Upper sash detent latch for a double-hung window

Abstract From the Canadian patent

A building window includes a generally rectangular frame (22) having an upper rail (24) and opposed side rails (26 28). An upper sash (30) and a lower sash (32) are independently movably mounted in the frame. A pair of opposed spring detents (36 or 60) are mounted on the side rails adjacent to the upper rail of the frame. A pair of laterally opposed latches (38) are at upper corners of the upper sash at positions to engage the spring detents as the upper sash is moved to its fully raised position. The latches cooperate with the spring detents to hold the upper sash in its fully raised position and are releasable from the spring detents to permit lowering of the upper sash.