The life cycle energy of a residential building consists of the embodied energy involved in the building materials and construction, and the operational energy of the building. Previous studies into the life cycle energy of buildings have concluded that embodied energy is a relatively small factor and can generally be ignored. A review and analysis of previous life cycle energy analysis studies was conducted re-examining this conclusion. This reevaluation has identified that this is not the case when considering climatic factors, and that in milder regions embodied energy can represent up to 25% of the total life cycle energy. The time value of carbon is generally ignored in life cycle energy analysis studies, however in a national emissions reduction regime, when the energy consumption is reduced, can become an important factor. Applying Net Present Value principles the impact of embodied and operational energy was analysed in the context of a future emissions target. It was demonstrated that embodied energy can represent 35% of the future emissions target of a building in a mild climate. The research highlights that a more wholistic approach is needed to achieve low life cycle energy buildings in the future.