By Mike Ennis, RRC
Construction specifiers are in a unique—and often demanding—position on the building team. Not only must they be familiar with various low- and steep-slope roofing systems, but they also need to address code requirements, sources of moisture not related to the roof, and a plethora of cladding, masonry, and sealant issues. Add to this the rapid growth of vegetative roofs, building-integrated photovoltaic (BIPV) solar systems, and sustainable roof designs, and many construction specifiers are on a stressful road to information overload.
Fortunately, associations like Single-ply Roofing Industry (SPRI) are helping with roofing research and standards-writing efforts geared to enhance current roof design knowledge and best practices. For more than 30 years, SPRI has represented sheet membrane and component suppliers to the Canadian and U.S. commercial roofing industry. As an accredited American National Standards Institute (ANSI) canvasser, SPRI has the unique ability to help develop standards for acceptance into international building codes. Over the past several years, SPRI has developed 12 ANSI-approved standards, three of which have been adopted by the International Building Code (IBC).
A major effort at codes consolidation resulted in the creation of the International Code Council (ICC) in 1994, which produces and publishes the IBC. Standards development organizations like this are major contributors to construction regulations in Canada. The National Building Code of Canada (NBC) and provincial building codes reference several U.S. standards, including aspects of IBC, giving these standards force of law in jurisdictions where the Canadian code is adopted.
This article examines three hot topics in roofing—updated insurance requirements, vegetated roofing standards, and wind effects—and explores how SPRI resources can be employed to better understand the impact on Canadian projects.
Recent FM changes and their rationale
Besides developing meaningful standards for the roofing industry, SPRI takes a keen interest in technical issues affecting design professionals, and much of the association’s efforts involve education. One of SPRI’s more recent initiatives involves revisions to Factory Mutual (FM) 4470, Single-ply, Polymer-modified-bitumen Sheet, Built-up Roof (BUR), and Liquid-applied Roof Assemblies for Use in Class 1 and Noncombustible Roof Deck Construction.1
In October 2012, FM Approvals officially notified roofing system manufacturers and component suppliers of the revised FM 4470. These changes mostly involve roof decking and went into effect on December 31, 2012. They include new testing requirements listed in FM Standard 4450, Class 1 Insulated Steel Deck Roofs. While the changes are of interest to all specifiers, it should be noted FM Approvals is a member of the FM Global Group—a commercial and industrial property insurance company. In other words, FM 4470 must only be followed when FM Global-insured buildings are having roof systems installed.
Nevertheless, the revisions to FM 4470 can have a significant impact on Canadian projects insured by FM Global, as well as other buildings where the standard is specified by the designer of record. FM Class 1 is sometimes used by architects as a ‘catch-all’ to ensure the roof deck assembly is subjected to a series of tests, including those required in FM 4470.
It seems likely FM believes its changes to this standard will reduce insurance risk and provide greater safety factors on the company’s insured buildings. Over the years, the number of roof fasteners required on the corners and perimeters of mechanically attached roof assemblies has been increased to meet design wind loads. It now appears FM Approvals is looking at the roof system/roof deck interface with an eye toward reducing the stresses on steel roof decking.
In fact, FM Approvals’ notification letter states the following new requirements have been added to Standard 4470:
Stresses induced to steel roof decking shall be determined by rational analysis and shall not exceed the allowable stresses per the latest edition of the North American Specification for the Design of Cold-formed Steel Structural Members, AISI S100-2001 … [and] … Limits on roof deck fastener stress have also been added.
Additionally, FM Approvals is conducting a full review of all current RoofNav-approved steel deck assemblies that, in its opinion, “overstress the deck.”2
SPRI encourages Canadian specifiers to ensure FM Approvals provides direction on the steel decking, and confirms the proposed design is acceptable for the project. For roof re-cover applications, SPRI recommends specifiers confirm with the applicable FM Approvals field office if a recover application is acceptable, or if the roofing system will have to be removed down to the steel deck.
It is also advisable to confirm with the applicable FM Approvals field office what roofing products are considered “rigid cover board.” As of June 2012, FM Approvals defines this material as:
A hard, dense board, which, in the sole judgment of FM Approvals and through testing, has demonstrated the ability to act in a composite manner with the steel deck to increase the Moment of Inertia and the Section Modulus and thus the wind uplift capacity of the roof assembly.
