Glossary of Technical Terms

The A to Z of words, terms and phrases used in the windows and doors industry.


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Air gap or Cavity gap
The space between the two panes of glass in an insulated glass unit.

The facing timber placed internally below the window sill.


Beveled facing, cut at an angle.

Bottom glazing bead
The lower of the moulding or stops around the window frame to hold the glass in place.


In double glazing, the space between the two panes of glass.


Internal engineered timber windo sill and surround, pre-finished in white paint.


Internal finishing timber fixed to. the perimeter of the window surround

Far East
Internal haardwood window sill and surround sourced from the managed woodlands across the Far East.

Fit or Fitting
Given the need to manufacture each product to your specification, and to then chack that the product is perfoming satisfactorily within your property, we distinguish betwee initally fitting the products to your property and our certification that the installation of each product has been completed.

The term we use to describe the type of timber or uPVC used for the window sill and surround internally, to complete the installation.


Georgian bar
Glazing in the style of Georgian architecure, i.e. to give the effect of small pane windows. Georgian bars are contained within the double-glazed unit.

A shading coefficient used to measure the solar energy transmitted through a glass pane. Together with the u-value, it gives a value of the thermal properties of an IGU.


Insulating glass unit, made from two or more glass panes seperated by a spacer bar and hermetically sealed along the edges. Also know as a double-glazed unit or a triple-glazed unit, depending on how many panes of glass are used.

The exposed area between the window frame and the internal edge of the window opening – usually finished in timber, plasterboard or uPVC.


Kicker Plate
To protect the base of the door from everyday wear and tear, fitted externally.


In reference to the frames, a membrance used to give a choice of colour and texture, applied to the uPVC frame e.g. oak, rosewood or anthracite grey.

In reference to glass, a specialy manufactured type of security glass whereby two pieces are bonded together with an interlayer of Polyvinyl butyral.

A glazing style to resemble leaded windows, i.e. to give the apperance that the window is made up of smaller sections joined by lead.


The vertical bar dividing the window into left and right parts.

Mid or Bottom Rail
Door framing material across the centre or bottom of the door. A common example of the use of such material would be to provide a letterbox.


Night Vent or Trickle Vent
To allow safe, regulated ventilation, usually in accordance with building regulations.


Obscure Glass
Can be annealed or toughened and had a design applied to it, often used in athrooms and doors. Also known as figured glass.

Opening Sash
The opening part of the window.

Ogee facing, heavily countoured shape.

Outer Frame
The outer part of the window to which the opening sashes are fastened.


Plant or Astragal
Glazing in the style of Georgian astragals i.e. to give the effect of small pane windows. Plant-on astragals are applied to the surface of both the inside and outside panes of glass with the spacer. bar contained inside the double-glazed unit.

Product Code
For manufacturing purposes only – indicates the range to be used.


RCM Reinforcement
‘Re-cycled material’ reinforcement which is made from recycled uPVC off-cuts.

Restrictor Stays or Restrictors
An additional feature that can be fitted to a window frame to control/prevent the window opening too wide and are fitted for safety purposes.


Sash box
Original frame or traditional sash windows, which contain weights needed to operate the windows.

Side Opener
Opening section of a casement window where the hinges are located on the top and bottom of the sash and open to the side.

Timber of the same type throughout – i.e. not veneered.

The bar which determines the width between the two panes of glass in the double-glazed unit and runs around the internal perimeter of the unit.

Stops (in reference to windows)
Are additions to the sash window frame to control/prevent the window over-opening for safety purposes.

Stops (in reference to doors)
A term to describe exterior timbers or uPVC, used to finish doors.


Timber Types
Solid hardwoods are used predominantly for internal finishings up to a maximum lengt/width. Above the maximum length/width, we use veneer which is a processed finis and gives the apperance of solid hardwood to prevent warping or bending.

Top Opener
Opening section of a casement window where the hinges are located on the sides of the sash and open at the bottom.

The horizontal bar dividing the window into an upper and lower part.

Glass that has been specially heated and cooled to reinforce the glass and to also limit fall-out of glass in the event of breakage (fragements into very small pieces which don’t have sharp edges).


Unplasticised Poly Vinyl Chloride – the material the frames are made from.


Processed finish which gives the apperance of solid hardwood.


Window Energy 
A guide to the performance of your windows. The rating system (WER) is based on a scale of A-G, A-rated windows being the most energy-efficient.