Hygrothermal Performance of Highly Insulated Timber-frame External Wall

Abstract

The nearly zero energy buildings (nZEB) ideology foresees first and foremost that heat losses should be reduced remarkably compared to the present levels. The European Union has adopted an ambitious vision for the energy efficiency of its buildings and by the end of 2020 all new buildings must meet nZEB requirements. The efficient way to meet these requirements is to design and build passive, nZEB, highly insulated buildings.This paper presents the outcomes of analysis of the hygrothermal performance of the highly insulated building envelope of the detached house, built in Estonia. The results indicated that the dry-out period of constructional moisture is directly dependent on initial moisture content of materials in structure and a higher risk was detected if vapor permeability of outer layers in the envelope is low. Also critical aspects of moisture performance change due to the modifications of designed materials in construction process without preliminary analysis are described. Thermal resistance of the wind barrier and water vapor permeability of the vapor barrier, also moisture capacity of insulation layer had the strongest influence on the relative humidity and hence, to mould growth risk in the critical point of highly insulated timber-frame external wall, between the insulation and the wind barrier surface.In the design of highly insulated timber-frame walls more attention should be paid to the hygrothermal performance and moisture safety analysis. As a result of this study, some of the functional solutions of timber-frame external walls are described in this paper.