However, FM Approvals has not provided a list of acceptable products as of this article’s writing.
On non-FM-insured buildings, it is important to remember FM 4470 is not codified. The model code for all provincial building codes, the 2015 NBC may also allow wind uplift testing to be conducted in accordance with Canadian Standards Association (CSA) A123.21-10, Standard Test Method for the Dynamic Wind Uplift Resistance of Membrane-roofing Systems.
As always, when a design pressure is specified for the project, third-party certification from the roof system manufacturer can be provided. This can take the form of a test report from an accredited lab, ICC Evaluation Service (ES) report, or Underwriters Laboratories (UL) online certification directory. Unlike the newly revised FM 4470, however, these other entities document compliance using codified standards.
By not referencing FM 4470 and FM Approvals nomenclatures (e.g. FM 1-90, 1-120, etc.), Canadian designers may well avoid ambiguous specifications between the building code requirements and FM Approvals recommendations and/or requirements.
SPRI harvests knowledge about vegetative roofs
There is an increasing emphasis on sustainable roofing systems, and SPRI has helped with a wide variety of research studies, codes, and standards on vegetative green roof systems. In 2010, ANSI approved the first of three standards for vegetative roofs: ANSI/SPRI VF-1, External Fire Design Standard for Vegetative Roofs. This standard will also be included in the 2015 edition of IBC. It includes fire-control designs to limit the spread of flame should a vegetative roof system catch fire. The standard uses barriers of non-vegetative zones (e.g. firestop walls and fire-break roof areas) to contain a potential fire.
A second SPRI vegetative roof standard was approved by ANSI on June 3, 2010. ANSI/SPRI RP-14-2010, Wind Design Standard for Vegetative Roofing Systems, provides design guidelines associated with wind uplift and stone ballast scour. The standard also defines items such as setbacks from the edges of roofs in areas with high winds, use of wind erosion mats, and edging details. There is also a discussion of the various types of vegetative roof materials and their behaviour under varying wind conditions.3
SPRI has also successfully developed a third vegetative roofing document, working with Green Roofs for Healthy Cities (GRHC)—a root penetration standard for vegetative roof systems. ANSI/GRHC/SPRI VR-1, Procedure for Investigating Resistance to Root Penetration on Vegetative Roofs, was approved by ANSI in March 2011.4 The test described in this standard has been developed to evaluate a roofing material’s ability to resist normal root or rhizome penetration through a root protection barrier, or waterproofing layer. It is based on the German FLL’s “Procedure for Investigating Resistance to Root Penetration at Green Roof Sites.”
In another effort to better understand the performance of vegetative roofs, SPRI and the U.S. Oak Ridge National Laboratory (ORNL) completed a study showing vegetative roofs can help lower heat gain and losses, resulting in significant energy savings in mixed climates. The reduction in heat gain in cooling-dominated periods—and heat losses in heating-dominated periods—shown in the study translates into lower heating and cooling demands for the conditioned space (Figure 1).
The study notes the energy savings offered by vegetative roofs are climate-dependent and affected by the efficiencies of heating/cooling equipment. ORNL’s testing took place in the mixed climate of East Tennessee. In Canada, vegetative roofs will be of greater benefit on the heat-loss side of the equation, especially when compared to white roofs.
The ORNL research project was initiated by SPRI to quantify the thermal performance of various vegetative roof systems relative to black and white roofs—ethylene propylene diene monomer (EPDM) and thermoplastic polyolefin (TPO), respectively. Its results show lower roof membrane temperatures and fewer fluctuations experienced by the vegetative system than the control black and white assemblies. The decrease in roof temperature fluctuations is of benefit in all climates. However, there is still some debate about the energy efficiency of black versus white roofs in Canada. Generally, darker-coloured roofs may offer beneficial heat gain in winter, and may also lessen the need for snow removal.
“As part of the effort to reduce energy use in commercial buildings, energy codes are greatly increasing the required thermal efficiency of roofing systems,” explained ORNL’s Andre Desjarlais. “It is important to understand the energy savings associated with vegetative roofs so they can be properly credited in these codes.”
