The importance of thermal bridge correction in energy refurbishment of existing buildings

The aim of the present paper is to determinate the optimal correction of thermal bridges in buildings refurbishment, taking into account the minimum insulation requirements provided by Italian legislation. The Decree 26.06.2015, transposing the directive 2010/31/EU, imposes the respect of limit values of the mean thermal transmittance of building components and of the mean global heat transmission coefficient of entire façades. Both such parameters include thermal bridges contribution. A 30% derogation on mean thermal transmittance limit values is allowed in case of filling wall cavities of buildings, object of simple energy refurbishment, with insulating materials. A case study, concerning a building façade repetitive module with door window, balcony and roller shutter box, is considered; in addition to junctions due to beams and pillars, the thermal bridges due to lintel, threshold, jambs and balcony are examined. An aerogel insulating material is used for their correction. The linear thermal transmittance is determined by a 2-D numerical model. Results show that it is very difficult to respect the limit values for the mean thermal transmittance; it is possible to comply the limit values for mean global heat transmission coefficient using high performance windows.