Double Glazing Glossary

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Glossary

A
Acoustic insulation Relates to the materials used to make a building Soundproof.
A-G ratings British Fenestration Ratings Council (BFRC) energy ratings help inform customers about the relative energy efficiency of particular consumer products. Windows, like white goods and lightbulbs are rated on an A to G scale. An A-rating indicates the most energy efficient products and G-rating showing the least efficient.
Annealed glass A manufacturing process where it is heated and slowly cooled, designed to release any internal stresses from glass panes that emerge flat, to ensure further processing of the glass post-manufacture.  
Anti-reflective glazing Is a glazing treatment designed to reduce light reflectance and show almost no visual reflection.
Argon gas An inert gas that is used within doubled glazed window cavities for improved thermal efficiency.
Aspect ratio The ratio of the longer side of a glass pane in relation to its shorter side.
Astragal Bars Astragal Bars are different to Georgian bars as they are planted on to the window glazing either internally, and/or externally to give the effect of multiple panes of glass. Whereas Georgian window bars are integral to the window and set inside the sealed units.
B
Bargeboard Another name for a soffit.
BBA The British Board of Agrément (BBA) is a UK body issuing certificates for construction products and systems and providing inspection services in support of their designers and installers.
Beaded  Beaded is a simple decorative round moulding, usually cut into a square edge.
Bevel An angled, but not a right angled sloping or canted surface.
Bevelling The glass manufacture process to create a glass edge that’s finished at a bevel angle.
Bifold door A door system comprising three or more leaf panes which fold back fully upon themselves to create an opening.
BPF The British Plastics Federation (BPF) is the leading trade association for the UK Plastic Industry, with over 400 members and 1200 affiliated members
British Standards A set of best practice standards for UK-based and many Ireland-based manufacturers to adhere to.
Building Regulations Building regs. are the legislation or government codes surrounding building control for new building projects as specified by Acts of Parliament.
Butt hinge Also known as SFS hinge, it allows the full closing of a door or window. Butt hinges stand proud of the door or window surface, attaching to the abutting surface of a door jamb or window.
C
Casement The term used to describe arguably the most popular window design in the UK that’s attached to its frame by two or more hinges, with a sash that is side or top hinged. Casement windows open outwards.
Cavity In a double-glazed unit a spacer bar is normally positioned between two panes of glass, creating a cavity that’s often filled with air. However, for enhanced thermal qualities it is filled with argon.
Cill The protruding lip that directs water away from brickwork at the bottom of an opening, such as window or door.
Chamfered The edges have been removed lengthwise at an angle
Cladding A material that’s applied on top of a window or door frame to prevent any elements of the weather from passing through it.
Co-extruded The process of extruding a PVC-U profile and its gasket simultaneously.
Composite door A robust, secure style of door that looks and feels like a traditional timber door constructed from a combination of GRP Wood & uPVC.
Condensation The process by which gas or vapour transforms into liquid via cooling. Read more about condensation in our blog.
Curtain walling Glazed walling used in large buildings, often several storeys high, usually aluminium-framed wall that’s non-load bearing and filled with glass panes to become an integral part of a building’s envelope.
D
Deadbolt A secure locking system used in modern doors.
Desiccant A drying agent regularly used in the process of manufacturing insulating glass units.
Dovetail A type of joint. One piece has a splayed shape – like a dove’s tail – and fits into the socket or eye of the second piece.
Double glazing A glazed product featuring two panes of glass with a space (filled with gas) between them to improve insulation and reduce noise. 24mm and 28mm are the most common, although can come in others.
Double hung Relates to windows with two movable sashes which operate vertically.
Drilled glass Glass panes that have been pre-drilled ready for fixing and fitting as part of the final manufacture process.
Drip groove A groove cut or moulded in the underside of a door or window sill to prevent rainwater running back to the wall.
E
Eaves The edges of a roof that project beyond the walls.
Edge and end spacing Spacings between fasteners, the edges, and ends of the components that are being joined.
Emissivity The surface characteristic of materials such as glass or aluminium. Low-emissivity products are able to absorb radiation.
Energy absorbance The amount of solar energy absorbed and re-emitted by a glass pane.
Energy transmittance The amount of solar energy flow transferred straight through a glass pane.
Extrusion A product made by the manufacture process of extruding.  Most of the profiles used in PVC-U windows, doors, conservatories and roofline are extruded through the process of pushing PVC pellets to form a solid shape.
F
Fanlights  A fanlight is a window with glazing bars that is placed over another window or doorway that opens like a fan, and is sometimes hinged to a transom.
Façade The front or ‘face’ of a building.
Fascia Fascia is used to create a barrier between the edge of the roof and the outside.
