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The GGF Glossary
The Glass and Glazing Industry has thousands of products and components as well as companies. Due to its size and diverse nature, it’s also full of jargon and terminology that quite often varies from region to region, country to country, sector to sector and even in some companies from colleague to colleague.
The GGF Glossary is here to help anyone who needs help in understanding it all. It is by no means exhaustive and the GGF is aiming to update this page regularly. If you have and addition or feel something is missing then please contact the GGF and we’ll include it in the GGF Glossary.
| Term | Definition |
| Acoustic Glass : | Glass that has been treated to improve it’s soundproofing qualities |
| Annealed Glass : | Annealing is a process of slowly cooling hot glass after it’s been formed, to relieve residual internal stresses that could cause breakage during manufacture. Annealing glass improves it’s durability |
| Approved Documents : | The Ministry of Housing, Communities and Local Government publishes guidance called ‘Approved Documents’ on ways to meet building regulations. These contain: – general guidance on the performance expected of materials and building work in order to comply with the building regulations – practical examples and solutions on how to achieve compliance for some of the more common building situations |
| Argon gas : | Double and triple glazed windows, commonly have argon gas between the panes to improve insulation and soundproofing. Argon gas is put into the glazing units because it is denser than air and therefore has greater insulating values than air. |
| Astrigal bars : | These are thin wooden moudlings placed on glass to create a period look. They are often used to create the traditional Georgian window look. |
| Awning windows : | These are casement windows that are hinged at the top of the frame. |
| Building Regulations : | Building regulations in the United Kingdom are statutory instruments or statutory regulations that seek to ensure that the policies set out in the relevant legislation are carried out. Building regulations approval is required for most building work in the UK. Building regulations that apply across England and Wales are set out in the Building Act 1984 while those that apply across Scotland are set out in the Building (Scotland) Act 2003. |
| British Standards : | British Standards are the standards produced by the BSI Group which is incorporated under a royal charter (and which is formally designated as the national standards body (NSB) for the UK). The BSI Group produces British Standards under the authority of the charter with the key objective being to set up national standards of quality for goods and services. |
| Casement window : | A casement is a window that is attached to its frame by one or more hinges at the side. They are used singly or in pairs within a common frame, in which case they are hinged on the outside. Casement windows are often held open using a casement stay. Windows hinged at the top are referred to as awning windows, and ones hinged at the bottom are called hoppers. |
| Construction Products Regulation : | Often abbreviated to CPR, the Construction Products Regulation was started in 2013 under the EU but was fully integrated into UK legislation in 2019. This guidance is about placing construction products on the GB market. The GB market refers to England, Wales and Scotland. There is a separate Construction Products Regulation for Northern Ireland. Also in the Republic of Ireland, the CPR is under the EU. The CPR is the legislation that underpins CE Marking and UKCA marking of constrcution products. |
| Composite doors : | Composite doors are made of a selection of materials often including core products such as timber and uPVC. Each material is chosen for its specific properties with the aim being that when combined they will make doors stronger and more durable. |
| Curtain wall : | A curtain wall system is an outer covering of a building in which the outer walls are non-structural, it’s purpose being to keep the weather out and the occupants in. Since the curtain wall is non-structural, it can be made of lightweight materials, thereby reducing construction costs. Glass is commonly used as the curtain wall this offers the advantage of increased natural light. In some cases glass curtain walling can also be used to describe full floor to ceiling glass panels installed in an building’s interior. This is common in office spaces and commercial buildings. |
| Double glazing : | Windows which have two layers of glass with a space between them, designed to reduce loss of heat and exclude noise. |
| Double hung : | Often used to describe a sash window that has two vertical sliding sashes within the larger window frame. Each sliding sash closes/opens a different part of the opening and usually has counterweight on each side. |
| Emergency glazing : | This is a common description when a window or door has been broken or damaged and requires an emergency glazing company to make safe, either by replacement or boarding up until a replacement can be installed. The GGF criteria for emergency glazing companies is that they operate at all times (24/7, every day of the year). |
| Emissivity : | The emissivity of a glass surface is its effectiveness in emitting energy as thermal radiation. Many glass manufacturers reduce emissivity by coating glass, allowing heat to remain inside the house and also to prevent solar heat coming into a property and causing overheating. |
| Energy ratings : | These are used to assess the total energy performance of products such as windows and doors in the same way that household goods like fridges are energy rated using the rainbow label system. A window or door energy rating will not only measure the total energy loss, as a U-value does, but also the energy gain and the air leakage through the window or door. In the UK British Fenstration Rating Council are the leading company when it comes to window and door energy ratings. |
