Interior insulation retrofit of a historical brick wall using vacuum insulation panels: Hygrothermal numerical simulations and laboratory investigations

Old listed buildings need to be retrofitted to reduce the energy use for heating. The possible thickness of the insulation layer is limited by the existing construction. Vacuum insulation panels (VIPs) require less thickness than conventional insulation materials to reach the same thermal resistance. Therefore, it could be more appropriate to use VIPs than conventional insulation materials when retrofitting the building envelope of listed buildings. The aim of this study is to investigate the hygrothermal performance of a brick wall with wooden beam ends after it was insulated on the interior with VIPs. One- and two-dimensional hygrothermal numerical simulations were used to design a laboratory study in a large-scale building envelope climate simulator. The wall was exposed to driving rain on the exterior surface and a temperature gradient. The relative humidity in the wall increased substantially when exposed to driving rain. The moisture content in the wooden beams also increased. There was no significant difference between the relative humidity in the wooden beam ends for the cases with and without VIPs. However, it was found that the reduced temperature in the brick after the VIPs were added led to a higher relative humidity in the wooden beams. It was also clear that when VIPs were added to the interior, the drying capacity to that side of the wall was substantially reduced. Finally, calculations of the U-value showed a large potential to reduce the energy use using VIPs on the interior of brick walls.