Ein Luxemburger Leitfaden für die Planung von Innendämmprojekten durch Messungen und Simulationen

A Luxembourg guide for planning interior insulation projects using measurements and simulations

The decarbonisation of the building sector plays a crucial role on the path to climate neutrality. To this end, the current EU directives are constantly being implemented in Luxembourg and for some years now, a minimum heat transmission coefficient U to be achieved for renovations has also been included in the Luxembourg Building Energy Act. Especially in historic and protected buildings, but also in many other buildings with limited space on the outside for example, interior insulation is often the only way to reduce transmission heat losses through the façade and thus also reduce greenhouse gas emissions. Limit values to be complied with are also specified for this type of insulation measure. At the same time, however, many architects and engineers are concerned that the use of interior insulation will risk structural damage and thus damage the building fabric or promote an unhealthy indoor climate. This is often due to the “dew point shift” in the masonry as a result of the interior insulation. This probably arises from the simplifications of the “Glaser”-method that is internalized by many planners, although in practice very often no permanent wetting occurs and no mold grows due to the sorption properties and capillarity of correctly chosen insulation material. As a result, the internal insulation works more often than expected without any problems. This article clarifies whether and by which building physics measurements and simulations in the preparation phase of an internal insulation project planning reliability can be increased. One focus is on hygrothermal functional verification for natural stone façades, where the standard-based, simplified verification procedure usually fails because conservative assumptions are deposited or the standards even excludes this application to stay on the save side. At the University of Luxembourg, a general guideline for interior insulation projects has been developed on behalf of the Public Buildings' Administration (Administration des Bâtiments Publics - ABP for short) in order to provide planning aid to architects and engineers. This guideline is summarised hereafter.