| Fabrication : | Fabrication is the manufacturing process of cutting and assembling the window profiles (frames) together and adding hardware (handles, hinges, locks) along with weatherseals and gaskets to make a finished window (or door) |
| Fan lights : | A fan light is a glazed opening above a doorframe or above the lintel in a doorframe. It is usually designed to allow natural light into a hallway or darker area of a building. |
| Fenestration : | This is the process of positioning, installing and fixing a window, door or skylight in an opening in any type of building. |
| Fire-resistant glazing : | Fire Rated Glass (also known as Fire Resistant Glass) is specialist glass that has been proven to provide a period protection against fire during a Fire Resistance Test. Fire resistant glass is used in Fire Resistant Glazing systems (with special fire resistant seals and components). Fire resistant glazing systems will only work to maximum performance if installed correctly. Certain types of fire rated glass will also provide a degree of protection (insulation) against the heat of a fire. |
| Float glass | Float glass is a sheet of glass made by floating molten glass on a bed of molten metal, typically tin, although lead and other various low-melting-point alloys have been used in this process. This method gives the sheet uniform thickness and very flat surfaces. Float glass is the most commonly used glass in modern glazing (windows/doors/conservatories and curtain walling) |
| Glazier : | A tradesman responsible for cutting, installing, and removing glass. They also refer to blueprints to figure out the size, shape, and location of the glass in the building. Glaziers may work with glass in various surfaces and settings, such as cutting and installing windows, doors, shower doors, skylights, storefronts, display cases, mirrors, facades, interior walls, ceilings, and tabletops. |
| Heat soaking : | Heat soaking. The process involves placing the tempered glass inside a chamber and raising the temperature to approximately 290ºC to accelerate nickel sulfide expansion. The process reduces the risk of spontaneous breakage. |
| Heritage windows : | A heritage window is a type of window that has been manufactured specifically to be installed in a heritage building or building within a conservation area. These type of windows are made with modern materials and used as replica or close to replica replacements for the original windows in historic (usually 100 years or older) buildings |
| Insulating Glass Unit (IGU) : | An insulating glass unit (IGU) consists of two or more glass panes separated by a vacuum or gas-filled space to reduce heat transfer in and out of a building. A window with insulating glass is commonly known as double glazing or a double-paned window, triple glazing or a triple-paned window, or even quadruple glazing or a quadruple-paned window, depending upon how many panes of glass are used in its construction. IGUs are often referred to as “sealed units”. |
| Krypton gas : | An inert gas commonly used to fill small air spaces (cavities) between glass panes, resulting in improved year-round thermal performance. Krypton gas is sometimes mixed with Argon gas to fill the vacuum between glass panes in the production of insulated glass units. |
| Laminated Glass : | This type of safety glass holds together when shattered. In the event of breaking, it is held in place by an interlayer, typically of polyvinyl butyral (PVB), ethylene-vinyl acetate (EVA), or Thermoplastic Polyurethane (TPU), between its two or more layers of glass. The interlayer keeps the layers of glass bonded even when broken, and its high strength prevents the glass from breaking up into large sharp pieces. This produces a characteristic “spider web” cracking pattern when the impact is not enough to completely pierce the glass. |
| Lantern (roof lantern) : | Architectural lanterns are part of a larger roof and provide natural light into the space or room below. In relation to glass and glazing these are products that have a similar affect as skylights (roof windows) |
| Lightwell : | a lightwell, sky-well, or air shaft is an unroofed external space provided within a large building to allow light and air to reach what would otherwise be a dark or unventilated area. Lightwells may be lined with glazed bricks to increase the reflection of sunlight within the space |
| Low E Glass : | Low E stands for Low Emissivity. This is where glass has been treated to reduced energy being emitted from a building or into a building through panes of glass. |
| Mullion | A mullion is a vertical element that forms a division between units of a window or screen, or is used decoratively. When dividing adjacent window units its primary purpose is a rigid support to the glazing of the window. Its secondary purpose is to provide structural support to an arch or lintel above the window opening. Horizontal elements separating the head of a door from a window above are both a head jamb and horizontal mullion and are called transoms. |
| Processors (Glass) | Companies that buy flat glass and then put it through a process to make it perform differently. For example, to make it toughened glass through thermally heating.) |
| Profiles | These are the lengths of framing created by systems houses and framing manufacturers and are supplied to fabricators to trim and develop into window frames. |
| R-value : | the R-value is the term used for thermal resistance in a material. It is a measure of how well a two-dimensional barrier, such as a layer of insulation, a window or a complete wall or ceiling, resists the conductive flow of heat. R-value is the temperature difference per unit of heat flux needed to sustain one unit heat flux between the warmer surface and colder surface of a barrier under steady-state conditions. |
