The NRCA Roofing Manual: Membrane Roof Systems—2015 was released in March and updates and replaces The NRCA Roofing Manual: Membrane Roof Systems—2011. Other current volumes in The NRCA Roofing Manual include The NRCA Roofing Manual: Metal Panel and SPF Roof Systems—2012; The NRCA Roofing Manual: Steep-slope Roof Systems—2013; and The NRCA Roofing Manual: Architectural Metal Flashing, Condensation and Air Leakage Control, and Reroofing—2014.
The NRCA Roofing Manual is a best-practices guide for roof system installations in North America. NRCA's best practice approach generally is more conservative than building codes' minimum requirements and may be consistent with or more conservative than manufacturers' requirements.
Revised organization
If you have previous volumes of The NRCA Roofing Manual, you will notice the content flow has changed in the new volume. NRCA acknowledges its manuals are not read cover to cover. Consequently, this volume has been reformatted to be used as a reference manual with roofing contractors and roof system designers in mind. Guides for developing roof system specifications are placed in the first chapter where they can easily be located ahead of component-specific information.
Chapter 1—Roof System Configurations provides descriptions of how roof deck substrates, air and vapor retarders, rigid board insulation and roof membrane components are combined to design and construct membrane roof systems. A roof system designer may use this chapter to select a specific roof system application and immediately focus on component selection or compare different roof system configurations to determine the preferred system for a project, for example.
Roof system configurations in the manual are designated by roof membrane type, application method and substrate type. For example, a common re-cover configuration is designated "Mechanically Attached Thermoplastic Roof System, Existing Roof System." Chapter 1 provides roof system configurations for re-cover applications alongside new construction and roof system replacement configurations.
Each roof system configuration has a listing of applicable roof system components. For each roof system component, a reference is provided to the section in the manual where more detailed information about the component is located.
For each roof system component, a designer may select from provided material options. The options are designated by common industry names and corresponding ASTM International standard material specifications if available. For instance, high-density polyisocyanurate re-cover insulation board is identified as ASTM C1289, "Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board," Type II, Class 4 material.
Moving past the opening chapter, content is arranged similarly to previous volumes. Chapter 2 discusses roof deck materials. Chapter 3 provides considerations for air and vapor retarders installed as part of roof assemblies. Chapter 4 has guidelines for rigid board roof insulation and cover boards. Chapter 5 addresses roof membranes. Chapter 6 has information about fasteners used with membrane roof systems. Chapter 7 discusses roof membrane surfacings. Chapter 8 focuses on prefabricated accessories used with membrane roof systems. Chapter 9 provides guidelines for roof re-cover and replacement. And construction details are found in Chapter 10.
Updated insulation guidelines
Chapter 4—Rigid Board Insulation has a revised discussion of principles and terminology applicable to designing roof systems for thermal resistance. An example roof assembly R-value calculation is included to illustrate the application of these principles.
An updated discussion of tapered roof insulation explains how to comply with International Energy Conservation Code (IECC) provisions applicable to tapered roof insulation. Currently, IECC's 2006, 2009 and 2012 editions serve as the technical basis for energy codes adopted throughout most of the U.S. These model codes provide the same language applicable to determining the minimum tapered roof insulation R-value for code compliance purposes. The wording used to express the code's intent has caused confusion in the industry. Although IECC 2015 provides different wording, the code's intent remains unchanged. The revised manual text provides an explanation.
Material-specific recommendations regarding rigid board insulation products have been revised, and information about insulation materials not addressed in the previous edition of this volume also has been added.
This revision introduces information about asphalt core board and cement board and brings back composite board insulation information last included in The NRCA Roofing and Waterproofing Manual, Fifth Edition.
Asphalt core board has been used as a cover board over primary insulation and as a separation board in re-cover applications with polymer-modified bitumen roof membranes in Canada for a number of years. Recently, it was introduced to the U.S. market. According to manufacturers, polymer-modified bitumen sheets may be torched directly to asphalt core board.
Cement board, recently introduced to the U.S. roofing industry, is manufactured to comply with ASTM C1325, "Standard Specification for Non-Asbestos Fiber-Mat Reinforced Cementitious Backer Units," Type A sheets intended for exterior applications. This material is intended for use as a thermal barrier to provide fire resistance over steel roof decks and combustible substrates, substrates for air and vapor retarders, and cover boards beneath roof membranes.
