Sash windows are a type of window design that features two or more movable panels, or "sashes," which slide vertically within a frame. This design allows for easy opening and closing, providing ventilation while maintaining a classic aesthetic. Sash windows are commonly found in historic buildings and are often made of wood, although modern versions can also be made from materials like uPVC. These windows can be single-hung, where only one sash moves, or double-hung, where both sashes can slide. Sash windows are appreciated for their traditional charm and can enhance the character of a home while offering practical benefits like energy efficiency when properly maintained.