A literature survey on buildings’ life cycle energy use was performed, resulting in a total of 60 cases from nine countries. The cases included both
residential and non-residential units.Despite climate and other background differences, the study revealed a linear relation between operating and total
energy valid through all the cases.Case studies on buildings built according to different design criteria, and at parity of all other conditions, showed that
design of low-energy buildings induces both a net benefit in total life cycle energy demand and an increase in the embodied energy. A solar house
proved to bemore energy efficient than an equivalent house built with commitment to use ‘‘green’’materials. Also, the same solar house decreased life
cycle energy demand by a factor of twowith respect to an equivalent conventional version, when operating energywas expressed as end-use energy and
the lifetime assumed to be 50 years. A passive house proved to be more energy efficient than an equivalent self-sufficient solar house. Also, the same
passive house decreased life cycle energy demand by a factor of three – expected to rise to four in a new version – with respect to an equivalent
conventional version, when operating energy was expressed as primary energy and the lifetime assumed to be 80 years.