Energy refurbishment in existing buildings: thermal bridge correction according to DM 26/06/2015 limit values

The recent Italian decree 26.06.2015, concerning minimum requirements of new and renewed buildings, allows a 30% derogation on mean thermal transmittance limit values in case of insufflation with insulating materials in cavity walls in buildings object of refurbishment. The purpose of the present paper is to study the thermal bridges optimal correction in order to verify the respect of the mean thermal transmittance mandatory values. A typical repetitive module of a building façade with windows, sub windows and rolling shutter boxes is analysed. Thermal bridges due to pillars, beams, lintels, thresholds, jambs and thickness reductions of walls situated under windows are considered. The thermal bridges correction is obtained by means of high performance insulating material layers on the outer side of thermal bridges. A 2-D numerical model is used to determine the linear thermal transmittance of junctions. Calculations carried out by the authors show that the limit values of thermal transmittance provided by the decree are too severe to be respected, even in case of derogation.