Fire Classification for Roof-Mounted PV Systems
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Until recently, the National Electrical Code was the only widely enforced code in North America with specific requirements for PV systems. This changed when the 2012 editions of several international codes incorporated PV-specific content. In addition to the new International Fire Code requirements for PV systems—some of which Fortunat Mueller discusses in detail in “Pitched-Roof Array Layout for Fire Code Compliance,” —the International Building Code (IBC) introduced fire classification requirements for roof-mounted PV systems.
The 2013 California Building Code (CBC) and the California Residential Code (CRC) subsequently incorporated the new fire classification requirements. Since no available products met the requirements, the California state fire marshal issued an addendum to Information Bulletin 14-002 on April 29, 2014, advising local code enforcement agencies to temporarily delay enforcement of fire classification requirements for roof-mounted PV systems until January 1, 2015. This delay allowed UL and industry stakeholders time to develop new standards and enabled module and mounting system manufacturers to test products to these new standards.
New Building Code Requirements
The new fire classification requirements for roof-mounted PV systems originate in Section 1509 of the 2012 IBC, “Rooftop Structures.” Subsection 1509.7.2 addresses fire classification: “Rooftop mounted photovoltaic systems shall have the same fire classification as the roof assembly required by Section 1505” [emphasis added].
Fire classification is a fire-resistance rating system for building materials. In some locations, such as California’s wildland urban interface (WUI) areas, building codes require the use of roof assemblies with enhanced fire-resistance ratings. Where this is the case, Subsection 1509.7.2 ensures that installing a roof-mounted PV system does not adversely affect the fire resistance of the roof.
Fire-resistance ratings for roofs. Per IBC Section 1505, roof assemblies are either nonclassified or fire classified. Nonclassified roof assemblies remain untested for fire resistance. Roof fire performance is classified by means of burning brand and spread of flame tests. Burning brand tests simulate what happens when burning embers fall on a roof surface. Spread of flame tests simulate how fire propagates across the roof. Fire-classified roofs are rated—in decreasing order of fire resistance—as Class A, B or C, based on their ability to withstand severe, moderate or light fire exposure.
Since Class A and Class B roofs provide higher fire resistance than nonclassified or Class C roofs, AHJs may require Class A– or Class B–rated roofs in areas with high wildfire vulnerability. For example, the City of Oakland implemented a mandatory Class A fire rating for all new residential roofs after the devastating 1991 firestorm. When California adopted the 2013 CBC and CRC on January 1, 2014, the number of jurisdictions with Class A and Class B roof requirements increased significantly.
Noted code expert Bill Brooks expects this trend to continue: “While current Class A and B fire rating requirements impact only about 20% of California, and only a few percent of the rest of the United States, it is likely that these percentages will rise dramatically over the next few years. The solar industry must be prepared to update its products to meet the demand for higher fire-rated roof systems.”
PV System Fire Classification
A key word in IBC Subsection 1509.7.2 is systems: PV systems—not modules—must carry a fire classification rating. Whereas legacy fire performance tests evaluated PV modules on their own, the new tests evaluate modules in concert with mounting system components. This represents a significant departure in how the industry evaluates PV system component fire performance.
Legacy approach. For nearly two decades, the industry evaluated and classified PV modules according to fire exposure tests outlined in UL 1703, “Flat-Plate PV Modules and Panels.” While the legacy fire performance tests for PV modules borrowed elements from fire exposure tests for roof assemblies, evaluators applied burning brand and spread of flame tests to PV modules in isolation rather than within the built environment. This approach ignores the racking assembly’s impact on the spread of flame. For example, the legacy fire exposure tests do not consider the potential chimney effect where PV modules are flush mounted above a steep-slope roof.