Behind the Dome: The Hidden Roofs of Brunelleschi’s Old Sacristy. A Digital Survey Approach to Medieval Construction in the Renaissance

This paper investigates the Old Sacristy of San Lorenzo in Florence, a renowned icon of Renaissance architecture. Beyond its celebrated form, this research leverages an extensive digital survey (TLS, UAV) to analyse the ‘unseen’ spaces of the building, particularly the attic and roof voids. The analysis, conducted through a critical process based on a high-resolution 3D laser-scanner survey, revealed unequivocal material evidence of the building’s original roofing system. The finds consist of clear wall-traces of double-pitched (gabled) roofs over the scarsella (apse) and independent coverings for the side chapels. This system, now concealed, is technically and morphologically tied to medieval construction methods. The paper presents the 3D reconstruction (via NURBS and HBIM) of this lost morphology, demonstrating how the subsequent construction of the basilica buried the Sacristy’s original ‘temple’ volume. Furthermore, it analyses the consequences of this stratification, which included the blocking of original windows, thus radically altering Brunelleschi’s intended internal lighting scheme. The digital methodology applied here provided incontrovertible, tangible proof to confirm and detail what had previously been only a historical hypothesis.