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Last edited 02 Apr 2021
Window frames are made from many different types of materials, including timber, aluminum, pvc, steel, aluminium and so on. These materials provide different aesthetic, structural, maintenance and efficiency characteristics.
 Three parts of a window frame
Generally, a window frame is a combination of three parts:
- Head, which is the horizontal strip at the top of the frame. This is sometimes referred to as the first mullion, head jamb or headjamb. It may be located directly below a lintel.
- Jambs, which are the vertical sections of the frame. Jambs can be fitted with jamb liners to improve air tightness.
- Sill (or cill), which is the horizontal strip along the bottom of the frame. It is sometimes referred to as a window ledge (or stool of the window).
- Mullion, which is the vertical bar within the frame that serves to separate two casements. Mullions can be used for decorative purposes, or to allow the combination of smaller window units into larger compositions, or to provide structural support to an arch or lintel. They allow larger openings to be sub-divided into smaller windows which are technically easier to manufacture and less expensive.
- Transom, which is a horizontal bar within the frame that separates two casements. Together, with mullions, they provide a rigid support to glazing.
 Box sash window frames
- Architrave, which is the horizontal or vertical moulding that forms the surround to a window frame, typically internally within the room.
- Inside lining, which is the inside face of both the sides and head of the window box frame.
- Outside lining, which is the external face of the window frame or box.
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