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Parts of casement and sash windows explained

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There is a lot to think about when it comes to choosing windows for a property. They must operate effectively and fulfil an important function, but consideration must also be given to issues such as safety, noise reduction and energy efficiency. 

Two of the most common styles of window are casement and sash, and the choices don’t end there. Once the type of window has been selected, there are a wide range of finishes, hardware and decorative features to then choose from.

Knowing the correct terms for different parts of a window can help avoid any confusion. Here is an illustration of both a casement and a box sash window, with the key components highlighted and explained.


Parts of a casement window – glossary of terms

  • Fanlight – This is the name given to a smaller opening section found at the top of the window, which is typically rectangular in shape.
  • Window frame – Collective term used to describe the head running along the top of the window, the cill running along the bottom and the two vertical jambs on either side. This forms the outer surround of the window.
  • Head – Sometimes known as the first mullion. The horizontal bar across the very top of the window frame.
  • Top Rail – The name of the horizontal bar across the top of the casement.
  • Bottom Rail – The larger horizontal bar across the bottom of the casement.
  • Casement - The casement is the part of the window that opens, in which the glass sits.
  • Stile – The vertical edges of a casement.
  • Jamb – The two vertical sections running up the outer edge on each side of the window frame.
  • Cill or sill - Sits horizontally across the bottom of the window frame.
  • Mullion – The vertical bar that sits vertically within the frame and separates two casements, for example a fixed pane and opening casement.
  • Transom - A horizontal bar that separates two casements, for example a fixed pane and a fanlight casement.
  • Direct glaze – This is where the aperture for a casement is directly glazed with glass without a casement.


Parts of a box sash window – glossary of terms

  • Architrave - This refers to the moulding on the outer most edge of the window frame, typically internally within the room.
  • Top rail - The name of the horizontal bar across the top of the sash that opens.
  • Staff bead - The moulded bead that is attached to the inside lining which holds the two sashes in place so they slide well.
  • Glazing – The glass panels used within a sash.
  • Meeting rail - The name of the horizontal bar that sits across the top of the lower sash and the bottom of the upper sash. The meeting rails of both sashes meet together when the window is closed.
  • Inside lining - The inside faces of both the sides and head of the window box frame.
  • Sash bars – Sometimes referred to as glazing bars or sash-gut, they separate the panes of glass within any sash that has more than one pane.
  • Sash stiles – Run vertically up both sides of a sash.
  • Window board or nosing – Usually referred to as nosing in the context of a sash window, as there often isn’t the depth for a full windowboard due to box sashes being fitted behind the outer skin of bricks.
  • Cill or sill - The external horizontal bar that reaches across the bottom of the whole box-frame and directs water away from the window.
  • Horn - A decorative feature often found in traditional sash windows, the horn is a short extension of the top sash stiles at the meeting rails that strengthens the joint.
  • Bottom rail - The larger horizontal bar situated across the bottom of the lower sash.
  • Outside lining - The external face of the window frame or box.

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For more information or advice on windows for traditional, contemporary or renovation projects, call our customer services team on 01722 337040 or email info@salisburyjoinery.com