Every industry has its own language. Below is an A to Z glossary of terms so you can understand your installer!

A

A-G energy ratings: Windows are rated on a scale of A to G, with A indicating the most energy efficient glass products. It’s a scale devised by the British Fenestration Ratings Council. Find out more here.

Acid Etching: A decorative process in which the glass surface is treated with hydrofluoric acid to make it smooth and opaque.

Acoustic Glass: Two or more sheets of glass bonded together to provide acoustic insulation for noise reduction.

Air Space (Air Gap): The space in the cavity between the panes of glass in an insulated glass unit.

Annealed Glass: A process in which hot float glass is gently cooled to release internal stresses so it can be further cut and processed after manufacture.

Argon Gas: An odorless, inert, non-toxic which is six times denser than air.  The gas fills the gap between the panes of glazed windows to improve their thermal efficiency by slowing down the energy (temperature) transfer.

Anti-snap locking cylinder: The cylinder of a lock is one of the key components and it's where the key is inserted.  With anti-snap locks, intruders will find it more difficult to force entry because the cylinder is split into two halves, with a snap line in the middle.  If force is applied to the lock, the initial cylinder will snap but the second will be able to stay intact, so your home is protected.

Awning Window: A top-hinged window that swings outward for ventilation.

B

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.

Bead: A moulding or strip placed around a window frame to hold the glass in place by pressure.

Bevelled Edge: Glass edges that have been ground and polished to an angle, refracting light.  Can also be bevelled frames to offer a smooth and sleek style of frame.

Bi-folding door: A door style which opens in a concertina style so that the door panels are able to stack to either the left or right side. They're offered in external and internal use. You can choose from a range of configurations to fit any desired space in your home.

Butyl: A synthetic rubber used to seal insulated glass units to make them air and water-tight.

C

Cames: The narrow strips (usually lead, zinc or copper) which hold together the pieces of glass in stained glass windows.

Casement: The part of a window that opens is called casement.  The casement is usually secured by a hinge fixed to the side (can be top or bottom) of the window frame.

Cavity: The space between the panes of glass in a double or triple-glazed unit, usually filled with air, or with argon gas for enhanced thermal performance.

Composite Frame:  A frame consisting of two or more materials, eg an interior wood element with an exterior aluminium element.

Condensation:  The accumulation of water vapours or droplets as the result of warm, moist air coming in contact with a cold surface and cooling to its dew point temperature. Condensation may occur when a cold window glass or frame is exposed to humid indoor air.  Low-conductivity, insulated glass and warm-edge spacers reduce condensation.

Conduction:  Heat transfer through a solid material by contact of one molecule with the next. Heat flows from a higher temperature area to a lower temperature one.

Cullet: Waste broken glass that is recycled and used to make new glass.

D

Dessicant: A porous substance which is used to absorb moisture inside the sealed space of an insulating glass unit.

Double Glazing: Using two panes of glass, with a cavity in-between, in a window to increase energy efficiency and improve sound-proofing.

Dormer:  A space which protrudes from the roof, usually including one or more windows. Dormers can be hipped, gable or flat roof style.

Dry Glazing: A method of securing glass in a window frame with a gasket without using a glazing compound.

E

Electrochromic glass (smart glass): Electronically tintable window glass which can be controlled by a building’s occupants to clear and darken, enabling the management of light and glare without cutting out outdoor views.

Emissivity: A measure of how efficiently a surface – such as glass – radiates heat. The emissivity of glass can be regulated by coatings.

Extrusion   Aluminium or uPVC profiles used in a window. An extrusion is produced by pushing material through a die with an aperture of the shape of the section.

F

Fenestration: A term that describes any opening in a building, including windows, doors and skylights that require a window or door in the structure.

Fixed Light window: These are usually fitted to enhance the views from the window and allow more natural light to enter. Fixed lights can’t be opened so they can’t add extra ventilation.

Fire resistant glass: A type of glass that provides a barrier against the transmission of flames, smoke and gases for a longer period than normal glass.

Float Glass: Sheets of glass made by floating molten glass on a bed of melted metal (usually tin). The glass is cooled very slowly in an oven called a lehr in a process called annealing, which relieves the internal stresses.

Frame: That part of a window assembly surrounding the sashes or fixed glazing.

French Door:  A particular design of swing door, all or a large part consisting of divided glass panes.  Usually two glazed door panels which can be opened either outwards or inward.

G

G Value: The G Value of glass is a measure of how well the glass transmits heat from the sun (solar energy). It is usually notated as a percentage.  The more layers of glass there are, and/or the more coatings there are on the glass, the more there is to block the sun’s heat (infrared radiation) from penetrating inside a building, so the lower the G value the better.

