Choosing EPS, XPS or PIR when renovating a house

Each group contains different products. Façade boards, floor boards and those intended for moisture contact can have different properties. Neither colour nor a generic material name settles the choice. You need the exact variant’s designation and documentation.

In an old house, floor height, reveal width or water near the foundation may be the main constraint. Record that before comparing conductivity. If a material cannot cope with the expected moisture or loading, its thermal performance is no help. Also check that the substrate permits the system’s specified fixing method.

Lower conductivity gives the same layer resistance at a smaller thickness. In an example with R = 4.00 m²K/W, a material with λ 0.036 needs 144 mm; λ 0.034 needs 136 mm; and λ 0.022 needs 88 mm. These are theoretical calculations using the stated values, not a selection of actual products.

Use actual declarations and available thicknesses in the design. Fleece-faced PIR for rendering may have different conductivity from aluminium-faced PIR. The resistance of the complete element includes existing layers too. Centimetres saved are therefore not a fixed percentage attached to a material name.

Selected XPS grades are used in assemblies exposed to moisture and higher loads. Special EPS variants also exist for specific applications. Do not extend that suitability to every board in either group. Low water absorption does not make insulation a substitute for waterproofing.

For loading, long-term conditions and concentrated pressures matter. CS(10) describes a test at 10% deformation, not permissible service pressure over many years. Beneath heavy fixtures, terrace supports or vehicle wheels, check the full floor assembly and force distribution.

A gas-tight aluminium laminate on PIR affects water-vapour movement, particularly with internal insulation. A board without that facing may behave differently despite a similar core. Vapour-control layers should follow an assessment of the element, not an assumption that more membrane always helps.

Read reaction-to-fire classifications for the specific product. Fire resistance, in contrast, applies to a defined assembly. It cannot be attributed to an entire house from the foam type. On façades, system classification matters; for roofs, performance under external fire exposure matters too.

PIR can help where a thinner build-up avoids alterations to thresholds or flashings. EPS may be considered for large areas where sufficient thickness fits and the system is compatible. XPS may suit different moisture conditions. Final cost depends on the chosen variant and associated work.

Include substrate preparation, fixings, waterproofing, finishes and waste. Check how local damage can be repaired. Do not automatically claim an environmental advantage for a material. A comparison needs consistent data for the complete solution, its durability and the assumed thermal performance.

For phased renovations, retain documentation for every product variant used. Apparently similar boards may have different compression or moisture properties. At the next stage, the product designation will help more than a photograph of its colour.