Moisture Robustness During Retrofitting of Timber Frame Walls with Vacuum Insulation Panels: Experimental and Theoretical Studies

Abstract

AbstractA large amount of the buildings in Norway is from the 1960s–1980s. Many of these buildings have timber frame walls and are now ready for retrofitting. Application of vacuum insulation panels (VIPs) may make it easier to improve the thermal insulation in timber frame walls with a minimal additional thickness. Retrofitting of timber frame walls using VIPs may therefore be performed without large changes to the building, e.g. extension of the roof protruding and fitting of windows. Additionally, U-values low enough to fulfil passive house standards or zero energy building requirements may be achieved, thus contributing to a reduction of the energy use and CO2 emissions within the building sector. This work investigates different ways of retrofitting timber frame walls with VIPs on the exterior or the interior side. Timber frame walls retrofitted with VIPs on the exterior side is interesting because it allows for a continuous layer of VIPs over the building envelope, and it is also considered as a more robust solution than VIPs at the interior side (less risk of puncture). However, application of VIPs on the exterior side may cause condensation in the wall. To investigate this, a wall module containing four different wall fields was built between two climate rooms with indoor and outdoor climate, respectively. One field represents a reference wall built according to Norwegian building regulations from the 1970s. The three other fields represent different ways of improving the thermal insulation of the reference field, with VIPs at the interior or the exterior side. To minimize the size of the thermal bridge caused by traditional methods of fastening VIPs, a tailor-made VIP fastening bracket was applied in the build-up of the fields. Temperature, relative humidity (RH), and surface wetness was measured during the experiment. The surface wetness was measured on the wind barrier with a tailor-made surface wetness sensor consisting of double-sided tape, metal electrodes and paper sheets. In addition to the experimental investigations, numerical simulations and condensation control calculations were performed for the same wall fields with hygrothermal robustness performance as the main objective. In overall, the results from the experiments, simulations, and condensation controls conclude that timber frame buildings insulated with 100 mm mineral wool, might be retrofitted at the outside by adding 30 mm VIPs. However, this method for retrofitting provide limits to outdoor temperature, indoor moisture excess and indoor temperature.KeywordsThermal insulationRetrofittingTimber frame wallVacuum insulation panelVIPMoistureRobustness