To operate on the existing is a complex matter which involves many entities with different expertises and specific skills. Various disciplines meet themselves around a shared desk, with the aim of connecting informations for the development of a conscious design. The preservation requires a thorough knowledge of artefacts; from this perspective the non-destructive diagnostics drives the conservation plan in its entirety, by collecting data before, during and after the intervention. The diagnostic data collection and their systematic storage, easily updated, available and comparable, become a prerequisite for a correct approach to the buildings, which can lead to a critical understanding of phenomena in progress and to a suitable project. In this paper are presented some recent experiences which show the use of information technologies for the acquisition of diagnostic data, for their processing, management and subsequent graphic representation in order to make them easily comprehensible and interpretable, assuring their diffusion.