Research and analysis

Fire safety: Thermal exposure to roofs from fires involving photovoltaic panels (executive summary)

Published 22 December 2025

Applies to England

1. Background

This research was conducted under the Investigation of Real Fires project, commissioned by the Department for Levelling Up, Housing and Communities (contract reference CPD/004/122/039), and subsequently transferred to the Health and Safety Executive in its role as the Building Safety Regulator. The contents of this report, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect government policy.

2. Executive summary

This literature review, commissioned by the Building Safety Regulator and prepared by OFR Consultants, investigates the fire safety implications of photovoltaic panels (PV) installed on rooftops. It consolidates experimental findings, international incident data, and current regulatory frameworks to evaluate the extent to which rooftop PV systems alter fire dynamics and pose additional risks to roof constructions and firefighting operations. The rapid expansion of PV technology, driven by global decarbonisation efforts, has introduced new fire hazards in the built environment. Two primary forms of PV systems are addressed:

• building-applied photovoltaic systems (BAPV), which are retrofitted to existing roofs
• building-integrated photovoltaic systems, which are building elements that also function as PVs

This review places particular emphasis on BAPV systems due to their increasing prevalence and complex interactions with existing roof constructions. Key fire safety concerns include the alteration of thermal exposure patterns caused by PV modules, which often create semi-enclosed spaces between the roof and the PV panel, that trap heat and redirect flames towards the roof surface. Experimental studies consistently show increased heat fluxes of up to 50 kW/m² beneath PV arrays, significantly exceeding the 12.5 kW/m² considered in standard test methods such as BS EN 13501-5. These conditions have been shown to facilitate fire spread across roofing membranes previously deemed adequate under current classifications. The review identifies a range of parameters that influence fire behaviour in PV roof systems, including gap height between the PV panel and roof, panel inclination and geometry, roof construction materials (e.g., insulation and membrane types), array configuration and array spacing. Experimental research demonstrates the existence of critical thresholds, such as gap height, beyond which flame spread is either minimised or exacerbated. For instance, flame spread may accelerate by a factor of 38 when gap height falls below critical limits due to enhanced heat retention and re-radiation, when compared to a scenario without a PV. These findings of changes in fire dynamics are consistent across multiple independent studies conducted at medium and large scales. The review also highlights that existing classification tests and building guidance in England (e.g. Approved Document B and CEN/TS 1187 Test 4) do not fully capture the unique fire dynamics introduced by PV arrays. These tests assess roof coverings in isolation and do not account for the modified fire scenarios introduced by PV system geometry, installation techniques, or system-wide behaviour. In addition to technical and experimental insights, the review draws attention to practical challenges for emergency responders. PV systems operating on direct current, introduce persistent electrical hazards even after power disconnection. The presence of PV arrays can also obstruct firefighting access to the fire under the PV panel, impair ventilation systems, and if combined with battery storage, pose chemical or explosion hazards. Several recommendations are proposed in light of the findings:

• use of non-combustible roof coverings beneath PV arrays
• fire-resistant construction from the exterior inward to mitigate roof penetration
• design guidance for PV layout, including minimum gap heights and array segmentation to limit flame spread and ensure compatibility with compartmentation and smoke venting
• development of new test methods that accurately reflect the modified fire conditions created by PV systems

Given the current regulatory and technical gaps, the review concludes that enhanced design practices and possible updates to testing and classification systems warrant further research to ensure rooftop PV installations do not compromise fire safety in the built environment. This should then lead to changes in technical policy.