The Mediterranean climate is characterized by a high level of the solar resource in winter and some coolness of the nights in summer, which offer a good opportunity for thermal comfort achievement at low energy cost and reduced CO2 emissions, provided that an appropriate design of the building envelope is adopted. It has thus been decided to implement some regulations in three countries of North-Africa for controlling the heating and cooling loads. The study described in this paper has been conducted in the frame of this project. It has two objectives: to define adequate indicators for the thermal performance of buildings during both the cold season and the hot one, and to develop a standard calculation procedure for these indicators. The developed procedure, CHEOPS, is fast and requires minimum input data; it is very easy to use, the steps for calculating the cooling and heating coefficients being almost the same. The transmission losses and the solar gains are clearly identified; this fact can contribute to a better understanding by the designer of the effect of each parameter, leading him towards the appropriate trade-offs between summer and winter considerations. (c) 2004 Elsevier B.V. All rights reserved.