The archival materials in the lower level of SLU’s Pius XII Memorial Library require 70 degrees within one degree and 45% relative humidity within three percent, year round. Protecting irreplaceable collections means the mechanical system has to perform consistently, without drift or approximation. G&W provided mechanical engineering design-build services for the four-room special collections upgrade, delivering a new Liebert air handling unit with 100% redundant refrigeration, independent reheat coils with SCR controls, steam humidification, and Johnson Controls campus automation integration. Fast-acting fire and smoke dampers protect the vault.