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Abstract: In this paper life cycle energy (LCE) demand of a residential building of usable floor area about 85.5m2 located at Hyderabad (Andhra Pradesh), India is evaluated under different envelopes and climates in Indian context. The house is studied with conventional (fired clay) and alternative wall materials (hollow concrete, soil cement, fly ash and aerated concrete) under varying thickness of wall, and insulation (expanded polystyrene) on wall and roof. The house is modelled for five different climatic zones of India, i.e. hot and dry, warm and humid, composite, cold and moderate. Study suggests that alternative wall materials alone (without insulation) reduce LCE demand of the building by 1.5–5%. Aerated concrete (AC), as wall material, has better energy performance over other materials. LCE savings are significant when insulation is added to external wall and roof. It varies from 10% to 30% depending on the climatic conditions. Maximum LCE savings with insulation are observed for warm and humid climate and least for moderate climate. For same thickness of insulation, LCE savings are much more with roof insulation than wall insulation. But wall insulation is found to be preferable to a thicker wall. It is also observed that there is a limit for thickness of insulation that can be applied on external walls and roof from life cycle point of view. This limit is found to be about 10cm for composite, hot and dry, warm and humid, and cold climates and 5cm for moderate climate. [Copyright &y& Elsevier]