SPRI takes lead role in wind testing
The effect of high winds on roofs is a complex phenomenon, and inadequate wind uplift design is a common factor in roofing failures. Damage from wind events has historically been dramatic, and wind-induced roof failure is one of the major contributors to insurance claims. The biggest news on the wind design front in the past few years was the approval of ANSI/SPRI/FM 4435/ES-1, Wind Design Standard for Edge Systems Used with Low-slope Roofing Systems.
This standard provides the basic requirements for wind-load resistance design and testing for roof-edge securement, perimeter edge systems, and nailers. It also provides minimum edge system material thicknesses that lead to satisfactory flatness, and designs to minimize corrosion.
Construction professionals can use the standard, along with the specifications and requirements of roofing and edge material manufacturers (excluding gutters) for their wind designs. The current version of ES-1 includes updated performance requirements and has been expanded to include requirements addressed in FM 4435, Wind Design Standard for Edge Systems.
This revision of ES-1 not only incorporates components of FM 4435, but also addresses many of the questions and concerns raised about ES-1 over the years. Among other things, the ANSI/SPRI/FM 4435 ES-1 standard deals with roof edge securement to help prevent it from becoming a potential weak spot in low-slope roofing performance. ES-1 provides the basic requirements for wind-load resistance design and testing for roof-edge securement, perimeter edge systems, and nailers. It also sets out minimum material thicknesses that lead to satisfactory flatness, and includes designs to minimize corrosion.
SPRI knew recent post-hurricane investigations by the Roofing Industry Committee on Weather Issues (RICOWI) and FM Approvals consistently showed, in many cases, damage to a low-slope roof system during high-wind events begins when the edge of the assembly becomes disengaged from the building. Once this occurs, the components of the roof system (membrane, insulation, etc.) are exposed. Damage then propagates across the entire roof system by peeling of the roof membrane, insulation, or a combination of the two. For this reason, SPRI’s landmark ES-1 standard is currently referenced in Section 1504.5 of the IBC, and is relevant for the high winds experienced throughout Canada, particularly the Maritimes.
In addition, ANSI/SPRI WD-1 2012, Wind Design Standard Practice for Roofing Assemblies, was reapproved by ANSI last year. SPRI’s revised document complies with the current American Society of Civil Engineers (ASCE) 7-10, Minimum Design Loads for Buildings and Other Structures, which was significantly revised in 2010. These changes affect every roofing professional who uses ASCE for determining wind loads on structures, including many Canadian engineers. Some of the revisions include new wind speed maps using a 700+ year return; reinstating Exposure Category D for hurricane-prone coastlines, and “simplified” procedures for determining wind pressures for buildings of all heights.
SPRI’s focus this year remains the same—providing unbiased technical information to enhance the community of knowledge among specifiers, and help advance the roofing industry as a whole.
For example, ANSI recently approved a nuclear moisture testing protocol developed by SPRI with the help of RCI. ANSI/SPRI/RCI NT-1 2012 contains information on proper handling of nuclear-based moisture-survey equipment in the field, as well as calculating and analyzing survey results.
SPRI’s initiatives for the immediate future include a test program to evaluate moisture condensation under white and black roofing membranes. A second task force is leading the development of a roofing industry position on the use of lightweight structural concrete as a roof deck.
1 Several months ago, SPRI published two detailed bulletins that include recommendations for the designer, consultant, and contractor communities on important changes made to the standard. The SPRI Bulletins, an Excel worksheet and an executive summary, are available at www.spri.org/publications/policy.htm. (back to top)
2 For more on this topic, see the article, “The Rise in Green Roof Standards,” by Kelly Luckett, GRP, LEED AP, and Damon van der Linde, in the September 2010 issue of Construction Canada. (back to top)
3 RoofNav is a web-based specifications tool for roofing professionals created by FM Approvals. (back to top)
4 All three documents are available for viewing and free download at www.spri.org/publications/policy.htm. (back to top)
Mike Ennis, RRC, joined Single-ply Roofing Industry (SPRI) in 1993, becoming its technical director in 2007. He has chaired various SPRI committees and task forces, serving as president from 2004-2006. Ennis can be reached at firstname.lastname@example.org.