Double Glazing Glossary

Here's a list of some of the more technical terms that are used in the double glazing industry. If you're researching about new windows, doors or conservatories, it's likely that you'll come across some of these. If you still don't understand what is meant or would like further clarification, please get in contact with us and one of our specialist experts will be able to advise and help you out.

Astragal Bars

Astragal bars are fitted to the windowpane on both the outside and inside in a grid pattern. They are used to add a heritage decorative touch. Traditional windows used to use several panes of glass for one window which were connected with slim bars, however nowadays we use just a single pane of glass. Therefore this design is just for aesthetic reasons on modern windows.

Bevelled Frames

Also known as chamfered frames, they have a flat profile. Because of their more sleek appearance, they are commonly chosen for new-builds and modern homes.

Bottom Hung Window

A window that is hinged at the bottom of the frame. Sliding sash windows commonly have this functionality.

Bottom Rail

The bar that sits across the bottom of the window frame.

Casement Window

The most commonly found window style, a casement window usually opens outwards from either the left or right of the frame. We offer uPVC, timber and aluminium casement windows.

Centre Hinge Window

The window sashes pivot on the central hinge. They're usually fully reversible for larger openings and easier cleaning.


The very lowest ledge that makes up the bottom of the window frame.

Double Glazing

It uses two panes of glass that surround an argon gas-filled space, to reduce energy wastage and external noises from entering the room. Its advanced design is able to break up currents of airflow to retain the heat inside and keep the cold elements out, keeping your home energy efficient. You'll benefit from reduced energy bills and a lower carbon footprint with modern double glazing.

Double Hung

This is a sliding sash window style that has two movable sashes, so either the top or bottom sash can be opened for ventilation.

Fixed Light Window

A fixed light window is usually installed to enhance further views and increase natural light, rather than for ventilation purposes as it cannot be opened.

Flush Sash Window

A flush sash window is a modern alternative to traditional window styles. The window sash sits flatly within the frame, creating a sleek and elegant aesthetic.

Fully Reversible Window

Fully reversible windows have a unique opening mechanism. They can be opened and tilted 180 degrees, making it much easier to clean the windowpanes from inside.

Georgian Bars

Unlike astragal bars which are applied on top of the glazing, Georgian bars are fitted within the layers of glazing in a grid pattern. They're used to add a heritage touch to new windows.

Glazing Bars

These bars are placed onto the glazing panes, holding it in place within the window frame. They are often designed in a grid pattern, replicating the heritage style.


A measurement to establish how much heat can pass through a window. Lower values mean that the glass has more protection from infrared radiation. Depending on the product, our glass can achieve G-values as low as 0.3.

Head Jamb

The top horizontal bar that makes up the top of the window frame.

Leaded Glass

Found on the window glazing, the metal or wood strips can be designed in many decorative patterns for a heritage appearance.

Low-E Glass

Low-emissivity glass has a thin coating applied to the outside of the glazing panel. It allows heat from the sun to enter the room to warm it up, and when the room reaches a comfortable temperature, it will reflect the rest of the sunrays. This helps to improve energy efficiency and reduce heating bills.

Multi-Chambered Profiles

This design uses several layers of uPVC that surround several separate chambers inside the profile. These window frames are more energy efficient than a standard frame, as the chambers retain the warmth within the home, whilst stopping cold air from entering.


A window mullion is the vertical beam which divides the window into several units. It's primary function is to support the glazing panes.

Ovolo Frames

Olovo window frames have a curved shape. They replicate the period style, making them ideal for older homes and listed properties.

Reinforced Meeting Rail

The meeting rail of a window is the part where the rail of each sash meets one another when the window is closed.


The sash is the section of the window that holds the glass panes and can be moved. It’s fitted inside of the main window frame.

Sash Eye

These are found on vertical sliding windows to assist the unique opening mechanism. A sash eye is designed to fit on the top rail of the bottom sash and assist in lifting them up and down.

Sash Horn

A unique feature found on sliding sash windows, a sash horn prevents the sashes from opening further than they should and becoming jammed. They're usually designed in either a curved or 's' shape to replicate the authentic appearance.

Shootbolt Locking System

A locking system has three main parts, consisting of a central gearbox and two shootbolt rods that fit into the gearbox. They can be fitted as part of a window or door and is usually locked into the surrounding frame at the top or bottom. The gearbox has small cavities which the shootbolt rods slot into. When locked, the shootbolt rods, which are fitted at both ends, connect and drive vertically into the top and bottom of the frame.

Side Hung

This is a window that opens from either the left or right side of the frame.

Single Hung

A single hung window has one sash that can be moved. For example, a sliding sash window has a top sash which cannot be pulled or pushed but the bottom sash can be moved to open the window.

Sliding Sash Window

Sliding sash windows have either one or two sashes which can be moved vertically. Because of their unique opening, they have their own collection of sash hardware and furniture, which enables the functionality as well as adding to the heritage style. They are commonly found on Georgian and Victorian properties.


These are the vertical edges of the window frame.

