Between preservation and innovation: working on the pre-existing

The debate between preservation and project, on which we still discuss, is based in recognizing the historicity or planning skill as a distinctive element. While in the past the historical buildings were objects of aesthetic value and in consequence of it they became objects of preservation and restoration, today it seems that the analysis falls mainly on the object itself , particularly recognizing its uniqueness and irreproducibility. In any case the most important question is: what are the limits of the architect's work, when he must operate on a historical heritage? The paper presents some different approaches starting not from abstract conceptions given "a priori", but from methodological experiences actually carried out in the restoration sites.