Sash windows are a type of window that slides vertically up and down in their frame to allow for better air circulation and control. They consist of two or more movable panels, known as "sashes," that are counterbalanced by weights or springs. These sashes are typically made of timber, although modern sash windows can also be made from uPVC or aluminium.

As well as being a classic feature of many period properties, sash windows are also known for their energy efficiency. Their tight-fitting design ensures that cold air is kept out in winter, while they also enable air to circulate freely during the hot summer months.