Tilt & Turn Windows

Tilt and turn windows provide a versatile number of openings. They can either be opened by the top or bottom hinge for a small gap to allow ventilation. Alternatively, they can be opened inwards from either the left or right of the frame for easier cleaning.

Top Hung Windows

Top hung windows open from the top of the window.

Top Rail

The top rail is the horizontal bar that sits across the very top of the frame.


A transom is the horizontal version of a mullion, dividing the window into several parts. It helps the window to stay structurally intact.

Travel Restrictor

Travel restrictors are commonly found on sliding sash windows. They are fitted on the inside of your home on the window sash and restrict how far the window can be opened, making them popular with homeowners who have young children.

Trickle Vents

A trickle vent is a very small opening in a window that allows for small amounts of ventilation.

Triple Glazing

This uses an additional pane of glass to double glazing; the three panes surround argon-gas filled chambers for heightened energy efficiency and noise reduction.

Vertical Jamb

These are the vertical bars that form the sides of the frame.

Warm Edge Spacer Bar

They are placed inside the edge of the glass, keeping the glazing panes apart. This reduces energy wastage and external noises from entering the home. They also reduce the likelihood of condensation forming within the window panes.

Weather Gaskets

A weather gasket, also known as a weather strip, specialises in sealing openings on doors and windows, preventing rain and water from being let in, as well as keeping interior air in.


The Window Energy Ration (WER) scale indicates the energy efficiency of a window, it ranges from G to A+, with A+ being the most efficient.

Anti-Bump Locking Cylinder

Bumping a lock is when someone makes the pins jump above the shear line to gain access, an anti-bump lock has more pins and uses specially made keys to prevent this.

Anti-Snap Locking Cylinder

The cylinder of a lock is one of the main components. Its the part of the door lock where the key is inserted. When the lock is anti-snap, it means intruders will find it more difficult to break an entry by force. This is because the cylinder is split into two, with a snap line in the middle. If force is applied, the first cylinder will snap however the second cylinder will stay intact, protecting your home.

Bi-Fold Door

Bi-fold doors open in a concertina style so that the door panels stack to either the left or right side. They're available in aluminium or timber, and will add a modern touch to any home. They can be installed in a number of configurations to fit any size in your home.

Dog Bolts

Dog bolts are also known as hinge bolts. They are steel pins which are slotted into the side of the door where the hinges are found. When the door is closed, the bolt passes into a slot on the door frame to maximise it's resilience from forced entry.


The Door Set Energy Rating (DSER) is a scale that illustrates the energy efficiency of a door, with E being the lowest and A++ being the most insulating. Dependent on the style and material, many of our doors achieve the top-level ratings.

French Door

French doors comprise of two glazed door panels that can be opened either outwards or inwards. Their simple opening makes it easy to blend the home and garden. We offer uPVC, timber or aluminium French doors in both modern and traditional styles.

GRP Skin

Glass reinforced plastic (GRP) skins are used on the outer of composite doors. The modern material is incredibly weather resistant, reducing the likelihood of scratches, peeling, warping and fading.

Locking Cam Catches

A cam lock is a latch that consists of a cam and base. The cam is a metal plate and is the main component, latching onto the base. The base is the section where the key is inserted. When the key is turned, the cam rotates either 90 or 180 degrees and secures to the base when locked, or releases when unlocked.

Low Threshold

This is a slightly sloped piece which runs along the bottom of a doorway, separating the inside and outside. It provides a seal underneath the door, potentiating any rain or elements from getting into your home. Low thresholds can be installed in a range of sizes, reducing the height of a step. They are popular in households with members who have mobility issues or young children.

Multi-Point Locking

A multi-point lock, as the name suggests, locks at multiple points and bolts the door into the frame, ensuring a high level of security.

Polyamide Break

A plastic barrier that is placed between the inside and outside of an aluminium door to increase its energy efficiency as it stops heat from escaping and cold air from entering.

Safety Glass

Also called toughened glass or tempered glass, it is made using advanced chemical processes and then left to cool to significantly increase its strength. When smashed, it disperses into thousands of tiny pieces. It is used in door styles that incorporate large panes of glass, such as French doors and patio doors.


They are narrow panes of glass usually found alongside a door for a decorative purpose. They tend to use obscured glass to let natural light in, whilst retaining privacy.

Slave Door

They are part of the overall door design but are fixed in place and cannot be opened. Slave doors are commonly found on the side of French doors for a decorative purpose, whilst letting more natural light in.

Sliding Patio Door

A sliding patio door uses large panes of glazing in each door panel, letting in the natural light. The panels slide open sideways so they're ideal for saving space as they don't need any floorspace to open outwards or inwards, like a standard door. They're available in uPVC, aluminium or timber.

Traffic Door

A traffic door can be built into a bi-fold door system on either one or both sides. It functions like a standard door, opening either outwards or inwards. They're ideal for making access in or out of the home easier, when opening the bi-fold system isn't practical all the time.

Clad Over Roof

An old-fashioned replacement roofing system that is made from timber, tiles and plasterboard. It is fitted on top of an existing outperforming conservatory roof, including polycarbonate and glass. However, they are not as high-performance as other roofing solutions. They commonly experience leaks and draughts and won’t keep the conservatory at a comfortable temperature in the different seasons. At T&K we don’t offer clad over roofs due to their poor performances.

