In this paper we have considered a mathematical model to appraise the real feasibility of the last type of urban project. In particular we have tried to find some previsions about the effects produced by that kind of project in the urban contest. This model is founded on: -some categories of feasibility; these classes represent the various aspects of social welfare pursued by an urban project; -some weighed objects that represent the different needs of the community whom the project is intended to; -a verification about the attainment of aforesaid objects by the tested project. We have noticed that the statement of this model has common something with the theory of fuzzy sets.