Evaluation of Roof Coatings for Mitigating Fire Spread in Rooftop Photovoltaic Assemblies

ABSTRACT Photovoltaic (PV) power systems are increasingly deployed in commercial and residential settings, particularly on large, flat rooftops of warehouses and superstores, where they enhance energy efficiency and support sustainability goals. However, the presence of roof‐mounted PV panels can significantly increase flame spread during a fire, and large‐scale installations have contributed to a rise in roof fire incidents. These fires are challenging to suppress due to the electrical activity of PV panels, often resulting in substantial property damage and environmental harm. While fire test methods such as FM 4478 “Examination Standard for Roof‐Mounted Rigid Photovoltaic Module Systems” can identify fire‐safe roof constructions and PV panel assemblies, additional solutions are needed to mitigate fire risks on existing combustible roofs. This study systematically evaluated roof coatings as a passive fire protection strategy, beginning with a characterization of fire exposure using the ASTM E108 “Standard Test Methods for Fire Tests of Roof Coverings” Class A test on simulated rooftops and PV panel decks. Three representative roof constructions were tested alongside PV panels with either plastic or glass backsheets. Results from tests involving two types of roof coatings revealed that one coating effectively reduced fire spread by forming an encapsulating barrier that prevented ignition of pyrolysate generated during pyrolysis of roofing materials. These findings support the development of a new fire test method and examination standard for roof coatings.