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 f Rsi.load based on indoor hygrothermal loads and the temperature factor f Rsi.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 f Rsi.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 f Rsi.load = 0.99 for the worst dwelling unit and f Rsi.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.