A building facade system includes framework having shelf members secured to the floor slabs. The top terminal ends of vertical mullions are fastened to the shelf members, thereby hanging the mullions therefrom. Horizontal support members fastened to the mullions support infill panels and are coupled to shelf members which are on the below floor slab. Intermediate support members fastened to the mullions support slab edge cover panels. Posts are fastened to the shelf members and are secured to the floor slabs within troughs formed with embedded channels. The posts are horizontally and vertically adjustably fastenable to the shelf members. The shelf members are thereby also horizontally and vertically adjustable relative to the floor slabs. Terminal edges of the floor slabs can project into mullion cutouts.