Evaluation of the criticality of thermal bridges

Abstract

Thermal bridges can be an important reason for the renovation of old apartment buildings. This study presents a method for the critical analysis of thermal bridges. The risk of failure, i.e., surface condensation or mould growth, is evaluated by using the temperature factor fRsi.load based on indoor hygrothermal loads and the temperature factor fRsi.resistance from thermography measurements. The proposed method is employed for two practical applications—a case study analysis of the entire Estonian apartment building stock and a case study concerning the thermal bridges before and after the renovation of a precast concrete large-panel apartment building. The results show that critical thermal bridges caused by low surface temperature exist in all types of apartment buildings. The measured temperature factors were as low as fRsi.res < 0.65 for several junctions in concrete buildings and for the external wall/window junctions of brick buildings. The temperature factors from indoor hygrothermal loads are as high as fRsi.load = 0.99 for the worst dwelling unit and fRsi.load = 0.80 at a 90% reliability level for mould growth in concrete buildings. The calculated risk for surface condensation is 45–51% and for mould growth is 45–54%; this is highest in concrete buildings for both criteria. The calculated results are confirmed by visually detected mould growth, which ranges between 28 and 46% depending on the type of building. The proposed method can be used in stochastic analysis if the present need for renovation or designed renovation alternatives is under consideration.