Appropriate use of code compliance reports in roofing

Modified bitumen (mod-bit) roofing system installed over oriented strand board (OSB) roof decking.
Modified bitumen (mod-bit) roofing system installed over oriented strand board (OSB) roof decking.

Case study

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The designer specified the roof system to be installed in accordance with an outdated code compliance report: a legacy report published by ICBO in 1997.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 Therefore, the designer incorrectly specified an outdated compliance report for the installation of the roofing system.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.

Failed flashing and roofing patches at an interior corner.
Failed flashing and roofing patches at an interior corner.

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.

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