Fascia board A strip that covers the ends of rafters and to which external guttering is fixed.
Fixed When describing a door or a window the word fixed refers to it being non operable or opening.
Fenestration An industry term used to describe the arrangement, positioning and installation of an opening such as a door or window in any type of building.
Fin Also known as a glass mullion, a fin is a vertical glass support to stand between two abutting panes of glass.
Fire resistant glass A glazing specification capable of providing an effective barrier against the passage of toxic gases, smoke and subsequent flames; whilst minimising transmittance of radiated heat.
Fogging See condensation.
French doors Double outward-opening doors that meet in the middle without a mullion, giving a clear unobstructed opening.
French windows As with French Doors except for windows..
G
Gasket The black rubber strip that runs around the pane of glass in a window to create a weatherproof join.
Glazing bars Are a range of profiles that fit to the window
Gothic Is a style of glazing bar
Glazing bead A strip of material – usually metal or wood – used to meet the glazing surround with the fixed position of the glass.
Glazing tape Used to install glass and double-glazed glass units into timber and steel-framed window and door systems.
Groove A long narrow channel. Also see Tongued and grooved.
GRP GRP (Glass Reinforced Plastic) is a composite material made of a plastic reinforced by fine fibres of glass. GRP is an extremely tough material, often used as the outer material on composite doors.
G-value Relates to the solar factor of a glass pane, according to EN 410. Previously shortened to SF or TT.
H
Handing Terminology used to describe the operation of a window or door i.e. left or right-handed.
Head drip Head drips appear at the top of a window and are a means of channelling water away from the front face of the window or door.
Head plate The top horizontal member of a stud partition.
Horns Extended door or window stiles designed to protect the corners from damage while in storage.
Heat soak test An additional glass treatment designed to further improve the structural integrity of panes after heat strengthening, reducing the threat of unprompted breakages.
Heat-formed glass Glass panes which have been formed at the highest possible temperatures, sometimes to create aesthetic effects.
Heat-strengthened glass Glass panes which have been treated to develop a structural resistance to thermal damage. With fracture characteristics akin to that of annealed glass it cannot however be known or used as safety glass.
Hook-lock A type of door lock that throws a hook or multiple hooks into a keep when the door is locked.
I
Injection moulding The manufacturing technique used to make parts from both thermoplastic and thermosetting plastic materials in production. Molten plastic is injected at high pressure into a mould, which is the inverse of the product’s shape. Moulds are made from either steel or aluminium and are precision-machined to create the features of the desired part.
Inline patio door A sliding patio door system where the moving door pane slides in front of the fixed pane.
Interlocking joint Interlocking is a way of jointing timber. Each piece is cut to fit against or into another to prevent displacement and to transfer forces. The joint must either be in compression or pinned or keyed after assembly.
Inner pane The closest glass pane to a building’s interior within a double or triple glazed unit.
Insulating glass Two panes of glass separated by a spacer and sealed hermetically with dead air or gas-filled space between the panes.
Integrity The capabilities of a glass pane to retain its structure in the face of the elements and provide a barrier to severe heat and flames, for instance.
Interlayer The material positioned between glass leaves as part of the laminating process. It is typically a resin, PVB or intumescent material.
ISO The International Organisation for Standardisation (ISO) is an international standard-setting body composed of representatives from various national standards organisations. ISO sets standards for manufacturing and environmental processes.
J
Jamb The vertical side member of a door or window frame.
K
Kerf The groove cut by a saw.
Krypton gas An inert gas commonly used to fill small air spaces between glass panes, known as cavities, resulting in improved year-round thermal performance.
K-value The previous name used in the European industry to describe U-values.
L
Lacquered glass The process of depositing and baking highly resistant lacquer onto a specific side of a glass pane to create opaque or coloured glass specifications.
Lambs Tongue is a particular shaped profile that resembles a lambs tongue
Laminated glass The process of laminating two or more sheets of annealed or heat-treated glass, separated by at least one PVB interlayer. The end result is a dependable adhesion between the elements and enhanced security and safety for glazed products.
LAPFAG approval The Local Authority PVC-U Frame Advisory Group (LAPFAG) is made up of a number of Local Authorities, Housing Associations and other public bodies engaged in the production or specification of PVC-U windows. LAPFAG approval helps to satisfy Building Regulations requirements.
Light reflectance The amount of light within the visible spectrum that’s reflected by glass panes.
Light transmittance The amount of light within the visible spectrum that’s transmitted internally by glass panes.
Loading The overarching term used to describe a load exerted onto a structure or elements of it, e.g. wind loads.
