A catastrophic risk model has been developed to evaluate, building by building, the probabilistic losses and pure premiums of different portfolios. The model includes a hazard module, an exposure module, a vulnerability module and a risk module. A brief summary of the methodological approach adopted for catastrophic risk assessment and an improvement methodological approach for the vulnerability assessment of building structures is presented. Dynamic nonlinear or simplified nonlinear analysis, the consideration of multiple damage functions for different types of components of the construction and a repair cost methodological approach are proposed in order to integrate the total economic losses for the building, for different performance levels of analysis. The methodology is illustrated with a one-story, one-bay reinforced concrete moment resisting frame with unreinforced masonry infill walls. Preliminary conclusions and recommendations are presented for the implementation of the proposed methodology.