AllShield BarrierSheet Approved for FM 4478 PV roof assemblies

AllShield BarrierSheet is FM Approved for FM 4478 PV roof assemblies. The non-combustible mineral cover board delivers proven downward fire protection, supporting fire-safe and insurable photovoltaic roofs worldwide.

A proven FM Approved pathway for fire-safe and insurable solar roofs

Photovoltaic installations fundamentally change the fire behaviour of flat roofs. Heat accumulation beneath PV modules, prolonged downward fire exposure and interaction with combustible insulation layers introduce risks that are not present in conventional non-PV roofs.

FM 4478 is the dedicated FM Approvals standard developed to address these risks. It is the global reference for evaluating fire performance of complete roof assemblies with photovoltaic systems.

AllShield BarrierSheet is FM Approved and officially listed in RoofNav for use in FM 4478 PV roof assemblies. This confirms that BarrierSheet has a defined, tested and approved role within roof systems that meet FM 4478 requirements for PV installations.

AllShield provides multiple FM Approved solutions for photovoltaic roofs. BarrierSheet is the solution approved for FM 4478 PV roof assemblies, while other AllShield solutions address different FM standards and roof conditions.

FM 4478 approval is always granted to the complete roof assembly. Final acceptance remains subject to the assessment of the insurer’s risk engineer.

FM 4478 explained

FM 4478, Approval Standard for PV roof assemblies, was introduced because traditional roofing standards do not sufficiently address the fire behaviour created by photovoltaic systems.

The standard evaluates complete roof assemblies under realistic PV fire exposure and environmental loading, including:

• External and internal fire resistance.

• Absence of rapid flame spread and burn-through.

• No flaming debris.

• Downward fire behaviour influenced by PV modules.

• Interaction between modules, frames and electrical components.

• Heat accumulation and cavity fire development beneath panels.

• Wind uplift and storm resistance with PV installed.

• Mechanical resistance including hail.

Only roof assemblies that pass the full test sequence are listed in RoofNav as FM Approved Class 1 roofs with PV.

Why FM 4478 matters to insurers

PV roofs introduce ignition mechanisms and downward fire paths that are not covered by non-PV roofing standards.

For insurers and risk engineers, FM 4478 provides:

• A clear, globally recognised benchmark for PV roof fire performance.

• Independent verification of predictable and controlled fire behaviour.

• Confidence that a roof system performs as tested under severe conditions.

FM 4478 Class 1 roofs with PV
→ recognised as low-risk and insurable.

PV roofs without FM 4478
→ frequently restricted, excluded or rejected.

The function of AllShield BarrierSheet within an FM 4478 roof assembly

Within an FM 4478 Approved PV roof assembly, AllShield BarrierSheet functions as a non-combustible mineral fire barrier layer positioned directly beneath the roof membrane and photovoltaic system.

Its primary function is to interrupt downward fire propagation originating from PV modules and roof membranes during a fire event. By introducing a stable, non-combustible layer at this critical interface, BarrierSheet prevents direct flame penetration into underlying combustible insulation layers such as PIR and EPS.

In FM 4478 fire scenarios, where prolonged heat exposure and cavity fire development beneath PV modules are dominant risk factors, the BarrierSheet layer provides:

• A physical fire break between the ignition source and the insulation.

• Thermal buffering that reduces peak temperatures in lower roof layers.

• Structural stability of the roof assembly during sustained fire exposure.

By performing this defined function, BarrierSheet enables the overall roof assembly to meet FM 4478 performance requirements when combined with FM Approved membranes, insulation and fastening systems.

FM 4478 approval applies to the complete roof assembly. BarrierSheet’s role within that assembly is to deliver predictable and repeatable downward fire protection as part of the tested system.

Independent testing and long-term confidence

Beyond FM Approvals, the performance of AllShield BarrierSheet is supported by extensive independent testing in Europe.

Large-scale PV fire testing at ZAG, Slovenia

Independent large-scale testing under severe PV fire scenarios demonstrated:

• No direct fire penetration below the BarrierSheet layer.

• Effective protection of EPS, PIR and mixed insulation systems.

• Stable behaviour of the roof assembly under sustained thermal loading.

Dutch PV roofing standard testing

Testing performed by Kiwa-BDA under the Dutch roofing standard for PV systems, still under development, confirmed:

• Controlled fire development beneath PV modules.

• No ignition of underlying insulation layers.

• Downward fire performance consistent with FM-tested assemblies.

European classification

• Efectis: BROOF(t1), the highest European classification for external fire exposure.

Together, these results reinforce that BarrierSheet delivers durable downward fire protection across both FM and European regulatory frameworks.

Upgrading existing roofs for PV

AllShield BarrierSheet enables existing roofs to be upgraded to systems suitable for photovoltaic installation, provided the complete roof build-up meets FM requirements.

Typical applications include:

• Retrofit projects where full roof replacement is undesirable.

• Roofs with limited load capacity requiring a lightweight fire barrier.

• Projects requiring a dry, mechanically installed solution.

As with all FM Approved systems, final acceptance depends on the complete roof assembly and the insurer’s risk engineer.

AllShield BarrierSheet FM status

• FM 4470 Approved for non-PV roof assemblies.

• FM Approved and listed in RoofNav for use in FM 4478 PV roof assemblies.

This status confirms ongoing compliance with FM Approvals requirements and continued surveillance audits.

What this means in practice

For building owners

• Proven downward fire protection beneath PV installations.

• International recognition through FM Approvals and RoofNav.

• Long-term insurability when accepted by the insurer’s risk engineer.

For insurers and brokers

• Clear reference to FM 4478 Approved PV roof assemblies.

• Reduced uncertainty in PV roof risk assessment.

• Faster and more consistent underwriting decisions.

Ask your insurance engineer to assess whether your roof can be made fire-safe with FM 4478 Approved BarrierSheets in a way that will allow insurance coverage when adding PV.