December 28, 2018
by Trevor M. Weilbach, PE, and J. Eric Peterson, PE
Low-slope roofing systems are constantly changing and developing. Roofing manufacturers bring new products and assemblies to the market each year. These new products, as well as existing roofing systems, are applied over the most vulnerable location of a building’s envelope. In an effort to ensure each and every roofing assembly meets a minimum level of performance, Section 1503.of the International Building Code (IBC) requires, “Roof decks shall be covered with approved roofcoverings secured to the building or structure in accordance with the provisions of this chapter. Roofcoverings shall be designed and installed in accordance with this code and the approved manufacturer’s instructions such that the roofcovering shall serve to protect the building or structure.”
This approval process requires roofing systems and all their associated components be tested by an accredited third-party testing laboratory in their installed conditions to verify they meet minimum requirements. These tests and the associated code compliance reports are generated for each combination of components, attachment methods, and substrate conditions permitted for installation.
As defined by the International Code Council Evaluation Service (ICC-ES):
Evaluation reports are public documents, available free of charge on the worldwide Web, not only to building regulators and manufacturers, but also to contractors, specifiers, architects, engineers, and anyone else with an interest in the building industry. All of these people look to ICC-ES evaluation reports for evidence that products and systems are code-compliant.
Any combination of these variables that has not been tested and is not listed in a code compliance report will not have approval for use and does not comply with IBC if installed.
With regard to low-slope roofing systems, manufacturers provide instructions to contractors specifying the particular combinations of membrane assemblies, fasteners with placement patterns and spacing, adhesives with ribbon spacing, and other installation requirements (normally included in the standard installation instructions and material specification sheets) necessary to resist the design wind load uplift forces. The manufacturer’s installation instructions and material specifications, in conjunction with the information from the code compliance report, form the basis by which a contractor ensures the system being installed is acceptable for use per the code.
The application of the roofing must be consistent with how the systems were configured during testing. It is important to verify the information in the code compliance report and the manufacturer’s installation instructions are current and in agreement with each other and the system to be installed meets the requirements of both documents. If there are inconsistencies, they must be resolved before the installation proceeds.
A brief history of the ICC-ES
The International Code Council (ICC) was originally formed in 1994 by the three major code authorities located across the United States. Prior to the creation of ICC, model codes were maintained on a regional basis by Building Officials and Code Administrators International (BOCA), the International Conference of Building Officials (ICBO), and the Southern Building Code Congress International (SBCCI). The merger of these three bodies took several years to complete, and the first version of a national model building code was then published as the 1997 IBC.
Prior to and after the merger, each regional code authority had its own evaluation service for product testing. Those were known as the National Evaluation Service (NES), BOCAI Evaluation Services, ICBO Evaluation Service, and SBCCI Public Service Testing and Evaluation Services. On February 1, 2003, the four evaluation services combined to form ICC-ES, a subsidiary of ICC. At the time of the merger, the previous evaluation reports published by the founding agencies were still valid and were known as ‘legacy reports.’
Additionally, the legacy reports published by the parent companies prior to the merger remained in effect past the listed expiration date. However, these reports were only applicable where the specific codes referenced in that report were still in effect. ICC-ES is one example of an accredited third-party testing lab that reviews data provided by the manufacturer and verifies compliance with IBC.
While these reports are not always accepted by the authorities having jurisdiction (AHJs), they are widely accepted and regarded as the standard.
Roof system ratings
Roofing systems are rated based on testing completed by the manufacturer’s testing agency and verified by the evaluation service. Each building has a specific wind uplift design requirement based on calculated wind uplift pressures, taking into account parameters such as geographical location, building height and geometry, enclosure classification, and topographic factors (Figure 1). These design pressures are typically calculated either by following the requirements of American Society of Civil Engineers (ASCE) 7, Minimum Design Loads for Buildings and Other Structures, or if Factory Mutual (FM) certification is required for insurance purposes or other reasons, the provisions for determining wind uplift forces outlined by FM 1-28, Wind Design.
IBC requires the calculation of wind pressures for components and cladding elements, including the roof membrane. The intent of the components and cladding calculation is to ensure veneers, windows, roofing systems, soffits, and other nonstructural components are adequately fastened to the structure and they continue to function during a design wind event (To see an example of a roofing failure, click here.). The designer calculates the required uplift pressure in pounds per square foot and matches it with the tested uplift capacity of that specific roofing system and configuration of supporting substrate and insulation. Important variables to consider include, but are not limited to:
To gain approval and compliance with the code, the manufacturer engages a testing lab to perform the testing required by IBC. Once this is completed and maximum capacities are also developed, the manufacturer sends the data, along with other pertinent information, to ICC-ES or another accredited code compliance authority and submits an application for a compliance report. ICC-ES then reviews the data provided and validates compliance with the code. Upon a successful review and validation process, an evaluation report (ESR) is written and issued for the products and assemblies as previously described.
For low-slope roofing, the published report typically contains a series of tables presenting the materials and attachment methods for each tested system to allow the designer to select one with greater capacity than calculated demand. A generic example of what these tables typically look like is presented in Figure 2. The ESR is only applicable to the codes specifically referenced in the document since the code and testing requirements may change over time.
