Optimal insulation thickness of common classic and modern exterior walls in different climate zones of Iran

Insulation thickness optimization has become a prominent factor in building design for energy saving. This study aims to determine ideal insulation thickness of the external wall, energy saving, and payback period of investment in all climate zones of Iran. A classic gray brick wall and three modern walls (Hollow clay block, LECA block, and AAC block) were selected by considering four cardinal orientations. Eight cities were chosen as representatives of all climate zones. Optimization was performed using life-cycle cost analysis method along with a numerical solution to determine the transmission load. Results revealed that the use of thermal insulation in the AAC block wall, which is one of the common modern walls in Iran, is not economical in some cities. The maximum insulation thickness in Iran is not more than 4 cm which is much lower than the reported values for other countries. Also, the figures for energy saving and payback period in Iran are very different. This is due to the economic structure and low energy costs in this country. This study confirms the requirements in reforming regional energy policy and pricing mechanisms as a roadmap for insulation application in building envelope. •Life-cycle cost analysis method was applied for insulation thickness optimization.•Optimal insulation thickness for some common classic and modern walls were compared.•Some modern walls need no insulation in several climate zones of Iran.•Energy saving was 69% and payback period was 3.8 years at best.