A manufactured assembly of a frame, sash, glazing and necessary hardware, made to fit an opening in a wall. Components of a window may include the following:

  • Window sill: horizontal member at the base of a window opening.
  • Window head: horizontal member at the top of a window opening.
  • Window jamb: either of the vertical members at the sides of a window opening.
  • Mullion: A vertical member between the glazed units.
  • Rail: A horizontal member between the glazed units.
  • Glazing: The glass portion of the window.
  • IGU: Insulated glazing unit. Double or triple panes of glass sealed together to provide insulation value.  The still gas between the panes acts as the insulation.
  • Condensation track: a channel at the interior sill level of the window intended to intercept small amounts of water condensing on the interior surface of the glass.


Related terms: Condensation, Fenestration, Jamb

Related resources: The Future of Window Technology...Is Here!; Windows and Occupant Comfort; BA-1203: Measure Guideline—Wood Window Repair, Rehabilitation, and Replacement; Info-709: What's Wrong with this Project? Extra Window Framing; Info-406: Air Sealing Windows