Glossary of Window & Door

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1 over 1; 2 over2; 8 over 8; 4 over 1 .etc Sash windows are commonly refered to by the number of glazed panes per sash. A one over one has only one pane of glass per sash and no glazing bars. A typical Georgian design of an 8 over 8 has 8 panes of glass in each sash, seperated by glazing bars. Its also not uncommon to have an uneven configurations such as 4 over 1 which are common in bay windows..



Argon Inert, nontoxic gas. Most common of the gases used to fill air spaces in double glazed units for improved insulating qualities.
Air leakage The rate of air movement around a window, door, or skylight in the presence of a specific pressure difference across it. It's expressed in units of cubic feet per minute per square foot of frame area (cfm/ft2). A product with a low air leakage rating is tighter than one with a high air leakage rating.

Number of views obtained from a bay window. E.g. "3 aspect bay window" is 3 windows joined at 90 degrees giving 3 views or aspects (forwards, left & right).

May also refer to the overall view that is obtained from a window. A 'front aspect bay window' has views over the front garden.

Annealed glass Float glass is the most common example of an annealed glass; during manufacture it is heated to a transition point and slowly allowed to cool. When broken it forms large, sharp jagged shards that can lead to serious injury. Most building codes have restricted its use in areas considered as high risk, such as low level glazing, bathrooms and doors.

Moulding around around a window or door. They serve to cover the join between the window and the surrounding wall.

Arris Sharp edges of square cut timber are lightly sanded to remove the arris or sharp point. This enables better paint adhesion.
Astragal (Glazing bar) commonly used to describe a glazing bar in a bookcase but occasionally used in ref to window glazing bars.
Awning Window

Casement window hinged at the top, that swings outward like an awning.



Bay window Grouping of windows that project from the face of the building. Square, splayed or bowed in plan. Single or double storey construction.
Bead moulding decorative moulding to the outside junction of the frame lining and brickwork.
Bead Stop Wooden strip against which a casement window closes.
Beehive Arm Fastener Sash Window Catch similar to a quadrant catch but with a turned 'beehive' knob.
Bonded glazing bar 2 section glazing bar to allow a double glazed unit to pass through. The outside part of the moulding is effectively a fake putty bead, bonded to the glass with a special adhesive glazing tape.
Borrowed light

Any panel that allows light to be 'shared 'into adjacent spaces. Commonly a high level glazed panel above internal doors.

Boston hinge Small hinge fitted to staff beads that allows the bead to swing out of position, giving easy access to the lower sash.
Bottom rail Bottom horizontal member of a sash or casement.
Bottom sash Sashwindows have a pair of sashes. An upper or top sash and a lower or bottom sash.
Bow window

Bow windows are curved when looked at from above, on plan. Often several standard 'flat glazed' windows are formed on a continuous bowed sill to create a bowed bay window. However for only the finest quality windows both the sashes and the glass are bowed to form a true bow window.

Box sash window Traditional weight balanced, vertically sliding window. Named because of the boxes built to contain the weights.
Brighton pattern fastener Sash window catch that offers better security over many traditional catches. Care must be taken on double glazed or thin sashes that the spring action does not hit the glazing..
Bull-Nose Wide semicircle profile shape. Commonly refers to the small indoor sub-cill where the architraves end.



Cambridge fastener (Meakins Fastener) Allows remote operation of the sash with the use of assistor cords and pulley's. Ideal for difficult situations where the catch is hard to reach.
Cane H shaped piece of lead or zinc used to link pieces of glass edge to edge as in leaded lights or zinc lights & stained glass work.
Carrier (Flat or 'T' carrier) Brown or white uPVC strip with a channel used to fix our pile weatherstripping.
Casement Window (Mullioned window) Window that opens on hinges attached to the frame. As the sash closes by pressing against the frame compression seals may used with lower air leakage rates than sliding windows.
Casing Another name for Architrave
Clerestory Window

(Clear story) Clestory windows form a narrow band and sit atop a high wall. The clerestory wall usually rises above any adjoining roofs. The word originaly referred to the upper level of a church.

Corbel A corbel is an architectural bracket or block projecting from a wall.
Conservation area Area of special architectural or historic interest,considered desirable to preserve.
Condensation Mist of water vapor that forms on any cold surface whose temperature is below the dew point. Altering air-flow by installing window seals can increase condensation. Mechanical fan extraction is the preferred way to remove excess water vapour.
Counter-balance Sash weight that is attached to a cord, over a pulley; to balance the weight of the glazed sash.
Cill (Sill) Lower horizontal section of a door or window frame. Also the horizontal member beneath a window or door, usually of brick or stone construction
Cross Window 4 light casement window with a transom. Many were replaced with sash in the 18 - 19 centuries.


A projecting point formed where two curves meet. Common in Gothic architecture they add extra decoration to window tracery and sculptural carvings.



Diocletian Window (Thermal Window) is a semi-circular opening divided into three by vertical mullions.
Double glazing

Two panes of glass separated by a sealed air space. This configuration offers significant improvements to the thermal efficiency of window glazing. The air space is often gas filled to further improve heat conductivity.

Double-hung (Sash window) Double hung indicates that both sashes are to operate.
Dormer window Vertical window with its own roof that projects through a sloping roof surface.
Draught excluders Weather seals attached to the bottom of doors.
Drip Groove cut into the underside of a cill to stop water running back into the building.
Drip stone (Label or hood mould) a continuous projecting moulding over a window.
Dry-glazing The use of glazing tapes, spacer blocks and wooden glazing bead instead of linseed putty.



Epoxy resin (Resin repair) Synthetic glue / filler used to make long lasting repairs on windows and doors.
Espagnolette Locking system found typically on french windows. Rods are controlled by knob mechanism having hooked ends that engage catches in the head and sill of the frame.



Façade Any side of a building, but especially an imposing or decorative one, facing a public space.
Fanlight Semicircle (or semi-elliptical) shaped sash above a door or window usually featuring radiating glazing bars, giving a fan like appearance. The term fanlight has been commonly adapted to include any small window found over a door.
Federation Australian architectural period c. 1890 - c. 1915. Federation style was, broadly speaking, the Australian version of the UK Edwardian Period.
Fenestrator Manually operated winding system to facilitate easier operation of heavy sash windows.


A word used to describe the window arrangement of a building.
Fitch fastener Sash window catch. This is the standard catch we use at Sash Window Specialist.
Fixed sashes A pair of sashes fixed shut. Often used in bay windows to maintain the aesthetics instead of using a single large glazed panel.
Fixed window Fixed panes that don't open. When installed properly they're airtight, but are not suitable in places where window ventilation is desired.
Flashing Weatherproofing that bridges joints formed by different materials or surfaces. Traditionally a sheet metal such as lead was used.
Float glass 90% of the worlds flat glass is now made using the Pilkington process. Glass is formed by floating the moulten glass on a bed of moulten tin. It produces a high quality glass with perfectly flat, parallel surfaces.
Frame (window) Outermost timbers of a window, jointed together and used to contain the window components as well as form a fixing with the wall.
Friction stay Side mounted hinge mechanism for casements that suspend the window open.
Frieze horizontal band that runs above doorways and windows or below the cornice. The frieze may be decorated with designs or carvings.

French window
Pair of casement windows extending to the floor and serving as portals.



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