Hygrothermal performance of AAC exterior wall after additional insulation with prefabricated elements in Estonia.

The nearly zero energy buildings (nZEB) ideology requires foremost that the heat losses of buildings should be reduced significantly in the coming decades compared to the present levels. The efficient way to meet these requirements is to renovate apartment or public buildings with prefabricated timber frame insulation elements for the major renovation. The current study observes the hygrothermal performance of an external envelope of a 3-storey apartment building, built in Estonia of large panels of aerated autoclaved concrete (AAC) and insulated in the process of deep energy renovation with prefabricated modular elements. Long-term hygrothermal measurements were taken in the different critical spots of the external envelope and a series of combinations with modular elements were analyzed, using building performance simulation software to compare risks and the main hygrothermal properties. The analysis indicated that thermal resistance and water vapor permeability of the wind barrier layer and the presence or absence of the vapor control layer had the strongest influence on the moisture content and drying (and therefore the risk of mold growth risk) at the critical points (between the insulation layer and the wind barrier surface, and between the existing AAC wall surface and the vapor control layer) of the additional insulated exterior wall. [ABSTRACT FROM AUTHOR]