Air leakages in a retrofitted building from 1930: measurements and numerical simulations

Many buildings in Sweden are in need of renovation in order to meet the current standards of energy use in buildings. Particularly challenging are old listed buildings, the majority built before 1950, because the renovation is restricted to the parts that do not change the appearance of the building. This paper presents experiences gained during the renovation of a listed building where aging of materials, movements and settlements during the building operation have left trails in form of air leakage paths that are difficult to cover by renovation. The aim of the work is to bring up certain issues related to air movements in old houses that are not necessarily present in new ones. In the renovation project in question, efforts were made to seal the exterior walls with polyethylene foil before additional insulation in form of vacuum insulating panels was installed. The blower door tests taken in the apartments showed that the air permeability of the building remained basically unchanged after the retrofit. Complementary diagnostics with thermal imaging camera revealed that air leakage paths in intermediate floors and interior walls substantially contributed to the overall air leakage of the building. It was then concluded that the blower door tests alone were not sufficient for the estimation of the air permeability of the building. In addition, hygrothermal measurements in exterior walls showed that new air leakage paths were created between the old wall and the additional insulation. By using numerical simulations, it has been proven that it is the outdoor air that flows through these new air paths, which is advantageous from the moisture safety point of view. However, the flow of outdoor air through the exterior wall increases the overall thermal transmittance of the wall and thus decreases the effects of additional insulation.