
A weight pocket (also called a sash box or window box) is the enclosed cavity within a sash window frame that houses the counterweights, pulleys, and cords of the traditional weight-and-pulley system.
Typically built into the side jambs of the window reveal, it allows the sashes to open and close smoothly while remaining hidden from view.
In heritage restorations, preserving or carefully repairing the weight pocket is essential to maintain authentic operation-especially when upgrading to heavier double-glazed sashes, which may require rebalancing with adjusted weights.


