TEP ROOF OY · MATERIAL AND INSTALLATION GUIDE
PIR insulation on low-slope roofs
PIR is a rigid thermal insulation whose low thermal conductivity can reduce the required build-up thickness. Select the insulation facing and the waterproofing above it as a compatible combination.
Where can PIR be useful?
- Consider comparing a PIR option where the available height at eaves, upstands or roof equipment junctions is limited. Use the same whole-roof U-value target for the comparison; board thickness alone does not establish equivalent performance.
- Products have different facings, edge profiles and intended uses. A bitumen-faced roof board, an aluminium-faced board and another multilayer-faced board do not provide the same waterproofing substrate. Specify the exact product and roof layers in the quotation.
Waterproofing substrate and fire documentation
- Options may include a mineral wool cover layer above PIR or a PIR surface approved for direct installation of the selected roof covering. Direct installation, torching, bonding and mechanical fixing are not freely interchangeable methods.
- Request classification documents for the exact insulation and roofing combination, together with the necessary protection and fixing details. The product's reaction-to-fire class, the roof covering's BROOF(t2) classification and the roof assembly's fire resistance are different things. Selecting PIR alone does not confirm any of them.
Specify vapour control separately
- An impermeable facing alone does not make the whole roof assembly vapour-tight. For example, a manufacturer's concrete-deck build-up with PIR and a mineral wool cover layer includes a separate vapour control layer beneath the insulation. Selection depends on the whole build-up and the internal moisture load.
- If the insulation layer is also intended to act as a vapour control layer, a demonstrated solution is needed for board joints, edges, penetrations and layer position. Do not apply joint-foaming or taping instructions from another application directly to a low-slope roof build-up.
Check before covering
- Verify the substrate's load-bearing capacity and evenness, board orientation, edge joints, staggering of joints and fixings. Check how equipment loads are distributed through the entire insulation combination. Follow the specific system instructions and project fixing design.
- Protect insulation and unfinished layers from the weather. PIR's low water absorption does not make joints or the temporary roof watertight. Check the vapour control layer, damaged facings, junctions and temporary weather seals at work breaks.
Use and design responsibility
TEP Roof Oy guide cards support project preparation and the definition of contract scope. They are not project-specific construction designs. The project structural designer is always responsible for checking the suitability of the solutions presented and adapting them to the project's structures, loads and requirements. Construction requires project-specific design and approval, together with the current manufacturer's instructions for the selected products.
Sources
An editorial compilation by TEP Roof Oy. The product- and system-specific source instructions must be checked for the selected solution.
- Finnfoam Oy: FF-PIR roof boards and technical data: products, 1 January 2026, pp. 10-13 Checked 19.10.2026
- Recticel Insulation: Eurothane Silver E FR: low-slope roof insulation and system-specific classifications Checked 19.10.2026
- Recticel Insulation: YP002-0: PIR roof on a concrete deck with a mineral wool cover layer, vapour control layer and installation Checked 19.10.2026