The following is an example of how failure to properly verify a roofing system’s compliance with the required code compliance report can result in installation of a system that does not meet code requirements. A three-ply modified bitumen (mod-bit) roofing system was installed on a multifamily residential complex located in the southeastern region of the United States. The design of the complex was completed in 2006 and construction was completed in 2007. The 2003 IBC was in effect at the time of design and construction.
The designer specified the roof system to be installed in accordance with an outdated code compliance report: a legacy report published by ICBO in 1997. This was atypical, as the design professional generally provides only the uplift performance requirements. However, it does happen in private construction, where a designer chooses a specific system to specify for the project.
The testing that was completed and would have been reviewed to issue this compliance report was based on the 1994 Uniform Building Code (UBC) with 1996 accumulative supplements, not the 2003 IBC. Therefore, the designer incorrectly specified an outdated compliance report for the installation of the roofing system. Had the contractor installed the roofing system in accordance with this version of the report, the result would have been the installation of a system that did not meet the minimum requirements of the 2003 IBC.
Several years after the building was constructed, an investigation was conducted in response to several roof leaks and other serviceability problems that had been discovered throughout the structure. Some examples of defects observed in the roofing included inadequate fastener spacing, inadequate or incorrect lap splices, incorrectly seamed cap sheets, incorrect base sheet materials, loose and unadhered cap sheets at the parapets, and failed parapet flashings.
During the review of the project documentation, copies of the manufacturer’s product data sheets and installation instructions from the time of construction were obtained and reviewed. Through review of the contractor’s invoices, it was also discovered there were products used in the roof construction that were not listed in the project documents or the referenced legacy report. These included an interply membrane and fasteners for the base sheet other than those listed for acceptable use. The legacy report also made no mention of the applicability of OSB roof decking, which was installed below the roof assembly. It was clear the installation was not in accordance with the incorrectly specified legacy report.
The appropriate ICC-ES report complying with the 2003 IBC was issued in 2006, shortly after the start of the roof installation, indicating the manufacturer did not have an approved code report for the 2003 IBC at the time of the contractor’s bid for construction. As it turned out, the manufacturer had also not obtained code compliance reports for the installed assembly for the prior applicable code cycle in effect for this region: the 2000 IBC. Had this system been vetted at the time of construction, it would (or should) have been rejected as a non-code compliant system.
As mentioned, an AHJ will typically accept ICC-ES reports to confirm a system complies with the code. However, the report alone is not enough to ensure the system is constructed in accordance with code—it presents generic capacities of the assembly. The designer must ensure project-specific loads are calculated and use an assembly with greater capacity than demand.
If the 2006 ICC-ES report had matched the manufacturer’s materials and installation instructions that were used at the time of construction, and the system had been installed in strict accordance with these documents and other criteria listed in the report, it could have been verified the construction complied with the minimum standards necessary to meet the 2003 IBC. However, the site investigation revealed the roofing assembly installed was not specifically listed as an approved roofing assembly within either the ICBO legacy report or the appropriate 2006 ICC-ES report. Additionally, there were numerous inconsistencies between the code compliance reports, the manufacturer’s installation instructions, and the installed products regarding the fastener spacing and type, parapet and flashing details, and cap sheet requirements, among other aspects. Thus, compliance with the applicable code could not be verified.
When a designer elects to specify a particular roofing manufacturer and assembly, it is important to verify the system has a code compliance report appropriate for the applicable code in place for the project. If the designer does not specify a particular manufacturer and assembly, the installer should be required to submit a current code compliance report. The designer should then verify during the submittal review process the system materials, design configuration, load capacities, and installation requirements from the manufacturer are consistent with the design intent and submitted code compliance report.
Manufacturers must obtain updated code compliance reports for roofing assemblies that have been tested and confirmed to meet the minimum building code requirements. The manufacturer must also publish current installation instructions consistent with the tested and approved assemblies listed in the code report and make them available to the installers.
The roofing installer should identify inconsistencies between the contract documents, the installation instructions, and code compliance reports and seek clarification prior to installing a roofing assembly that does not conform with the code. The installer must then furnish and install the assembly in strict accordance with the appropriate manufacturer’s installation instructions and any specific requirements listed in the code reports, such as the specified substrate, components, and attachment methods.
The code compliance reports must be intimately understood by all parties in the design and construction process. Without understanding and strictly adhering to these fundamental design and construction procedures centered around the code compliance reports, the roofing system provided to the building owner and its occupants may not meet the minimum standards required by the building code.
Trevor M. Weilbach, PE, is a project engineer with WDP & Associates Consulting Engineers. He has four years of experience working on a variety of buildings in different phases of their service lives. Weilbach manages water infiltration investigations and performs repair designs to address as-built deficiencies. He has been involved in several roofing-related projects, including those centered on low- and steep-slope systems. Weilbach’s projects have ranged from higher education to single- and multifamily residential. He can be reached via e-mail at firstname.lastname@example.org.
J. Eric Peterson, PE, is principal of WDP & Associates Consulting Engineers. His more than 25 years of experience consist of various structural, material, and architectural engineering activities, specializing in building enclosure and roofing systems, nondestructive testing and design, and repair of concrete and masonry structures. Peterson performs a wide variety of building investigations, as well as structural inspection, analysis, and design, construction document development, and peer reviews of building enclosure systems related to waterproofing and roofing designs. He has been previously admitted as an expert witness for roofing-related disputes and has offered expert testimony in roof litigation projects. Peterson can be reached via e-mail at email@example.com.
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