A casement is a window that is attached to its frame by one or more hinges at the side. They are used singly or in pairs within a common frame, in which case they are hinged on the outside. Casement windows are often held open using a casement stay. Windows hinged at the top are referred to as awning windows, and ones hinged at the bottom are called hoppers.

Casement windows, including awning and hopper types, “generally have lower air leakage rates than sliding windows because the sash closes by pressing against the frame.”

Casement windows are also excellent for natural ventilation strategies, especially in hot climates. Casements allow more control of ventilation than flush-opening windows. They can be hinged to open outward and angled in order to direct breezes into the building.