Urban planning variants: a model for the division of the activated "plusvalue" between public and private subjects [Interventi in variante urbanistica: un modello per la ripartizione tra pubblico e privato del "plusvalore" conseguibile]

The establishment of the “extraordinary urbanization contribution” with Law no. 165 of 2014 requires regulating the division between public and private of the capital gains achievable from interventions on urban areas or buildings as variant or in derogation of the regulatory instruments in force. The “free interpretation” of the aforementioned directive left to regional and local decision makers – regarding a) the procedures for assessing the higher value generated by the urban planning variant compared to the pre variant situation and b) the exact percentage of the extraordinary contribution to be used – has led to a methodologically uneven and confused national panorama. This work aims to define and test a rational procedure for assessing the higher value activated by the intervention, comparing the situation before and after the urban variation, and to determine the amount of the gross floor area achievable with the transformation that the private subject is required to pay to the Public Administration, due to the percentage variation of the extraordinary contribution. Implemented with reference to the urban context of the city of Bari (Italy) and in line with the national and regional regulatory provisions on the matter, the proposed model adopts the logic of Operational Research in compliance with the physical urban constraints, the conditions of the real estate market and the interests of the public and private subjects involved. The results show that the determination of the percentage of the extraordinary urbanization contribution to be applied must be appropriately weighted, in order to ensure the financial convenience of the private part and the fair distribution of the efforts and benefits that can be achieved by the urban planning variant.