Researchers at the Danish Institute of Fire and Security Technology (DBI) have released the results of initial tests investigating how a 12 mm cement-bonded particle board (CPB), installed between a combustible roofing membrane and the underlying insulation, affects fire development. They found that the CPB can reduce the likelihood of self-sustained flame spread beneath rooftop PV systems.
The researchers classify the rooftop installations as building-applied photovoltaic (BAPV) systems, in which PV modules are added to the building envelope, as opposed to building-integrated photovoltaic (BIPV) systems, in which the PV components form part of the building envelope itself.
The analysis is based on seven tests commissioned by Germany’s Rigid Foam Industry Association (Industrieverband Hartschaum, IVH) and the Association for European Manufacturers of Expanded Polystyrene (EUMEPS). The tests were conducted at the Troned Training Factory at the Twente Safety Campus in the Netherlands between October 2024 and April 2025.
Certification and testing specialist Kiwa BDA conducted the tests and provided six test reports to IVH and EUMEPS. The two associations subsequently shared the reports, test videos and thermocouple data with DBI, whose researchers also witnessed all seven tests in person.
“The growing deployment of rooftop PV makes it increasingly important to address fire safety at the system level,” Emanuela Gallo, EU technical affairs manager at EUMEPS, told pv magazine. “Our tests indicate that fire behavior depends on the interaction between the roofing membrane, protective layers, insulation and PV system configuration, rather than on the properties of an individual component alone.”
All tests were performed on square roof assemblies measuring 7 m × 7 m, with non-ballasted, east-west-oriented PV arrays. The first four tests used four modules in a 2 × 2 configuration, while the subsequent three used 12 modules in a 4 × 3 configuration.
In all tests, a 15 kW gas burner served as the initial ignition source and operated for 10 minutes. The square burner was positioned 80 mm above the roof surface beneath a PV module at the corner of the array and at the midpoint of the module’s long edge. The horizontal distance between the module’s lowest edge and the nearest edge of the burner was 120 mm.
The seven tests were divided into three groups to assess the effect of adding a 12 mm CPB to the roof assembly.
The baseline test used a 1.8 mm PVC roofing membrane, two layers of glass fleece and EPS insulation, without CPB. The EPS insulation ranged from 100 mm to 260 mm in thickness to reflect different building energy requirements, although the researchers did not assess the effect of total insulation thickness on fire behavior.
Four tests used a similar configuration but added the 12 mm CPB between the PVC membrane and EPS insulation.
Two reference tests examined alternative roofing materials and insulation. One replaced the PVC membrane with an 8.2 mm-thick combined bitumen roof covering while retaining the CPB and EPS insulation. The other used the PVC membrane with mineral wool insulation instead of EPS and did not include the CPB.
The baseline represented a roof with a load-bearing concrete deck, while the other configurations represented lightweight roof assemblies supported by trapezoidal steel decking.
Thermocouples were installed at selected interfaces within the roof assemblies to measure temperatures and complement visual observations during and after the tests. Each test used 27 or 30 thermocouples, depending on whether the PV array comprised four or 12 modules.
The seven tests produced three outcomes: flame spread beneath all PV modules and into the insulation, flame spread beneath all modules without reaching the insulation, or no self-sustained flame spread after the burner was switched off.
None of the tests showed significant self-sustained flame spread beyond the PV array.
In the baseline test, fire spread beneath all four modules and initially ignited the EPS insulation. The EPS, however, melted away from the flames and self-extinguished, preventing further propagation within the insulation.
Adding the 12 mm CPB between the PVC membrane and EPS insulation prevented self-sustained flame spread in three of the four tests, with fire damage remaining localized around the module above the gas burner. In the fourth test, flames spread beneath all PV modules, an outcome the researchers attributed to higher wind loads. Even in this case, the underlying EPS was affected only directly beneath the burner.
According to the researchers, the results indicate that the CPB acted as a heat sink, absorbing thermal energy and reducing heat transfer to the EPS insulation.
When the PVC membrane was replaced with the thicker bitumen roof covering, flames again spread beneath all modules, although damage to the EPS remained confined to the area beneath the burner. Self-sustained flame spread also occurred in the test using a PVC membrane over mineral wool insulation. That test was terminated after 11 minutes once fire propagation between sections of the PV array had been confirmed.
The researchers said the findings show that the thermal properties of the material directly beneath a thin PVC membrane can significantly influence flame spread. They concluded that the CPB can reduce the likelihood of self-sustained flame spread by acting as a heat sink and limiting heat transfer between the roofing membrane and EPS insulation.
“The results should therefore be regarded as a basis for further technical discussion and testing, rather than as evidence of a definitive solution or an approved roof configuration,” Gallo said. “More broadly, our findings support assessing the fire safety of rooftop PV at the level of the complete roof-PV system and highlight the need for further testing and harmonized assessment methods.”
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