Abstract: A double hung window assembly (10) having a perimeter frame assembly (11) and a vertically slidable upper sash (12) secured in its raised or closed position by fusible link means (26) to the frame assembly (11). The vertically slidable bottom sash (13) has releasable catch means (42) for securing it in its lowered or closed position. Stop means (30) adapted to prevent the upper sash (12) moving beyond the lower sash (13) is present. Biasing means (40) are included with the bottom sash (13) to provide an elevated bias to it, sufficient to hold the bottom sash (13) in selected open or raised positions but insufficient to hold both the upper (12) and lower (13) sashes in an elevated position upon release of the fusible link (26) whereby when the assembly (10) is used and the bottom sash (13) is elevated, both sashes will move to their lower positions to provide a smoke ventilating opening thereabove.