Glazing glossary
Plain definitions of the terms used in window, door and glass specifications.
- Argon
- An inert gas used to fill the cavity of sealed units, reducing heat loss compared with air.
- Astragal bar
- A glazing bar fixed to the glass to look like a traditional bar dividing the panes.
- Baypole
- A structural or coupling post used at the joints of bay and bow windows.
- Bead
- The strip that holds the glass in a frame or sash.
- Bifold door
- A door made of panels that fold and slide to one or both sides.
- BS EN 1279
- The standard for insulating glass units (sealed units).
- BS EN 12150
- The standard for thermally toughened safety glass.
- BS EN 12600
- The pendulum impact test used to classify safety glass.
- BS EN 13830
- The product standard for curtain walling.
- BS EN 14351-1
- The product standard for external windows and pedestrian doors.
- Casement
- A window with sashes hinged at the side or top.
- Cill
- The horizontal section at the bottom of a window that sheds water away from the wall.
- Clear opening
- The unobstructed width or area available when a door or window is open.
- Competent person scheme
- A scheme that lets registered installers self-certify building work, such as FENSA or Certass for windows.
- Composite door
- A door with a GRP skin over a solid insulating core.
- Critical location
- A place where glazing must break safely, be robust or in small panes, or be protected under the building regulations, such as in and beside doors and at low level. Toughened or laminated safety glass is the usual answer.
- Curtain walling
- A non-structural glazed facade hung off the building structure.
- Doorset
- A complete door supplied with its frame, hardware and threshold.
- Dual colour
- A frame finished in one colour outside and another inside.
- Egress hinge
- A hinge that lets a sash open to a full right angle for escape.
- Espagnolette
- A locking mechanism that engages at several points along the sash.
- Euro cylinder
- The common profile of lock cylinder used in uPVC and composite doors.
- Fixed light
- A pane or section of a window that does not open.
- Flush sash
- A sash that closes flush with the outer frame.
- Friction stay
- The hinge mechanism on many casement windows that holds the sash open.
- Georgian bar
- A glazing bar between the panes of a sealed unit, dividing the glass into smaller sections.
- GRP
- Glass-reinforced plastic, used as the outer skin of composite doors.
- Handing
- Which side a door or sash is hinged on and which way it opens.
- Heat-soak test
- A process that reduces the risk of spontaneous breakage in toughened glass.
- IGU
- Insulating glass unit, another name for a sealed unit.
- Interlayer
- The plastic layer that bonds the panes of laminated glass.
- Laminated glass
- Glass made of two or more panes bonded with an interlayer that holds it together if broken.
- Low-E glass
- Glass with a low-emissivity coating that reflects heat back into the room.
- Mullion
- A vertical member dividing a window frame.
- Notifiable work
- Building work that must be certified by a competent person scheme member or approved by building control.
- Obscure glass
- Patterned or textured glass that lets light through but blocks a clear view.
- PAS 24
- A security test standard for doors and windows.
- Polyamide thermal break
- An insulating strip separating the inner and outer parts of an aluminium frame.
- Powder coating
- A durable paint finish applied to aluminium and cured with heat.
- PVB
- Polyvinyl butyral, the most common interlayer in laminated glass.
- RAL
- A colour reference system used to specify powder-coat colours.
- Rebate
- The recess in a frame or sash that the glass sits in.
- Reveal
- The side of a wall opening, between the frame and the face of the wall.
- Roof lantern
- A raised glazed structure set on a flat roof to bring in daylight.
- Sash
- The opening part of a window that holds the glass.
- Sealed unit
- Two or more panes separated by a spacer and sealed around the edge.
- Shoot bolt
- A bolt that locks a door leaf into the head and threshold.
- Spacer bar
- The strip that separates the panes of a sealed unit.
- Stallriser
- The solid panel below the glass on a shopfront.
- Structural opening
- The opening in the wall before the frame is fitted.
- Threshold
- The bottom part of a door frame that you step over.
- Tilt and turn
- A window that tilts inward from the top or turns inward on side hinges.
- Toughened glass
- Heat-treated safety glass that breaks into small pieces.
- Traffic door
- A single panel in a bifold set that opens like a normal door.
- Transom
- A horizontal member dividing a window frame.
- Trickle vent
- A small vent in the frame providing background ventilation.
- U-value
- A measure of heat loss through a building element, in W/m²K. Lower is better.
- uPVC
- Unplasticised polyvinyl chloride, the material used for most replacement window frames.
- Upstand
- The raised kerb a roof lantern or rooflight sits on.
- Warm-edge spacer
- A spacer bar made from less conductive materials than aluminium, reducing heat loss at the glass edge.
- WER
- Window Energy Rating, a band from A++ to E combining heat loss, solar gain and air leakage.
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