The need for a simple, rational and instructive model of seismic capacity evaluation of existing buildings is stressed and the advantages of using understrength and overstress coefficients are illustrated. Identification and classification of understrength and overstress parameters of earthquake behaviour of RC buildings in Greece is presented, based on extensive surveys after the Volvi (1978), Magnissia (1980) and Alkyonides (1981) earthquakes. These parameters apply equally to RC buildings in other geographical areas. Distribution of frequencies for the different types and degrees of understrength and overstress problems in Greek RC buildings is also given. Tentative detailed criteria for the assessment of λ coefficients and weighting factors are developed. Based on ø and λ coefficients and on weighting factors, the general form of a self-contained model for seismic capacity evaluation of low to medium rise RC buildings is developed, which supplements the already existing models for the case of simplified modelling. It is concluded that, although a new self-contained model has been developed, more research is needed for reliable assessment of seismic capacity of RC buildings.