The hung window incorporates a heavier 4 inch deep frame which allows for smooth operation of the bottom sash to move up to open and allow air flow. This assembly offers 3/4 hour Underwriter’s Laboratory rated protection.. This larger single hung is designed and tested to be self-closing in the event of heat rise from nearby combustion. Ideal for inclusion in NFPA 80 and building code requirements for protective openings in rated walls.