Feasibility of exterior air barriers in timber frame construction

Abstract

The primary objective of the present work is assessing the feasibility of exterior air barrier systems in highly insulated timber frame construction. The first part of this thesis presents in situ and laboratory measurements that verify whether acceptable airtightness levels can be achieved through improving the continuity of the wind barrier. These investigations quantify typical air leakage paths in such systems and, further, shed light on the practical aspects of its execution. The second part of the study examines the hygrothermal behaviour of lightweight elements with an exterior air barrier. This aspect covers both experimental and numerical work and is restricted to wall elements only. A new vertical hotbox/coldbox test setup was applied to simulate the hygrothermal performance of full-scale walls under controlled climate conditions. In addition to these measurements, the study examined the onset of interstitial condensation on hygroscopic and/or capillary active air barrier materials on smaller test specimens. The thesis at hand will further outline a numerical modelling strategy to assess the heat, air and moisture (HAM) transport in lightweight walls. Herein, strong emphasis lies in the evaluation of the presented modelling approach with a combination of benchmarks from the literature and the experimental data obtained in this work. Finally, annual numerical simulations assessing the hygrothermal performance of exterior air barriers in cold and moderate climates will be presented. A parameter study will examine the (1) behaviour of various wall assemblies, (2) identify the impact of bad workmanship and (3) illustrate its behaviour in several European climates.