The window is a building element that is predominately used to provide natural light and fresh air. It includes vertical opening but also horizontal opening such as skylights or light domes. It includes constructions with swinging, pivoting, sliding, or revolving panels and fixed panels. A window consists of a lining and one or several panels. A window can: 

• be a "free standing" window, contained in an IfcSpatialElement such as an IfcBuildingStorey.
• fill an opening, typically in a wall. The window will then have a FillsVoids attribute which uses the IfcRelFillsElement relationship to relate the IfcWindow with the IfcOpeningElement;
• be part of an element assembly, typically an IfcCurtainWall. The window will then have a Decomposes attribute which uses the the IfcRelAggregates relationship to relate the window with the assembly of elements;

The IfcWindowType specifies parameters which are common to all of its occurrences of IfcWindow:

• the partitioning type (single panel, double panel, triple panel, more panels)
• the operation type (swing, tilt and turn, pivot revolve, fixed casement, etc.)
• the window panel hinge side (by using two different styles for right and left opening windows)
• the particular attributes for the lining by the IfcWindowLiningProperties
• the particular attributes for the panels by the IfcWindowPanelProperties

This concept can be applied to the following resources:

• Lining - Indicates that the material constituent applies to the window lining
• Framing - Indicates that the material constituent applies to the windows panels(s); if not provided, the 'Lining' material information applies to panel(s) as well
• Glazing - Indicates that the material constituent applies to the glazing part

If a single IfcMaterial is referenced, it applies to the lining and framing of the window. 

• The PlacementRelTo relationship of IfcLocalPlacement points to the local placement of the same element (if specified), in which the IfcWindow is used as a filling (normally an IfcOpeningElement), as provided by the IfcRelFillsElement relationship
• If the IfcWindow is not inserted into an IfcOpeningElement, then the PlacementRelTo relationship of IfcLocalPlacement points (if specified) to the local placement of the same IfcSpatialStructureElement that is used in the ContainedInStructure inverse attribute or to a referenced spatial structure element at a higher level
• If the relative placement is not used, the absolute placement is defined within the world coordinate system

The window profile is represented by a three-dimensional closed curve lying in the xz plane. The profile is used to apply the parameters of a parametric door representation. The following attribute values for the IfcShapeRepresentation holding this geometric representation are used:

• RepresentationIdentifier : 'Profile'
• RepresentationType : 'Curve3D', only a single closed curve is contained in the set of IfcShapeRepresentation.Items

A 'Profile' representation has to be provided if:

• A parametric representation is applied to the window AND
• One of two options:
  • the window is 'free standing'
  • the opening into which the window is inserted is not extruded horizontally (i.e. where the opening profile does not match the window profile)

This concept can be applied to the following resources:

• Pset_DoorWindowGlazingType
• Pset_WindowCommon

This concept can be applied to the following resources:

• Qto_WindowBaseQuantities

The IfcWindow, as any subtype of IfcBuildingElement, can participate alternatively in one of the two different containment relationships:

• the Spatial Containment (defined here)
• the Element Composition

The IfcWindow can also be connected to the IfcOpeningElement in which it is placed as a filler. In this case, the spatial containment relationship is provided, see image below. 

The parameters that defines the shape of the IfcWindow, are specified at the IfcWindowType and the property sets, which are included in the IfcWindowType. The IfcWindow only defines the local placement which determines the opening direction of the window. 

The overall layout and its symbolic presentation of the IfcWindow is determined by its IfcWindowType.PartitioningType. The type determines the number and position of window panels. Depending on the type, the appropriate instances of IfcWindowLiningProperties and IfcWindowPanelProperties are attached in the list of HasPropertySets.