The influence of internal insulation on the thermal inertia of existing residential building envelopes in hot arid climates

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. The scope of work addresses hot arid climates, abbreviated as ‘BWh’ according to Koppen climate classification, and which is represented in the city of Cairo, Egypt. The building envelope alternatives assessed consider light as well as massive building envelopes. To that aim, simulations are carried out in order to understand the variance in the thermal behavior of the envelope, corresponding to the change in insulation position on the existing one (inside, outside or without). Analytical assessment is performed in order to include air and surface temperatures and building cooling loads. The results show that, under the conditions of this study, both internal and external insulation are beneficial in terms of surface and indoor air temperatures in summertime. With insulation placed outside, the higher thermal capacity on the inner surface increases the comfort conditions, measured in discomfort degree hours (DDH).