PIR is a rigid foam used as insulation. The suitability of a PIR board depends on the particular product and the complete roof assembly.
What does this mean on your roof?
The material name alone does not establish thickness, facing or intended application. Products may have different properties and uses.
Request the exact board specification and its declared rating. Also assess how insulation connects at edges, penetrations and retained components, rather than comparing only uninterrupted areas of new material.
On a flat roof, new insulation can affect height available for upstands and drainage. On a pitched roof, space and connections with existing layers matter. Choosing solely on thinness or thickness leaves those consequences out of the comparison. Record which components will be adjusted and how proposed product changes during execution will be assessed before one material is substituted for another.
Frequently asked questions
Is PIR always the best roof insulation?
No. Suitability depends on construction, space, application and project requirements.
Is the material name enough in a quotation?
No. Product, thickness and the coordinated roof assembly need to be clear.
Consulted 19 September 2026. Check requirements for your own address and selected system.