One of the most important properties of a passively designed building is to provide thermal comfort conditions for users with a minimum heating energy cost. Therefore, primary parameters affecting heating energy consumption should be determined correctly during the design stage. Building envelope and operation period of the heating system are important parameters affecting total heating energy consumption in the building. In this study, an approach for the determination of the most convenient building envelope-operation period combination in relation to the life cycle cost and climatic comfort is proposed. For the application of the approach, total heat loss and life cycle cost of the building envelope-operation period combinations of a sample building, which is heated intermittently and used during underheated period of the year were calculated and combinations which provide thermal comfort during the occupation period with the minimum life cycle cost are determined as a most convenient combinations. This study is carried out in Istanbul, which is representative city for temperate-humid zone of Turkey. (C) 2005 Elsevier B.V. All rights reserved.