Vertical sliding windows are a popular type of replacement sash windows. A vertical sliding window is an elongated window which consists of two sashes, one on top of the other. One or both of the sashes move vertically within the frame to open and close the window, allowing a maximum of 50% of the window’s size for open ventilation. Some sliding windows include one operable sash and one fixed sash, These are called single hung windows. Other vertical sliding windows, consist of two operable sashes and are called double hung windows.