The National Library of Greece was established in 1829, and in 1903 moved to Vallianeio, an imposing neoclassical building in the center of Athens. The building comprises of three wings, left and right wings serve as storage areas, whereas the center wing hosts the main reading room. Similarly to historical buildings, Vallianeio was designed to passively control the interior climate. For more than a century, reading rooms and working areas have been periodically heated or cooled to create a comfort zone for the occupants. In 2006, the Stavros Niarchos Foundation announced its plans to fund the development of the Stavros Niarchos Foundation Cultural Center (SNFCC), that included new facilities for the National Library, the National Opera and Stavros Niarchos Park. In 2016, SNFCC was the first large-scale cultural project to achieve LEED Platinum certification in Europe. The goal was to integrate active and passive technologies that make SNFCC one of the world’s most environmentally sustainable buildings. In this context, the new facilities aim to provide suitable conditions for the collections’ long-term preservation. In 2018, after the massive endeavor of collections’ transfer from Vallianeio to SNFCC, the early preservation activities focused on achieving a smooth transition to the new climate and storage facilities. The goal set was to maximize the building’s potential for efficient energy use. Starting with identifying and documenting the strengths and weaknesses of the storage areas (close and open bookstacks), the following step was to assess the indoor and outdoor environment, leading to taking measures and launching new projects for improving the collections’ storage conditions. Within this new and challenging context, this paper presents the environmental documentation that was launched due to the transfer project and was enriched with further projects at the new premises, along with the reasoning and argumentation over collections’ preservation planning demands and the actions taken so far to raise awareness and to classify preventive conservation as a critical fundamental action.