Glossary of glazing terms

With a passion for providing impeccable customer service that’s matched by the quality of our high-performance windows and doors, we’re driven to help our customers understand all there is to know about our aluminium, timber and composite window and door systems.

To that end, we have put together a comprehensive glossary of glazing terminology that we may use to describe to you our products and processes

A-E      |      F-J      |      K-O      |      P-T      |      U-Z


  • Acoustic insulation
    Minimising the ratio of external noise passing its way through a glazed surface.
  • Annealed glass
    A manufacturing process, designed to release any internal stresses from glass panes to ensure further processing of the glass post-manufacture.
  • Argon gas
    An inert gas that’s used to fill cavities within double-glazed low-emissivity units for improved thermal efficiency.
    Anti-reflective glazing
    A glazing treatment designed to minimise light reflectance and show almost no visual reflection whatsoever.
  • Aspect ratio
    The ratio of the longer side of a glass pane in relation to its shorter side.


  • Bevelling
    The glass manufacture process to create a glass edge that’s finished at a bevel angle.
    Building Regulations
    Legislation surrounding building control as specified by Acts of Parliament.
    British Standards
    A set of best practice standards for UK-based and many Ireland-based manufacturers to adhere to.


  • Cavity
    A spacer bar is normally positioned between two panes of glass in a double-glazed unit, creating a cavity that’s often filled with air. However, it can also be filled with argon for enhanced thermal qualities.
    Casement window
    Arguably the most popular window design in the UK that’s attached to its frame by two or more hinges.
    A material that’s applied on top of a window or door frame to prevent any elements of the weather from passing through it. At Livingwood, we sell aluminium-clad glazing.
    Curtain walling
    An extremely thin, usually aluminium-framed wall that’s non-load bearing and filled with glass panes to become an integral part of a building’s envelope.
    The process by which gas or vapour transforms into liquid via cooling.


  • Double glazing
    A glazed product featuring two panes of glass for thermal and/or acoustic insulation.
    A drying agent regularly used in the process of manufacturing insulating glass units.
    Drilled glass
    Glass panes that have been pre-drilled ready for fixing and fitting as part of the final manufacture process.
    Double hung
    Relates to windows with two movable sashes which operate vertically.


  • Emissivity
    The surface characteristic of a material, such as glass or aluminium. If a surface is capable of absorbing and emitting energy via radiation it is considered to be low-emissivity, largely thanks to coatings applied to minimise the normal emissivity of standard glass panes.
    Energy absorbance
    The amount of solar energy absorbed and re-emitted externally and inside a property by a glass pane.
    Energy transmittance
    The amount of solar energy flow transferred straight through a glass pane.
    A product made by the manufacture process of extruding. This includes the aluminium cladding used on the exterior of clad window and door systems.


  • Façade
    The front or ‘face’ of a building.

  • Fin
    Also known as a glass mullion, a fin is a vertical glass support to stand between two abutting panes of glass.

  • Fenestration
    An industry term used to describe the positioning and installation of a window in any type of building.

  • 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
    Occurs when moist air comes into contact with cooler drier air, also known as condensation.


  • 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.

  • G-value
    Relates to the solar factor of a glass pane, according to EN 410. Previously shortened to SF or TT.


  • 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.

  • Handing
    Terminology used to describe the operation of a window or door i.e. left or right-handed.

  • 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.


    • 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.


  • K-value
    The previous name used in the European industry to describe U-values.

  • 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.


  • 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.

  • 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.

  • 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-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.


  • Mullion
    The vertical framing section or support between glass panes. 
  • Multi-point locking system
    A combination of standard multiple point locking mechanisms designed to offer improved security and performance for door and window systems.


  • Non-insulating glass
    Typically single pane fire-resistant glass.


    • 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. 

  • Outer pane
    The closest glass pane to a building’s exterior within a double or triple glazed unit. 
  • Opacified
    Glass panes which have been made wholly non-transparent by being painted or fully enamelled on either side.


  • 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. 
  • 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. 
  • Photovoltaic glass
    A specialist glass specification featuring integrated solar cells, designed to convert absorbed solar energy into electricity.


  • R-value
    The level of resistance any material has to heat flow. The higher the number the better its insulating properties. 
  • 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. 
  • 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. 
  • Reflective coating
    The metallic or metal oxide coating used to increase the percentage of light and heat reflected by glass panes.


  • 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. 
  • 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. 
  • 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. 
  • 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
  • Spacer bar
    These are positioned along all edges of double-glazed units, separating the two panes of glass to create a cavity. 
  • Sound reduction index
    A measure of a material’s sound insulating properties within a specific frequency band. Read more about Sound Reduction Index here


    • Textured glass
      See patterned glass. 
    • 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. 

  • 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. 
  • Tinted interlayer
    A coloured sheet of resin or plastic that binds together two or more panes of glass. 
  • Total transmittance
    The amount of solar radiant heat energy transmitted via glass panes, usually attributed in a percentage.


  • 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. 
  • UV transmittance
    The total percentage of solar energy transmitted by glass panes in the form of UV radiation. 
  • Uniformly distributed load
    Pressures exerted evenly across a glass pane, e.g. wind load.


  • Vertical glazing
    Glazed structures that are either true vertical or within 15-degrees either side of true vertical. 
  • Vision area
    The area of a glazed pane which allows an individual to view externally from the interior.


  • 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. 
  • Wind load
    The positive or negative force on an external area of a building directly resulting from wind. Typically expressed as N/m². 
  • Window Energy Rating (WER)
    A programme led by the British Fenestration Rating Council (BFRC), designed to review the whole energy performance of a window, including all of its components.
  • Weathertight
    Hermetically-sealed windows or doors to prevent the entry of water and air into structures.

When we bought our lovely old house 8 years ago it was in need of a huge amount of TLC which is quite an understatement, it was always our intention eventually to add a garden room to enable us to enjoy the beautiful view over the parkland even more.

Toby and his team at Livingwood provided us with timber windows and CF68 aluminium bi-fold doors for the new garden room extension, the windows & doors are fantastic quality and the team were extremely helpful through the whole process.

We would thoroughly recommend Livingwood Windows.

Jane & Trevor Smith

New garden room to enjoy our fantastic park views
Read more testimonials