The building sector is one of the fastest growing in terms of energy consumption. To guarantee energy savings and to reduce carbon dioxide (CO(2)) emissions, building energy conservation assessment is an important option. A building energy conservation assessment will strongly promote development of the building's thermal characteristics and application of new energy conservation technologies and products. Because of the unquantifiable and incomplete information of evaluation criteria, a multihierarchical gray evaluation methodology is proposed for building energy conservation assessment. To determine the weights of the factors, a linear combination weighting method combining an analytic hierarchical process (AHP) method and the technique for order preference by similarity to ideal solution (TOPSIS) method is proposed. The integrated assessment results and the integrated assessment values are calculated, and a building energy conservation star is proposed and determined. Then, an example is used to illustrate the proposed approach and the proposed method is validated. The results demonstrate the engineering practicability and effectiveness of this proposed method. DOI: 10.1061/(ASCE)EY.1943-7897.0000041. (C) 2011 American Society of Civil Engineers.