How to choose sandwich panels for insulation, moisture and structural loads

For a refurbishment, establish whether the use is changing. Converting a warehouse into a workshop may change the insulation and ventilation requirements. Settle this before ordering panels. Adding insulation later creates a different assembly that needs to be assessed again.

For a project in Poland, establish the legal basis for using the earlier Polish technical conditions for buildings (WT). Following the 2026 changes, temporary provisions allow the earlier rules to be applied in specified circumstances for 18 months from 20 September 2026. Confirm the procedure and formalities for the particular project; refurbishments do not all follow the same route.

Under those earlier Polish rules, for a design indoor temperature of at least 16 °C, the maximum corrected thermal transmittance (Uc) is 0.20 W/(m²·K) for external walls and 0.15 W/(m²·K) for roofs. Use these limits if they form the basis of the project. Other operating conditions can lead to different limits.

These limits do not prescribe a single thickness of PIR, EPS or mineral wool. Use the data for the specific panel and assess the installed envelope. A wall with windows, large doors and structural connections performs differently from an uninterrupted area of panel.

PN-EN 14509 covers factory-made, self-supporting sandwich panels with metal facings on both sides. It provides a basis for determining and declaring their properties. It neither replaces the structural design of the building nor specifies a universal thickness for walls and roofs.

Check the exact core, facing thickness, profile and joint. Product data must match the delivered configuration. A PIR insulation board with a thin laminate facing, or a panel with laminate on one side, does not automatically share the properties of a sandwich panel with steel on both sides.

PN-EN ISO 13788 describes simplified methods for assessing surface temperature and condensation within a construction. The result depends on the assumed temperature, humidity and layer build-up. The methods do not account for every process, including airflow through gaps or the full movement of water within a material.

Examine joints, flashings and service penetrations. A low U-value does not rule out condensation at a poorly formed junction. Humid rooms and cold stores merit particular attention. The seal must suit the direction of vapour movement and the operating conditions in that building.

Core thickness affects structural behaviour, but so do the facings, span lengths, support widths, span arrangement and loading. A load table for another profile or metal thickness is not a substitute. Assess snow, wind, self-weight and equipment loads for the actual design.

On roofs, equipment and maintenance traffic can impose local loads. Fixings must transfer the forces to the appropriate supporting structure. PIR thickness alone cannot establish whether a roof can be walked on. A thicker panel will not remedy a corroded or misaligned support either.

Select a configuration that simultaneously meets thermal, structural, fire and operational requirements. Specify thickness, facings, coatings, lengths and installation conditions. The fire classification must cover the actual assembly. If the core or supports change, check whether the classification still applies.

Finally compare the price of the complete envelope, including supports and junction details. A thicker panel may simplify a detail, or the limiting factor may still be a support or joint. The selection is complete only when the same configuration passes every applicable check.

For each item, record who will confirm compliance: the designer, the supplier or the installer at acceptance. This identifies gaps in the documentation and helps catch substitutions that improve one characteristic but invalidate the assumptions behind another check.