The influence of insulation on the thermal inertia of existing residential building envelopes

The paper discusses internal building envelope retrofitting of multi-storey, multi-owner residential buildings. The main question is how does the additional insulation placed on the inner side of the building envelope affect its thermal inertia. Among other reasons, thermal inertia is important in increasing human comfort in the space, avoiding overheating in summer, and managing solar gains. Inside insulation can alter this behaviour, and the aim is to understand the positive and negative consequences of such an intervention. The work assesses insulating materials and components integrated in the internal side of the retrofitted buildings in the summer periods. The scope of work addresses warm temperate climate with dry and warm summers, abbreviated as ‘Csb’ according to Koppen climate classification, and which is represented in the city of Milan, Italy. The alternatives assessed consider lightweight as well as massive building envelopes. To that aim, simulations are carried out in order to understand the variance in the thermal behaviour of the envelope, corresponding to the change in insulation placement on the building envelope (inside, outside or without). Analytical assessment is performed in order to include air and surface temperatures and internal heat loads. The results show that, under the conditions of this study, both internal and external insulation are beneficial in terms of surface, indoor air and operative temperatures in summertime. With insulation placed outside, the higher thermal capacity increases instead the comfort conditions, measured in discomfort degree hours (DDH).