Gaskets: Shaped extruded rubber parts used for securing and positioning glass into a frame.  It is pliable, flexible continuous strip of material used to affect a watertight seal between a sash and frame much like the seal around a refrigerator door.

Glazing: The act of installing glass into a frame.

Glazing Bars: These bars are fitted onto the glazing panes to hold it in place in the window frame. They are usually designed in a grid to replicate the heritage style.

Glazing bead: Metal or wood strips used to fix the glass into a frame.

Glazing tape: A double-sided tape used for installing single pane glass and double-glazed units into timber or steel windows and doors.

H

Hardware:  Window or door hardware serves a primary role of allowing the system to function. Hardware pieces include hinges and sash fasteners.

Head:  The top frame of a window below the lintel.

I

IGU - Insulated Glass Unit:  Two or more plates of glass separated by a spacer and hermetically sealed at the glass edges.

Integral blinds:  These are blinds which are fitted within the glass panes of windows or doors.  As they aren't exposed, integral blinds won't need any upkeep and will continue to look like new whilst enabling you to control the amount of natural light which enters your room

Inner pane: The pane of a double or triple-glazed unit which faces to the inside of the property.

Interlayer: The material used to bond leaves of glass together to make laminated glass.

J

Jamb:  Vertical sections of the main frame.

L

Laminated Glass: Two or more glass sheets bonded together with interlayers of plastic or resin material. This provides glass that is held together and doesn’t fragment when broken.

Leaded Glass: Glass pieces joined together with lead strips (known as cames) which is soldered together to form a composite pane.

Low Emission Glass (Low-E glass): Clear glass with an extremely thin coating of metal oxide, which allows heat and light to pass through it into a building, but blocks the heat from radiating out of the room, reducing heat loss and saving energy.

Louvre windows:  Louvre windows are made up of a series of parallel pieces of glazing that are hung on centre pivots positioned at intervals down the vertical jambs that allow them to open and close using a crank or lever. One huge downside with louvre windows is that they do not have very good insulating properties.

Lintel   A horizontal framing member placed across the top of the rough opening of a window or door opening to prevent the weight of the wall or roof from resting on the window frame.

M

Manifestation: Markings (a sticker, or an etching) applied to expanses of glass to make it visible and therefore avoid accidents.

Main Frame:  The head, sill and jambs sections of a window.

Mullion: A vertical division between parts of a window – it could be decorative or supportive (as part of the frame).

Multi-point locking: Multi-point locks secure the door to the frame at several points to provide greater levels of home security.

O

Obscure Glass: Glass deliberately created with an uneven surface designed to diffuse light and offer privacy by obscuring the view inside and out.

Opacified Glass: Glass which has been enamelled or painted on one side to render it non-transparent.

Outer Pane: The pane of a double-glazed unit which is on the outside of a building.

P

Pane:  A sheet of glass for glazing a window.

PAS 24:  PAS 24 is a standard of testing to measure the security performance of windows and doorsets to ensure they can resist a level of attack from an opportunist burglar.

Patio Door:  This is a glass door style which uses large panes of glass in each door panel, letting in lots of natural light.  The glass door slides open to either the left or right, so they're ideal for saving space as they don't require any additional floorspace to open outwards like a standard door.

Patterned Glass: Glass that is textured by having a pattern embossed on one side of the hot glass during the manufacturing process.

Passivhaus standard:  The Passivhaus standard is an international energy performance standard for buildings.  The standard aims to reduce the requirement for space heating and cooling through a number of factors, including larger insulation depths and using the sun's heat to warm the house.

Photovoltaic (PV) glass: Using the same principle as solar panels (although it is transparent) this glass has integrated solar cells which convert energy into electricity.

Pivot windows: Windows with a central hinge that make it possible to rotate the window through 180º so that the exterior pane is facing inwards. This is very practical when washing windows.

Plate Glass: Largely overtaken by float glass (which is superior for most applications), plate glass is a soda-lime-silica glass created by rolling hot glass into a plate, subsequently being ground and polished smooth. This was the original way of producing window glass.

Polyamide break:  This is a plastic barrier which is fitted between the inside and outside of an aluminium door frame.  It's purpose is to enhance the thermal performance of the door as it stops the warmth from escaping and the draughts from entering

Polyvinyl Butryral (PVB): The commonly used plastic for the interlayer between glass leaves in laminated glass, preventing it from fragmenting when broken.

Powder coating:  is a type of coating that is applied as a free-flowing, dry powder. Unlike conventional liquid paint which is delivered via an evaporating solvent, powder coating is typically applied electrostatically and then cured under heat or with ultraviolet light.

R

RAL Colours:  This is a colour matching system used in Europe for paint and coatings.     Each of the 200+ RAL colours has its own unique RAL code.

