SUMMARY
The allocation method does value the building areas on the base of the exchange coefficient, but sometimes it is applied in an uncritical way. Following the traditional appraisal is it possible to precise the methodological conditions. The study means to demonstrate that the market value of the building area is obtained multiplying the construction cost by the ratio between the exchange coefficient and its complementary one. The new formulation considers the effective costs and proceeds distribution in the time, with the cash flows analysis, and moreover concurs to express convenience judgments for building area transactions.