Find the protection objective behind the material requirement
A requirement may concern the material's fire contribution, the heat effect on combustible insulation or spread into a larger roof area. These objectives are related but not identical. Therefore ask first which performance is to be achieved in the specific project.
The spatial scope also counts: the whole roof area, the PV field, edge strips or individual details result in different quantities and costs. A clearly marked plan prevents bidders from pricing completely different areas.
Why millimetres are not simply equivalent
40 mm of one material and 15 mm of another can have very different thermal properties. Thickness, density, moisture, thermal conductivity and behaviour under fire exposure interact. A smaller thickness can be technically interesting; the comparison, however, requires the same task and matching evidence.
ETA-11/0458, for example, contains equivalent concrete thicknesses for certain concrete elements clad with Aestuver. Annex D relates to the tested cladding of load-bearing concrete slabs or walls. The figures therefore cannot simply stand in as evidence for loose-laid boards above a roof membrane. They can structure a technical discussion but do not replace matching the application. [1]
EI 30 is a different statement from A1
If a thermal barrier with fire resistance is required, naming a non-combustible material class alone is not enough. Conversely, matching construction evidence can provide additional information missing from a simple product data sheet.
Important are fire side, load-bearing or bearing conditions, joints, fixing and the protected layer. The guide to A1, EI and BROOF explains these levels. For an alternative, the required functions are demonstrated as directly as possible.
Build a dossier that enables a decision
Start with the roof section and the PV plan. Next to them, place the required reference build-up and the offered alternative. For each difference, state its possible technical significance and the document that contributes to the assessment.
This includes mass per unit area, weathering, wind, waterproofing, fixing and maintenance. An alternative protective layer can be economically attractive if it solves the same relevant task with less installation effort or less additional load. Such advantages are calculated traceably, not merely asserted.
Record acceptance before installation
Technical equivalence and acceptance in the insurance contract are different decisions. Therefore have the assessment of the specific option recorded with drawing revision and conditions. A positive phone call about a material name is less robust than a decision on the documented build-up.
VdS 3145 and the FRISSBE/ZAG guideline offer technical orientation for the design of PV systems. They replace neither the individual risk decision nor any project assessment required. A shared dossier makes this coordination easier. [2] [3]
Have the specific alternative assessed in writing, including the drawing revision and conditions. Compare the required protection objective, not just material thickness.