Types of roof insulation materials also addressed in Chapter 4 are cellular glass, expanded polystyrene, extruded polystyrene, glass-faced gypsum, fiber-reinforced gypsum, stone wool, perlite, polyisocyanurate, high-density polyisocyanurate and wood fiberboard.
Because adoption of updated energy codes has driven an increase of insulation thickness in membrane roof assemblies, in this volume, NRCA has revised its recommendation for maximum polyisocyanurate insulation board thickness. NRCA now recommends roof system designers specify polyisocyanurate board insulation be installed in multiple layers with a 2.6-inch maximum board thickness.
Hot-applied asphalt
NRCA updated its recommendations for hot-applied asphalt. This follows a significant revision to ASTM D312, "Standard Specification for Asphalt Used in Roofing." The standard's revision, approved in December 2014 and designated ASTM D312-15, addressed NRCA's concerns with hot-applied built-up roof systems' viability in North America.
NRCA now recommends suppliers and installers of hot-applied asphalt roofing materials specify roofing asphalt that complies with ASTM D312-15.
For a detailed discussion of the updated standard, see "An updated standard," February 2015 issue, page 12.
More on single-ply membranes
In Section 5.4—Single-ply Roof Membranes, discussion of adhered membranes was expanded to address the available application methods such as adhering sheets with solvent-borne adhesives, water-based adhesives, foam adhesives and self-adhering sheets.
Also, roof system configurations using self-adhering thermoplastic sheets were added in Chapter 1. Self-adhering single-ply roof systems are an option to consider when a project requires an adhered thermoplastic roof membrane and liquid-applied adhesive applications are problematic because of limitations regarding the use of liquid-based adhesives.
The effects of air intrusion on design and installation of mechanically attached single-ply roof systems specifically are addressed in the single-ply section. Related recommendations for additional membrane securement were added to the Chapter 10—Construction Details introduction.
Other new information
Information about model code requirements for rooftop pipe supports was added to Chapter 8—Roof Accessories. Roofing contractors may be responsible for installing pipe support systems in reroofing scenarios.
An updated Chapter 9—Reroofing includes roof re-covering as well as roof system replacement considerations. Chapter 9—Roof Re-covering in the 2011 volume specifically addressed re-cover applications. The current chapter was assembled by combining the re-cover guidelines with membrane roof system replacement guidelines originally provided in The NRCA Roofing Manual: Architectural Metal Flashing, Condensation and Air Leakage Control, and Reroofing—2014.
Two new appendices round out the major additions in the new volume. Appendix 1—Wind Uplift is a primer on wind-uplift resistance design for roof assemblies in accordance with International Building Code provisions. Appendix 2 provides NRCA's guidelines for installation of rooftop photovoltaic components over low-slope membrane roof systems.
A good value
If you are involved with designing membrane roof systems, using the updated manual can offer a number of advantages.
The manual provides roof system configurations that reference up-to-date industry standards for materials and methods. Also, guidelines for complying with code requirements are based on provisions in the 2015 editions of the I-Code family of model codes and current editions of other codes commonly adopted by U.S. jurisdictions.
When you work with a manufacturer's specifications, the roof system configurations can help verify the specifications are complete and current. For instance, an architect unfamiliar with a manufacturer's specification can compare it with a corresponding configuration in the manual to see whether the specification adheres to best industry practices.
NRCA guidelines regarding specific components may help you address client questions about project specifications when, for example, a designer proposes an enhancement to an existing specification.
A necessary resource
NRCA continues to provide valuable technical information to roofing professionals. For more resources and technical manuals, visit shop.nrca.net.
Maciek Rupar is an NRCA director of technical services.
New ways of access
For the first time, The NRCA Roofing Manual: Membrane Roof Systems—2015 is available on Apple, Android and Windows tablets and for download from NRCA's online bookstore, shop.nrca.net.
The app version and online PDF are the new primary delivery formats for The NRCA Roofing Manual and jointly replace The NRCA Roofing Manual CD, which has been discontinued. The NRCA Roofing Manual: Membrane Roof Systems—2015 also is available in hard copy.
NRCA provides free access to the new manual to NRCA member companies and their employees. To access the app's content, a user will need his or her username and password for NRCA's website. To register for an account, go to www.nrca.net/account/register.
In addition, NRCA has made available its most-popular newsletters and publications in the app for free to members.
NRCA members also receive free electronic access to all NRCA publications in the NRCA bookstore, including the new manual. Members can download the manual as a PDF at shop.nrca.net.
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