Low ‘e’ glass Low ‘e’ stands for low emissivity glass. This glass varies from normal clear glass in that one side has a special metal coating, technically known as a low emissivity coating. Low ‘e’ glass is a type of insulating glass which works by letting in energy from the sun while blocking heat loss from the home.
Low-emissivity glass A glass specification designed to improve thermal performance by blocking a greater percentage of long-wage radiation. Low-emissivity, or Low-E, glass is coated with a thin metal or metallic oxide layer to suppress radiative heat flow.
M
Main frame The section of profile used to construct the outer frame of a window.
Mullion The vertical framing section or support between glass panes. 
Mullion A mullion is the vertical structural element which divides adjacent window units.
Mitre Two pieces forming an angle, or a joint formed between two pieces of wood by cutting bevels of equal angles at the ends of each piece.
Mortise A recess or hole, formed in one piece to receive a projection or tenon on the end of another piece.
Movement The swelling and shrinkage of wood as a result of changing moisture content. Movement in length is always negligible. Movement parallel with the growth rings is greater than at right angles to them. The degree of movement varies between species.
Mullion A vertical dividing member of a window frame.
Muntin A central vertical member of a panel door.
Multi-point locking system A combination of standard multiple point locking mechanisms designed to offer improved security and performance for door and window systems.
N
Non-insulating glass Typically single pane fire-resistant glass.
O
Obscure glass Most commonly used in living areas requiring privacy, obscure glazing is created by running molten glass through specialist rollers, patterning the glass to obscure views both externally and internally. 
Opacified Glass panes which have been made wholly non-transparent by being painted or fully enamelled on either side.
Outer frame An alternative term for the main frame of a window system.
Outer pane The closest glass pane to a building’s exterior within a double or triple glazed unit. 
Ovolo Is a rounded convex moulding
P
Part F Ventilation – Building Regulations. Part F sets out how much ventilation a building must have. Its impact on windows is often the addition of trickle vents.
Part L Conservation of Fuel and Power – Building Regulations. Part L sets the thermal efficiency standards that buildings must comply with. All windows must now meet the standards set out in Part L.
Part M Access to and use of Buildings – Building Regulations. Part M stipulates parameters for the width of front doors and the height of door thresholds, ensuring that people with reduced mobility can easily access buildings. Eurocell Part M compliant thresholds have been designed to offer easy wheelchair access.
PAS 23/24 PAS 23 – General performance of doors / PAS 24 – Enhanced security. PAS23/24 are accreditations that test the performance and security of doors.
Patent glazing A type of glazing system, used typically in overhead glazing, that is non-load bearing. 
Patterned glass A textured glazing specification created by specialist rollers onto molten glass, embossing a specific pattern on one side of the pane whilst keeping the other side smooth. 
Pencil Round  Is a subtle edging profile
Photovoltaic glass A specialist glass specification featuring integrated solar cells, designed to convert absorbed solar energy into electricity.
Pilkington Activ Pilkington Activ™ is self-cleaning glass. In a dual-action process, organic dirt is broken down by daylight and is then washed away by rain, thus making it easier to keep clean.
Polyvinyl Butryral (PVB) The plastic interlayer used between glass leaves in the process of laminating glass to provide the best possible adhesion of materials and subsequently enhance its safety characteristics. 
PVC-U Polyvinyl Chloride – Unplasticised. The rigid plastic used to manufacture Eurocell windows and doors. PVC-U provides low maintenance coupled with long life. The term PVC-U is often misunderstood. Mis-spellings include PVC, PVC-U, U-PVC, UPVC, PVCu and uPVC. PVC-U is sometimes also referred to as just plastic, e.g. plastic windows.
PVC-Ue Polyvinyl Chloride – Unplasticised expanded. Often referred to as foam products. PVC-Ue is used to manufacture many Eurocell roofline products. PVC-Ue has a hard external finish and a slightly less dense core than PVC-U.
R
Rake The trimming of the first compound application used to seal glass panes prior to the use of additional sealants. 
Rebate The area of the glass framework which forms an angle into which the glass is positioned and held in place. 
Reflective coating The metallic or metal oxide coating used to increase the percentage of light and heat reflected by glass panes.
Resin laminate Resin interlayers can be used in the lamination process of two or more panes of glass, in the same way as plastic (PVB) interlayers. 
R-value The level of resistance any material has to heat flow. The higher the number the better its insulating properties. 
Rebated The edge has been cut to form a step, usually as part of a joint.
Reveal The vertical side of an opening in a wall.
S
Safety glass Glass can only be labelled safety glass once it has passed a British Standards impact test (BS 6206: 1981) and must not break or be capable of breaking safely. 
Sash The opening portion of a window.
