Abstract: A storm window assembly is provided for easy installation upon the exterior surface of the frame of a prime window of a building. The assembly is comprised of four track-like pathways adapted to slideably engage four storm window sashes and a screen sash. The pathways are of progressively larger rectangular perimeter going from the exterior to the interior borders of the frame, thereby permitting easy removal of the sashes for cleaning purposes. The several sashes have about half the height of the frame, and are arranged in a manner to create a dead air space within the assembly. A flange and associated resilient gasket is disposed outwardly from the frame in a manner to permit weatherproof abutment with the frame of the prime window without need for caulking.