Tightening against rain and wind for facades – practical experiences

SINTEF Building and Infrastructure's archive of building defect assignments represents one of Norway's most important sources of knowledge on types of process induced building defects and related causes. This knowledge has been thoroughly analysed during the last years. At least 75 % of these defects are related to moisture, and most of the defects are related to moisture from outside the building (for instance wind-driven rain). Earlier, most building defects were related to roofs. However, an analysis of building defects from 1993 to 2002 reveals that the majority of the defects in this period is related to walls and facades. About 30 % of the defects are related to walls, while about 25 % of the building defects are related to roofs. In 1997 the thermal insulation requirements were restricted. The U-value requirement for walls was set to 0.22 W/m2K. In 2007 new requirement levels were introduced. 0.18 W/m2K was the new requirement for walls. For roofs the U-value was restricted from 0.15 to 0.13 W/m2K. The thermal performance requirement was also restricted for most of the other building sections. The result is a building envelope with more thermal insulation and less transmission heat losses. As a result, outer part of walls on the average has a lower temperature. This leads to reduced drying of built-in moisture and moisture penetrated into the construction from outside. New constructions are therefore more dependent on correct workmanship and solutions built according to sound building physical principals. Using a two-stage tightening to prevent rain water from entering the construction has been an important principle in Norway for more than 50 years. However, one-stage tightening wall systems are often used. Analyses of the archive of building defects show that these systems are vulnerable considering external moisture often due to insufficient workmanship. This paper presents the results of these analyses with focus on examples showing typical weak points like detailing around openings and in the boundary between materials or construction parts. Alternative solutions which have proved to be more reliable are also presented.