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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.

In this study, indoor air humidity and temperature levels have been measured in 117 houses in Trondheim, Norway. The houses were randomly selected for each of the following types: detached one-family houses, semidetached two-family houses, row houses, and apartment buildings. The temperature and relative humidity (RH) were measured at 15-min interval over a period of 1 week. The measurements were made in bedrooms, living rooms, bathrooms, and outdoors. The internal moisture excess, which is the difference between indoor and outdoor air water vapour content, was calculated. The dataset was analysed in regard to average values of internal moisture excess and its dependency of outdoor climate. The daily variations of indoor RH, temperature, and internal moisture excess for the various types of rooms were also analysed. The typical diurnal variations of RH, temperature, and internal moisture excess are presented together with the statistical variation. The effect of influencing factors such as occupancy (area per person), type of basic ventilation of the house, type of building, time of the year, and the level of average indoor air humidity was investigated.To get a deeper understanding of some of the factors influencing the diurnal variations of the indoor air humidity observed in the field measurements, computer simulations of the indoor air humidity were also performed. The simulations were made using the numerical software WUFI Plus.

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