Rebate: The recess in a frame into which a glass pane is placed and secured.

Resin laminate: Laminated glass assembled by using a resin interlayer instead of PVB.

S

Sash:  The part of the window which contains the glass.

Safety Glass: Glass that is specifically designed to be less likely to break, and therefore less likely to cause an injury if it does break.  There are two types of safety glass – laminated glass and tempered glass. Safety glass is mandatory in some situations.  Usually French, patio and bi-fold doors will use safety glass.

Sandblasting: Firing fine sand at glass to create a frosted, translucent glass appearance.

Self-cleaning glass: Glass treated with an ultra-thin coating of titanium dioxide, resulting in the surface repelling water and reducing the adherence of dirt particles, which run off the surface without streaking.

Sill: The horizontal, bottom section of the main frame, inside and/or out.  The external sill is usually angled and projecting beyond the line of the wall to allow rainwater to run off

Sidelights:  These are narrow glass panes which tend to be found alongside a front door for a decorative purpose. They are most commonly designed using obscured glass to let some natural light in, whilst still maintaining privacy.

Skylight:  These are windows fitted flush into the roof. The brand name ‘Velux’ has become associated with opening domestic rooflights.  Skylights or Velux windows are traditionally the “go-to” option for anyone that wants to get some natural day light into a loft or roof space or even into an extension or existing flat roof.  Skylights, velux windows and rooflights are available in a huge range of sizes, shapes and designs to suit any taste or requirement.

Shootbolt locking system:  The system has three main elements; the central gearbox and two shootbolt rods which slot into the gearbox. This locking system can be fitted to windows or doors and is commonly locked into the surrounding frame at either the top or bottom. The central gearbox has small holes which the shootbolt rods slot into. When the system is locked, the shootbolt rods connect and move vertically into the top and bottom of the frame, securing it in place.

Spacer Bar: A spacing bar along the edges of a each gazed unit, filled with dessicant.  The spacer bar is designed to maintain a unform width between the panes of glass and create a cavity.

T

Tempered/Toughened Glass: This is a type of safety glass processed to increase its strength by controlled thermal or chemical treatments. It is much stronger than normal glass and resistant to breakage, but if it does break it shatters into small granular pieces rather than sharp shards.

Thermal break barriers:  Aluminium window and door frames have thermally broken frames. They use plastic barriers which are fitted to the inside and outside of the frame to break up any currents of airflow, whilst stopping any heat from escaping from the rooms. This significantly improves the thermal performance of aluminium products.

Threshold: It's a sloped element which runs along the bottom of a doorway to separate the inside and outside of the property.  It seals the underneath of a door to stop any rain or elements from getting into your home.  Low thresholds can be fitted in a number of sizes to reduce the height of a step.  They're commonly found in households where people with mobility issues or young children live.

Tilt & Turn Windows:  Windows with fittings that make it possible to tilt the window inwards from one edge or to open inwards from one side.  Many can tilt & turn so the that the exterior pane is facing inwards. This is very practical when washing windows.

Transmittance:  The percentage of radiation that can pass through glazing. Transmittance can be defined for different types of light or energy, e.g. visible light transmittance, UV transmittance or total solar energy transmittance

Transom: A horizontal division in a window.

Trickle Vents: A small opening at the top of a window to allow for ventilation.

Triple Glazing:  Glazing that incorporates three panes of glass, enclosing two separate air spaces.

U

U Value: A measure of the rate of heat loss through a building component – such as a window or a solid wall. It is expressed in W/m2k (watts per square metre per degree Kelvin). The lower the U value of a product the better.

uPVC:  Unplasticized Polyvinyl Chloride (uPVC) is the plastic material used for plastic window and door frames.

V

Vent light:  Is a small opening window at the top of a window or door.

Visible Light Transmittance:  The percentage of light that is transmitted through glass in the visible light spectrum (380 to 720 nanometers). The higher the number the higher the percentage of visible light transmitted through a glazed window or door.

W

Warm Edge: This is a type of technology relating to the type of spacers used in a double or triple glazed unit that conduct less heat or cold than standard units.

Warranty: A product warranty is a written guarantee that is offered with window and door products.  A warranty may cover the cost to repair or replace a particular product within a specific period of time.

Weather Seal:  To keep the elements out of your property, fitted around doors and windows.

WEER: The Window Energy Rating (WER) scale illustrates the energy efficiency performance of a window, ranging from G to A+. A+ energy rated windows provide the highest levels of energy efficiency performances.

Weep Slots:  Slots or holes in the sill (bottom) member of the sash frame that allows water to escape.

Wind Load:  The wind pressure in Pascals that the window has to meet according to location and exposure.