Mohammed Ali, AsmaaFarouk, AkramEzzeldin, Mohamed2023-04-042023-04-042022Faculty of Engineeringhttp://repository.msa.edu.eg/xmlui/handle/123456789/5462The usage of energy is one of the most critical challenges in modern life. The majority of the energy we use comes from fossil fuels which cause significant environmental degradation. One of the most effective ways of reducing energy use is using thermal insulation in building exterior walls but at a higher cost. Accordingly, this study discusses selecting the optimal thermal insulation and its thickness to increase building efficiency. The optimum insulation thickness is the thickness of insulating material that saves the most energy while costing the least. In this study, optimum insulation thicknesses of four cities from different regions of Egypt have been calculated for external walls using electricity as energy source. The calculations are made on 5 different traditional insulation materials and 2 nano insulation materials. Different cases have been considered: buildings cooled only, and both heated and cooled. It was found that Glass wool (GW) is the optimal insulation in all given locations, but its optimal thickness is very large and that will reduce the available used spaces which will reduce the rental income of buildings and reduce life cycle cost saving of building. Wherefore this study discusses also selecting the optimal thermal insulation and its thickness in the case of accounting for the impacts of space savings in life cycle saving of building, The results show that the nano insulation material vacuum insulated panels can be considered the optimum insulation in all cases when considering area saving as it achieved the maximum life cycle saving. Finally, the study reviewed the placing locations and installing insulation materials in buildings.enEnergy-saving,thermal insulation,life cycle costing,optimum thickness,payback periodMSA UniversityOctober University of Modern Sciences And ArtsArticle