Abstract: A window grille set of pre-fabricated tubular members of a uniform cross-section having flat top, bottom and side walls which are provided with means for their joinder in crossed relation to form a self-sustaining grille assembly in which said members serve in the manner of window sash mullions to provide it with multiple light openings. The mullion-like members are provided with interlocked cross-lapped joints at each point where they cross one another and where said members are angularly related to provide diamond-shaped "lights" the opposite ends of each contiguous pair thereof are held together in miter-jointed relation by a spring-biased clip inserted into the hollow mitered extremities of said paired members. In its assembled form the grille is designed to be installed as a unit and hermetically sealed within the space conventionally provided between the spaced panes of thermal insulated window sashes.

Abstract: A window construction comprising a master frame and a pair of glazed window sashes which are double-hung in the window frame for normal operation and are provided with means to permit inward tilting of the sashes for cleaning and servicing of the same as may be required. The master window frame and both of the sashes mounted therein are each formed of an assembly of sections having the same hollow cross-sectional shape throughout the lengths thereof to provide not only the master frame but also each sash with a perimetrally continuous plenum of confined air which effectively serves as a thermal insulating barrier. Each of the window sashes is fitted on its opposite side edges with hollow thermal insulating spring-pressed weatherstripping members which respectively resiliently engage and made weather-tight contact with vertically extending runways provided therefor in the opposite side rail members of the master frame.