• Air Chambers – Small honeycomb spaces within the sash and frame which help to insulate and strengthen the window.
  • Air Infiltration – The amount of air that passes between a window sash and frame. In windows it is measured in terms of cubic feet or air per minute, per square foot of area. The lower the number, the less air the window lets pass through.
  • Argon Gas – An odorless, colorless, tasteless, non-toxic gas which is six times denser than air. It is used to replace air between the glass panes to reduce temperature transfer.
  • Awning Window – A top-hinged window that swings outward for ventilation.


  • Bay Window – An angled combination of three windows that project out from the wall of the home. The windows are commonly joined at 30- or 45-degree angles.
  • Bow Window – An angled combination of windows in 3-, 4- or 5-lite configurations. The windows are attached at 10-degree angles to project a more circular, arced appearance.


  • Cam Lock and Keeper – The mechanisms which pull the sash together when placed in the locked position.
  • Casement Window – A window with a side-hinged sash that opens outward for ventilation.
  • Compression Sills – Seals that can be squeezed tightly together between the moving sash and frame.
  • Condensation – The formation of moisture on the surface of the window.
  • Conduction – Heat loss in windows that occurs primarily through the edges of the glazing and through the sash and frames.
  • Convection – Heat loss that occurs due to air movement between the glazing of a window.


  • Dead-air space – The space between the panes of glass of an I.G. Unit.
  • Desiccant – A material used in insulating glass to absorb water vapor which causes fogging.
  • Double Hung Window – A window that has two operable sash which slide vertically.
  • Drainage Holes – Small openings designed to allow water to escape that might otherwise accumulate in a window’s sill.


  • ENERGY STAR® – ENERGY STAR® is an independent government program establishing a standard set of guidelines to recognize the energy efficiency of various products. ENERGY STAR® guidelines are used in conjunction with a variety of building materials, including windows and patio doors. Over the past ten years, ENERGY STAR® guidelines have helped double the efficiency of windows they endorse.


  • Full Frame Removal – An installation procedure in which the entire window assembly is removed right back to the rough opening and replaced with a completely new window.
  • Fusion-welded – The process of joining materials by melting them together with extreme heat (over 375 C), resulting in the materials uniting into a one-piece unit.


  • Glazing – The process of sealing the glass to the sash.
  • Glazing Bead – A strip of vinyl which surrounds the edge of the glass and holds it in place in conjunction with other sealants.
  • Grills – Decorative horizontal or vertical bars installed between the glass panes to create the appearance of the sash being dividing into smaller lites of glass.


  • I.G. Unit (Insulating Glass Unit) – Two or more lites of glass separated by a spacer and hermetically sealed at the glass edges.


  • Jamb – Vertical sections of the main frame.


  • Lite – A unit of glass in a window.
  • Low E (Emissive) Glass – A thin metallic layer, only several atoms thick, applied directly to the glazing surface the purpose of which is to reflect long wave energy back towards the source.


  • Mullion – A vertical or horizontal frame member that separates two or more sash, two or more fixed lights or a combination of sash and fixed lights.


  • Obscure Glass – Glass that has been made translucent instead of transparent.


  • Patio door – A glass door that slides open and close on adjustable tandem rollers. Available in 2- or 3-lite configurations with the operable panel available in any position.
  • Picture Window – A window that has no moveable sash.


  • R-value – Resistance a material has to heat flow. The higher the R-value, the greater the resistance, the better the insulation. R-values are the reciprocal of U-values (R-value of 4 is equal to U-value of 0.25)
  • Radiation – Wave energy transmitted directly from one object to another through the atmosphere or through transparent or translucent materials. The energy radiated is transmitted, absorbed, reflected or a combination of all three.


  • Sash – The part of the window which contains the glass.
  • SAWDAC – Siding and Window Dealers Association of Canada
  • Shims – Wedges, usually about 2″ wide used to position the window into the opening and ensure it is level, square and plumb.
  • Sill – The horizontal, bottom section of the main frame.
  • Sill Extension – An extrusion that is attached to the bottom of the window to cover the gap between the sill and the rough opening.
  • Slider Window – A window in which the sash move horizontally. Sliders are available in a 2- or 3-lite configuration, with the 3-lite having operable end vents.
  • Solar Heat Gain – The percentage of heat gained from both direct sunlight and absorbed heat. The smaller the number, the greater the ability to reduce solar heat gain.
  • Spacer – Material placed between two or more pieces of glass in order to maintain a uniform width between the glass, and prevent sealant distortion.
  • Sweep Sill – A flexible fin usually made of rubber or polypropylene which is fastened to either the movable sash or the stationary frame and sweeps against the opposing component to form a barrier.


  • Tempered Glass – Glass when broken, it breaks into pebbles instead of shards.
  • Thermal Break – An insulating material applied to a high conducting material to slow the transfer of heat.
  • Tilt Latch – Mechanism that unlocks the sash and allows it to tilt in from the main frame.


  • U-value – Amount of heat transferred through a material. The lower the U-value, the slower the rate of heat flow and the better the insulating quality. U-values are the reciprocal of R- values. (U-value of 0.25 is equal to R-value of 4)


  • Warm Edge Spacer – Spacers made from insulating material such as foam, butyl, thermo- plastic, or thermally improved metals and therefore conduct significantly less heat energy than standard spacers.
  • Water Leakage – The penetration of water that would continuously or repeatedly wet parts of a building or components not designed to be wetted.
  • Weather-stripping – Material used to form a weather-resistant seal around operable sash