A building facade system for covering a building facade including a building wall and a window opening, comprising at least one window assembly mountable to mullions provided across the window opening and a plurality of wall assemblies surrounding the at least one window assembly, each wall assembly being independently mountable onto rails extending across the building wall. The at least one window assembly is configured to reduce thermal flow between an interior environment and an exterior environment, and includes a bypass insulating profile extending from a connection insulating profile externally towards a window panel and inwardly over an exterior profile, to define an air chamber between the bypass insulating profile and an inward surface of the exterior profile.