Fire Class Rating of PV Systems

Solar ABCs research investigates whether and how the presence of stand-off mounted PV arrays may affect the fire class rating of common roof covering materials.  In particular, these tests were initiated in response to questions from stakeholders about the language in the UL Guide Card that stated that PV modules may or may not reduce the fire class rating of roof coverings when modules of a lower rating are installed above a roof covering with a higher rating All tests were conducted by UL in Northbrook, IL, with assistance from representatives of Solar ABCs.

In October 2013, the UL 1703 standard was changed to create a new fire classification rating test. Solar ABCs published a report, Fire Classification Rating Testing of Stand-Off Mounted Photovoltaic Modules and Systems, which describes the new test and the process to develop the test.


Since 2009, Underwriters Laboratories, with the support of Solar ABCs, has conducted research testing on issues related to the fire classification rating of PV modules and systems.

The following reports detail the tests and results.

Effect of Roof-Mounted Photovoltaic Modules on the Flammability of Roofing Assemblies, September 30, 2009, Revised March 5, 2010

This initial study measured the surface temperature and incident heat flux of a noncombustible roof with a noncombustible PV module surrogate installed at 10, 5, and 2.5 inches above the roof. In addition, limited burning brand and spread of flame tests were conducted using actual PV modules. These tests were designed to (1) develop baseline data on the fire exposure during standard tests for roof with no PV module according to UL 170, (2) determine the effect of varying selected PV installation parameters, and (3) document the impact of lesser fire rated PV modules on common roofing assemblies.

Effect of Rack Mounted Photovoltaic Modules on the Flammability of Roofing Assemblies – Demonstration of Mitigation Concepts, September 30, 2009, Revised February 10, 2010

In a continuation of the first study, several simple design concepts were devised to assess their effectiveness in improving the fire classification rating of the roof with a rack mounted photovoltaic module. The mitigation measures studied includes (1) use of flashing at the leading edge of the roof with control of separation between the roof and flashing, and (2) use of non-combustible back sheet.

Effect of Rack Mounted Photovoltaic Modules on the Fire Classification Rating of Roofing Assemblies, January 30, 2012

The second project further investigated rack mounted PV modules on roof decks to determine (1) the effect of PV modules mounted at angles (positive and negative) to steep and low sloped roof, (2) the impact of PV modules mounted at zero clearance to the roof surface and with the ignition source directed in the plane of the roof or the plane of the PV surface, and (3) the heat release rate and transfer to roof surface of Class A, B, C brands and common materials such as leaf debris and excelsior (wood wool).

Characterization of Photovoltaic Materials Critical Flux for Ignition/Propagation, January 16, 2012

The third project investigated the critical flux for ignition of roofing and PV products. While the individual values varied, most were within the range of the flux values measured on the roof in the original experiments with the PV module in place.

Determination of Effectiveness of Minimum Gap and Flashing for Rack Mounted Photovoltaic Modules, March 29, 2012

The fourth project was undertaken to validate the performance of two approaches thought to mitigate the effect of roof mounted PV modules on the fire ratings of roofs - a minimum separation gap and a sheet metal flashing to block the passage of flames between the PV module and the roof assembly.

Considerations of Module Position on Roof Deck During Spread of Flame Tests, July 24, 2012

The fifth project included a series of experiments to investigate a modification of the current UL 1703 spread of flame test to (1) expose a PV module to flames originating from the UL 790 (ASTM E108) ignition source, (2) allow those flames to generate on a representative roof section, and (3) observe the propagation of the flames underneath the candidate PV module being tested. The repositioning of the PV module was conducted to investigate an application of the first item (roof) / second item (module) ignition sequence. This concept was investigated to refine the understanding of the effect of a rack mounted PV array on the fire rating of a Class A roof.

Validation of 42" PV Module Setback on Low Slope Roof Experiments, December 12, 2012

The seventh project included a series of experiments to generate data in support of proposed changes to UL 1703, specifically, 42 inch setback of the PV module on low slope roofs. The results of this investigation could be used to validate performance of low slope roof test parameters as contained in a draft of a revised test method for consideration by the UL 1703 Standards Technical Panel (STP).

Validation of Roof Configuration 2 Experiments, February 12, 2013

The ninth project included a series of experiments to generate data on a complete PV assembly/roof configuration including rack and air deflection hardware.
The results of this investigation could be used to (1) validate performance of low slope roof test parameters as contained in a draft of a revised test method for consideration by the UL 1703 Standards Technical Panel (STP), and (2) provide quantitative data to support the proposed standard revisions, specifically, a PV assembly including a module, rack and air deflection hardware mounted on a standardized roof configuration representing roofs with minimal slope.

Report on Spread of Flame and Burning Brand Performance of Generic Installations,
January 23, 2014, Revised March 20, 2014

This study reports on fire rating performance of generic PV and racking systems when subjected to the revised UL 1703 PV system fire test. The results of this investigation maybe used to provide quantitative data to support future standard revisions proposals for PV assemblies as described in this report. It may also be used to provide industry a set of installation practices that enable meeting the fire performance requirements.

Building Integrated Photovoltaics

The work described above does not apply to Building Integrated Photovoltaic (BIPV) installations. Since BIPV become the roof, they must comply with the fire classification requirements for roof assemblies as described in UL Standard 790.

International Building Code

The 2012 International Building Code includes the following requirement: "1509.6.2 Fire Classification. Rooftop mounted photovoltaic systems shall have the same fire classification as the roof assembly as defined required by Section 1505."

A Solar ABCs White Paper, Impacts on Photovoltaic Installations of Changes to the 2012 International Codes, discusses the fire classification change and other code changes affective photovoltaic installations. 

The development of the 2015 Edition of the model codes developed by the International Code Council is underway. Code proposals were accepted to change the language in the 2015 International Building Code.

There is also an opportunity to submit Public Comments on the actions taken at the Code Development Hearings by the Code Development Committees, and those Public Comments will be heard at the Final Action Hearings on October 24-28, 2012 in Portland, Oregon.