrane appropriate. And because green roof systems include detailing similar to all other roof system types (parapet walls and roof drains, for example), construction details for green roof system waterproofing membranes are based on termination concepts NRCA considers appropriate for all roof system types.


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