This style of windows has movable panels. The frame is formed with one or more panels, the glass in the panels are separated by strips of wood. When there are two pieces of glass in the frame they are called double glazed sash windows. The two panes are filled with air or nontoxic gas between them.
Brian Shaw
Sash windows are generally found in Victoria or Georgian era houses and have been there for centuries. Because they are made from wood, they can be susceptible to rot and distortion and may need to be repaired or replaced over time. Many people do not realize that repairing your sash windows is better for the environment than replacing them and also could save you some money too?