What are the hygrothermal consequences of applying exterior air barriers in timber frame construction in Europe?

Abstract

Moisture-induced damage is one of the major causes of degradations and reduced thermal performance in wood frame buildings. It is therefore crucial to incorporate the hygrothermal assessment of new timber frame building envelopes systems from the early development phase onwards. The article at hand presents the simulation results studying the hygrothermal performance of various timber frame wall configurations with exterior air barrier systems. A parameter analysis explores the impact of different European climates, insulation materials, exterior air barrier materials and verifies in addition to the impact of bad workmanship in the installation of the insulation layer. This study reveals that the application of mineral wool (MW) insulated timber frame walls in combination with exterior air barriers results in increased moisture loads. Moreover, small air gap channels between the MW and the adjacent exterior air barrier significantly increase natural convection and add up to harmful moisture levels. Yet the simulations indicate that the use of blown-in cellulose insulation can avoid these issues. The study further indicates that the technique of exterior air barrier is more suitable for continental climates rather than for moderate sea climates in Europe.