Internal insulation of masonry walls may significantly increase the decay risk of embedded wooden beams due to lower temperature and consequently lower drying potential in retrofitted existing walls. Since high moisture contents will affect performance and service life of wood, the assessment of moisture-related damage risks in wooden beam-ends in internally insulated masonry walls is particularly relevant to heritage buildings. The proper selection of indoor and outdoor materials and the addition of an embedded heating source offer means of decreasing this risk. Numerical studies of hygrothermal performance of wooden beam-ends support risk assessment but traditionally this has been performed with 2D models. Therefore, in order to assess whether a 2D numerical model can represent accurately the 3D hygrothermal behavior of wooden beam-ends, the difference between 2D and 3D model results of the hygrothermal performance of wooden beam-ends embedded in internally insulated masonry wall is analysed for a northern continental climate. Given the small differences in relative humidity, temperature and mould index between the 2D and 3D models, it is suitable to replace 3D models with 2D ones for predicting the risk of moisture-related problems in the wood beam-end when studying the impact of different envelope components. However, for evaluating the effect of active heating on wooden beam-end performance, it is found that a 3D hygrothermal model should be used. In this case, a 2D model cannot accurately model heating locally at the beam-end resulting in an over prediction of temperature and thus in an underprediction of the moisture damage risk.

۱٫ Introduction

Many historical buildings are built with solid brick walls and wooden beam constructions. These buildings are, for the most part, not energy efficient and represent a significant energy-saving potential. For historical buildings with a worth-preserving facade, the only possible energy retrofit measure possible given their heritage value is internal wall insulation. It is possible to reduce the heating energy consumption in the historical buildings by 30–۴۰% by retrofitting the existing walls with internal insulation [1]. However, adding insulation to masonry walls from the indoor side may significantly increase moisture-related damage risks to the building materials and components that are exposed to lower temperature and consequently lower drying potential in the existing wall [2–۱۰]. As the floors in old masonry buildings are often carried by wooden beams embedded in the brick masonry, moisture-related problems in wooden beam-ends in internally insulated masonry walls is of high practical importance [11] and should be correctly evaluated [12].