A series of large-scale experiments commissioned by the Building Safety Regulator (BSR) has revealed fire safety concerns regarding photovoltaic (PV) panels installed on pitched roofs
The research, carried out by the Health and Safety Executive(HSE), forms part of a technical review of Approved Document B (fire safety) and found that solar panels on pitched roofs can significantly influence fire spread, raising concerns for building safety and firefighting strategies.
“The aim of this work is to study how the installation of photovoltaic (PV) panels affects the fire spread over pitched roofs in residential buildings,” the report states. Eleven large-scale experimental tests were commissioned by the BSR technical policy team and were conducted at the HSE’s science and research centre to determine whether further guidance is needed in statutory fire safety documents.
Initial results indicate that all samples incorporating PV panels exhibited greater flame spread than control samples. “Even where the PV panel provided limited fuel to the fire, the cavity created by the solar panel allowed the flames to reach higher up the sample,” researchers observed.
The experiments compared building-applied PV (BAPV) panels with building-integrated PV (BIPV) systems. Plastic-backed PV panels (Class C, IEC 61730-2) showed “significant vertical fire spread up the array reaching the top of the panels,” though horizontal spread was limited. In contrast, glass-backed panels (Class A) performed better, with flames not extending beyond the first panel.
One test involving plastic roof tiles classified as BROOF(t4) under BS EN 13501-5 produced alarming results. “Flame spread on this sample was much greater than all other tests… with the entire area under the solar panels rapidly becoming involved in the fire and large flames produced above the top of the roof,” the report notes.
BIPV systems presented additional hazards, as “significant vertical and horizontal flame spread was observed in all of the plastic tray integrated systems,” with fires proving harder to extinguish due to cavities behind waterproof layers. “Part of the fire was contained in the cavity… meaning it was harder to apply water to this area unless the fire had burnt an opening,” the report stated, highlighting implications for fire service response.
Researchers also found that mounting rails on BAPV systems acted as fire breaks, slowing upward spread along the rear surface of panels.
Following these findings, four additional tests have been commissioned, including one to isolate the effect of PV panels on plastic roof tiles and three to examine fire penetration in BIPV systems. These will assess the role of fire-retardant breather membranes with different classifications (Class E, B, and A2).
The report concluded that when compared to BAPV systems, "the BIPV samples showed greater fire spread both horizontally and vertically,” underscoring the need for further investigation into design and safety standards.
This experiment update report provides critical insights into how PV panel design and roof materials affect fire behaviour. However, the release also explained that the full report for this work has not yet been produced, and it has been issued with the caveat that findings may evolve as data interpretation and validation are fully completed for all tests.
You can read the full update here.