| Rooflight : | A window built into a roof and sometimes referred to as a sky light. These are usually installed to increase natural light into an area (such as a loft) where there may not be much natural daylight. |
| Roofline : | This is a generic description for the products that are installed at the edges of roofs and include fascia boards, soffits, bargeboards, antefixes and cladding that forms the frontage immediately below the roof and the eaves of many homes and building. |
| Sash windows : | A sash window or hung sash window is made of one or more movable panels, or “sashes”. The individual sashes are traditionally paned windows but can now contain an individual insulated glass unit to create a double glazed sash window. |
| Security glass : | This is a specialist type of glass that prevents easy breakage and makes it difficult for burglars or intruders to enter a property. Security glass can be toughened glass (sometimes known as tempered glass), laminated glass or wire mesh glass (glass with wire mesh inside sometimes known as Georgian wire glass – not so common today). |
| Secondary glazing : | This is a glazing system that is installed inside a property when there are restrictions to replace the exterior windows. Secondary glazing often installed in historic buildings and is fixed to the sill inside the building. It |
| Self-cleaning glass : | Self-cleaning glass is a specific type of glass with a coated external surface that keeps itself free of dirt and grime. The field of self-cleaning coatings on glass is divided into two categories: hydrophobic and hydrophyllic. These two types of coating both clean themselves through the action of water, the former by rolling droplets and the latter by sheeting water that carries away dirt. Hydrophilic coatings based on titania (titanium dioxide), however, have an additional property: they can chemically break down absorbed dirt in sunlight. This is often an option for hard to access windows. |
| Sight line : | The perimeter of a window opening that admits daylight into living and work areas. |
| Single glazing : | A window that has one pane of glass. This type of glazing is usually found in older windows and is the least energy efficient glazing option. |
| Skylights : | A description often used for roof windows or rooflights |
| Solar gain : | Solar gain (also known as solar heat gain or passive solar gain) is the increase in thermal energy in a building as the glass (in a window) absorbs solar radiation via sunlight. This can cause overheating in a building. |
| Spacer bar : | A spacer bar is the thin hollow aluminium frame that separates the two glass panes in a double glazed window. The spacer bar is bonded to the glass panes via a primary and secondary seal, creating an airtight cavity enabling it to be filled with air or gas to reduce heat and sound transfer. |
| Tilt and turn : | Tilt and turn windows can be opened fully like a casement window (inwards) or they can be tilted from the bottom so that the top of the window is angled into the room, giving a smaller opening for ventilation. The tilted opening also has the added benefit of increased security and safety as no one can fit through the gap. |
| Trickle ventilator : | A trickle ventilator (sometimes called trickle vent) is a very small opening in a window that allows small amounts of ventilation in spaces intended to be naturally ventilated when major elements of the design – windows, doors, etc., are otherwise closed. Trickle vents are used extensively in the UK and Europe and are integrated into window frames to provide minimum ventilation requirements for naturally ventilated spaces. |
| Toughened glass : | Tempered or toughened glass is a type of safety glass processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. |
| Triple glazing : | A insulated glass unit or window that has three panes of glass with two spaces (vacuums) separating the panes. The vacuums are usually filled with argon gas to reduce heat loss. Triple glazing can offer great security and can be more effective for thermal performance. |
| UPVC : | UPVC is an abbreviation or Unplasticized PolyVinyl Chloride and is a rigid, chemically resistant form of PVC used for pipework, window frames, and other structures. UPVC is sometimes referred to as PVC-U or plastic or PVC when describing double glazing. |
| U-Value : | U-values measure how effective a material is an insulator. The lower the U-value is, the better the material is as a heat insulator. U-values are generally used to describe the thermal performance glazing/windows. |
| Vertical sliders : | Another name for a double hung sash window |
| Warm edge : | A warm edge spacer is a type of spacer bar used in insulated glazing. It separates the panes of glass in double or triple glazing, or curtain walling and seals off the air cavity between each. Recent warm edge spacers are generally made from plastics, although stainless steel can meet the definition. |
| WER (Window Energy Rating) : | A rating systems led by the British Fenestration Rating Council (BFRC), that reviews the whole energy performance of a window, including all of its components. Ratings can go from highest triple A to lowest F and is presented in the rainbow labelling style often seen in white goods such as refrigerators |
| Window Film : | Window film is a thin laminate film that can be installed to the interior or exterior of glass surfaces in the interior or exterior in homes and buildings. It’s often used to increase privacy, solar control, safety and security or to block out strong sunlight. Window film should be installed by professional service companies to ensure best performance. |
