Venetian Window with Hollow Mullion and Mid Single Hung

When three pairs of sashes are used, the middle pair wider than the others it is called a Venetian Window. The vertical divisions between the adjacent pairs of sashes are called mullions.

If it is desirable to have all the sashes to slide the mullions must be hollow to provide room for the weights. With the arrangement of a mullion with provision made for one weight to balance the two sashes adjacent to it, the sash cord passes around a pulley fixed into the upper end of the weight. If one sash only slides and the other is fixed in the frame the window is single hung sash and frame window. When both sashes slide and are balanced by weights, the window is known as a double hung sash and frame window.