Building designers are constantly facing the problem on how to choose energy conservation options and how to implement them. This is especially true at the preliminary design stage when many important design decisions that significant affectly the energy performance are made. The Model National Energy Code of Canada for Buildings [MNECCB 1995] provides the guidelines for the energy-efficient building design. Knowledge-Based Systems are well suited for the computerization of the Code requirements. By linking to simulation models representing the real world environment, the KBS approach can potentially support most aspects of compliance checking provided in the energy Code. The objective of this research is to develop a systematic and integrated methodology to assemble a computer-based system that will perform as a design assistant. It will help architects and building designers at the preliminary design stage to compare current designs to the MNECCB in areas of the building envelope and lighting.