In this article, generic objects are introduced into material databases of building simulation tools. A generic object has the common characteristics of one type of specific object and can represent specific ones in the simulation. The application of generic objects only requires some general design information; thus, it is convenient for the simulation users who do not have a detailed knowledge of building specification in the early design stage. First, the method to uncover the underlying cluster structure in the dataset is illustrated. Clustering of the objects depends on the adopted clustering variables and clustering procedure. Therefore, different clustering techniques are applied to agglomerate specific materials into different clusters, and the clustering solutions are compared for validation. Generic synthesis is then conducted to derive the generic material from each identified cluster. The approach on how to apply generic materials to fill in missing values of the incomplete material data is also described.