The environment has played a key role to improve the living condition and develop the industry. In building industries, we should consider the environment and mitigate the environmental affect. For mitigating the its affect, various areas of building technology have been developed and applied into filed work. In addition, the process in applying into field requires to conduct the assessment of the environmental affect and improve its applied technology. A lot of assessment methods are proposed in evaluate the building condition such as post-occupancy evaluation, life cycle management and life cycle assessment. Among these assessment methods, life cycle assessment is effectively utilized the environmental affect in building life cycle. Therefore, this paper aimed at analyzing the energy consumption and $CO_2$ emission in building life cycle, using the life cycle assessment and application of the example in apartment housing. This study shows that the maintenance and the production of building materials stage shares most of the amount of energy consumption and $CO_2$ emission and therefore plays an important role to planning the building in terms of the life cycle. Second, the other stages brings about a very small amount. It is important to decide the building shape and contents to mitigate the environmental affect in terms of material, volume, the pattern of the energy use and others.