Abstract: A glazed curtain wall construction for a commercial building is composed of a multiplicity of glass window units and glass panel units which are supported in stacked relationship by a series of vertical columns or mullions. Each unit is rectangular in configuration being composed of a header, a sill and a pair of jambs that connect the header and sill together. The sill of each unit is provided with a downwardly projecting flange which is received within a groove in the header of the next lower unit and the header is provided with an inwardly extending flange that defines a downwardly facing recess which is supported on dumbbells attached to the side surfaces of adjacent mullions. In addition, one jamb of each unit is formed with a vertical flange which is received within a groove in the opposite jamb of the next adjacent unit.