What should you check before using a hygrothermal calculation in a design?

Record every layer thickness and distinguish confirmed data from estimates. “380 mm brickwork” may be too vague where voids, repairs or different mortars occur. Flag an unknown layer for investigation instead of assigning it a favourable library value.

Use climate data suited to the site and calculation method. A single coldest day cannot replace monthly conditions if the program expects a monthly series. Document outdoor conditions in the report too.

Enter layers in their actual order from inside to outside. The position of a vapour-retarding facing matters for moisture assessment. For a composite board, represent the PIR, facing and gypsum layer according to the selected system model instead of substituting an arbitrary single material.

Check units: 80 mm is 0.08 m, not 0.8 m. Distinguish the vapour diffusion resistance factor μ from the equivalent air layer thickness sd. An input error may not be obvious on the final graph. Thermal and vapour data must describe the same board variant.

The U-value describes heat transfer through the modelled wall. A low figure does not prove that all layers will stay dry. Report the internal surface temperature separately from the assessment of condensation inside the assembly, especially for internal insulation.

The method in PN-EN ISO 13788 is simplified. It does not fully represent liquid water transport, airflow through gaps or moisture storage effects. For masonry wetted by driving rain or containing damp beam ends, the designer should consider a more detailed analysis with suitable material data.

Compare at least two realistic operating scenarios. For example, model a room at 20°C and 45% relative humidity, then at the same temperature and 60%. These are comparison assumptions, not universal humidity targets. Identify the surfaces and months that become critical.

Test the effect of uncertain thermal conductivity in old masonry. If a small change reverses the assessment, the margin is narrow. Investigate the wall further or revise the build-up. More internal insulation can improve the U-value while lowering the temperature of the original masonry.

A one-dimensional section misses ring beams, corners, slab edges and window junctions. Mark these on plans and sections. Thermal bridges may require two- or three-dimensional calculations. A corner surface can be colder than the wall centre shown by the calculator.

Assess airtightness as well. An unsealed cable penetration can carry humid air behind the insulation despite a satisfactory diffusion calculation. Design buildable perimeter seals, reveals and service penetrations that can be inspected before concealment.

Record the layers, inputs, boundary conditions, method and design revision. List exclusions such as separately assessed thermal bridges or omitted fixings. A green pass indicator alone cannot explain why the design was accepted.

Include detail drawings and requirements for the installer. If the result depends on a dry substrate or a sealed perimeter, specify it in the works description. Different facings, adhesive, fixings or ventilation may require reassessment. At handover compare the installed build-up with the documented variant, not just its insulation thickness.