Study by Swiss Federal Office of Energy: U-values of walls measured

greenTEG AG: A newly developed device (gSKIN® U-Value Kit) was used to measure the U-values of various wall types built before 1985. The goal was to assess the validity of the embedded U-values in the GEAK (building energy certificate of the Swiss cantons) calculation model for typical walls that are due for a retrofit. The measured U-values of the walls built before the implementation of the first model energy codes (mid-70s) were much lower than the U-value given for this type of wall in the GEAK. These measured U-values appear valid and therefore changes to the GEAK U-values are proposed.

In general, the U-values were scattered over a relatively large range (both within and between different wall types). The measurements showed that the gSKIN® U-Value Kit can provide reasonable in-situ measured U-values with an accuracy of ±20% compared to the calculated values. The approximately 100 measurements also illustrated the limits of the device’s capabilities and the need for an experienced user. Therefore it is recommended that this device be used by experts in the field of U-values. Stable boundary conditions and measurements with two or more U-value kits provide the best results.

The company Hässig Sustech conducted the measurements and wrote the study on behalf of the Swiss Federal Office of Energy. For the U-value measurements, greenTEG’s U-Value Kit was used.