Sash A type of window or the opening part of a window.
Secured by Design Secured by Design (SBD) is the UK Police flagship initiative supporting the principles of “designing out crime”. Windows and doors that carry SBD approval have been assessed to provide a high degree of resistance to break-ins.
Self-cleaning glass A glass specification designed to break down organic dirt and reduce the adherence of mineral materials over time. A photocatalytic and hydrophilic coating is applied to help glass panes stay cleaner and clearer for longer. 
Self-cleaning glass Glass that uses a dual-action process in which organic dirt is broken down by daylight and is then washed away by rain, thus making it easier to keep clean. Pilkington Activ and St Gobain Bio-clean are brand names for this type of glass.
Sight line The perimeter of the opening that admits daylight into living and work areas. 
Silicone seal Silicone seals are used to fill edges of double-glazed units that are unframed and subsequently exposed to direct sunlight, improving their resistance to UV rays. 
Sill An alternative spelling of cill.
Sill The lowest horizontal member of a stud partition or the lowest horizontal member of a door or window frame.
Soffit The underside of a part of a building such as the eaves or archway.
Stile A vertical side member of a door or window sash.
Stud partition An interior timber-framed dividing wall.
Stud A vertical member of a timber-framed wall.
Soffit Part of the roofline system on a house that seals the house from the elements, between the tiles and the brickwork. Soffit is the horizontal part that runs from the fascia back to the house wall.
Solar control glass A glass specification designed to prevent excessive heat gain for interiors. Panes are coated with a microscopically-thin material to absorb and reflect solar energy. 
Solar heat gain The amount of heat radiated into interiors via a glazed surface. Read more about Heat Loss & Heat Gain here
Sound reduction index A measure of a material’s sound insulating properties within a specific frequency band. Read more about Sound Reduction Index here
Spacer bar These are positioned along all edges of double-glazed units, separating the two panes of glass to create a cavity. 
St Gobain Bio-clean St Gobain’s brand of self-cleaning glass. In a dual-action process organic dirt is broken down by daylight and is then washed away by rain, making windows easier to keep clean.
T
Textured glass See patterned glass. 
Thermal break An area between the inner and outer parts of a glass frame filled with an isolating material of low thermal conductivity to minimise the rate of external heat loss via the frame. 
Thermal break A way of stopping heat or cold transfer between two surfaces. In windows, thermal breaks are often used within the double glazed unit – see warm edge spacer.
Thermally toughened glass Glass panes which have been exposed to a controlled cooling and heating process, with the aim of improving its resistance to mechanical and thermal stress, subsequently enhancing its safe-breakage characteristics. 
Tilt and turn A window system that opens inwardly in two ways. Tilt and turn windows swing completely inwards allowing for easy cleaning. They also tilt at the top to provide good ventilation without leaving the window fully open.
Tinted interlayer A coloured sheet of resin or plastic that binds together two or more panes of glass. 
Toplight A window above another window or door (see glossary entry fanlight)
Total transmittance The amount of solar radiant heat energy transmitted via glass panes, usually attributed in a percentage.
Transom A transom is the horizontal structural element that divides adjacent window units.
Trickle vent A ventilation system built into the top of the window frame.
Transom A horizontal dividing member of a window frame.
Trickle Vent An integrated ventilator within the head of the frame
U
Uniformly distributed load Pressures exerted evenly across a glass pane, e.g. wind load.
UV transmittance The total percentage of solar energy transmitted by glass panes in the form of UV radiation. 
U-value The measure of the rate of heat loss via a building component, such as a window or door system. U-values are normally expressed as W/m²K. 
U-value A measure of heat loss. The lower the U value, the more energy efficient the window.
U-value The u-value is a measure of how easily heat can pass through the materials that make the door or window
uPVC  the abbreviation for Unplasticised Poly Vinyl Chloride
V
Vertical glazing Glazed structures that are either true vertical or within 15-degrees either side of true vertical. 
Vertical slider A window in the style of a traditional vertical-sliding sash window. Eurocell PVC-U sliding sash windows allow both the top and bottom frames to slide freely. The frames also tilt inwards for ease of cleaning.
Vision area The area of a glazed pane which allows an individual to view externally from the interior.
W
Warm edge spacer A new innovation that replaces the aluminium spacer. Used to separate the two panes of glass in a double-glazed unit with a spacer made of a different material (often plastic) that transmits less heat. This makes the window more energy efficient.
Warm-edge The concept of minimising the heat conductive capabilities of double-glazed frameworks by replacing conventional aluminium cavity spacebars with thermally insulating cavity spacers. 
Weathertight Hermetically-sealed windows or doors to prevent the entry of water and air into structures.