Crestings & Finials

Usually found on traditionally styled conservatories, they are placed on the roof of a conservatory. They can be designed in a range of styles, but usually have a long cresting strip of decorative patterns, with a larger spike (finial) at each end. Common styles are Victorian and Gothic designs. The decorative spikes not only enhance the appearance but stop birds from landing on the roof.


Placed on the outside of the roof where the brickwork meets the roof, a decorative cornice protects the extension from the weather elements and hides the guttering. It surrounds the perimeter of the conservatory and can be designed in a range of sizes and styles. They can range from traditionally curved to a flat sleek design.

Double Hipped Conservatory

A double hipped conservatory features a pitched roof on both sides and have a rectangular floorplan. They can be installed in any size to fit both large and smaller homes.

Edwardian Conservatory

Edwardian conservatories are also known as Georgian conservatories. They have a square or rectangular floorplan with a sloped symmetrical roof.

Home Extension

A home extension is a new room or building which is added to an existing property.

Insulated Columns

In comparison to standard brick columns, insulated columns offer 5 times better thermal insulation. It has an insulated core that uses expanded polystyrene and styropor column, which is enclosed with an OSB board. Together this breaks up any currents of air, keeping the warmth inside and the draughts out. Insulated columns are fitted on each corner of the conservatory, and stand from the floor to the roof. You can choose from a range of sizes to add style to the extension.

Internal Downlights

These are integrated spotlights that a placed into an extension’s ceiling for a modern method of lighting the room.

Internal Plastered Soffit System

Structured ceiling panels that are placed inside of the extension on the outer edge of the room. It frames the room, giving a modern appearance, whilst allowing more air to flow to reduce the occurrence of condensation.

Lantern Roofs

This is a roofing system that is formed of angled glazed panels, usually found in the centre of the ceiling to create a centrepiece and add a bespoke appearance. They can be added to any flat roofed extension, including conservatories and orangeries.

Lean To Conservatory

A lean to conservatory has a rectangular floorplan with a sloped roof made of one large panel. It has the name 'lean to' as the roof leans up towards the wall of the main property.


Orangeries originated from the 17th century to grow citrus plants and protect them from the outdoor elements. They are have grown to become a popular home extension that is made using more brickwork than a typical conservatory, offering a bespoke appearance that can incorporate any roof, door and window elements.

P Shaped Conservatory

P shaped conservatories combine the rectangular lean to style with the curved shape of a Victorian style. As they have a larger design, they're ideal for bigger properties or for a new space to be used with two functions, such as a living room and dining room.

Self-Cleaning Glass

The glazing panels are coated with a thin lining that is able to break down debris itself, eliminating any maintenance needs.

Victorian Conservatory

Victorian conservatories are a style that are notable for their pitched roofs which usually comprise of three or five sides, creating a curved appearance.


An Area of Outstanding Natural Beauty (AONB) is used for conserving areas under the Countryside and Rights of Way Act 2000. It can be used by local planning authorities to avoid property owners diminishing areas that are seen to have a significant landscape.

Acoustic Insulation

Acoustic insulation is how well something performs at soundproofing, i.e. making sure sound does not transfer through.


One of the strongest construction materials, aluminium is lightweight, corrosion-resistant and can be recycled. Aluminium windows, doors and conservatories have a unique slimline appearance that can be finished in over 150+ RAL colours. With thermally broken frames, they provide superior energy efficiency.

Anti-Glare Glass

Anti-glare glass is a special kind of glass that prevents any reflection and uncomfortable glare. So when the sun is shining, you’ll still be able to use your conservatory without squinting from the sun.

Anti-Jemmy Bars

These are metal strips which are fitted to the edge of a lock on outward opening windows and doors. Their purpose is to stop the window or door from being forced open.

Argon Gas

Argon gas increases the energy efficiency and performance of s window or door. It is used to fill the space between the panes of glass, slowing the transfer of energy and breaking up the molecular movement of airflow. It is odourless and colourless.


Composite is a material used for doors. It combines dense polyurethane foam and modern uPVC materials in the core, which is coated in a glass reinforced plastic (GRP) skin. Because of its thick core and durable frames, composite doors are highly insulating and secure. Composite is one of the most versatile materials, and we offer 42 colours including several woodgrain effects. With a variety of decorative glass and furniture options, we can achieve both modern and traditional styles.

Conservation Area

A conservation area is an area that is intended to be preserved or enhanced because of its historic interest or special architecture, thus resulting in stricter limitations for home improvements. We offer products that are better suited to such environments, including heritage wood effect windows, traditionally styled front doors and sash windows.

Decorative Glass

Depending on the product and style, you can choose to incorporate decorative glazing to add a unique touch to the appearance. Designs include stained, frosted, leaded, etched, patterned and bevelled. They can all be finished in an array of unique aesthetics, and some have obscured glazing to heighten privacy.

Dual Colour

A design choice that gives homeowners more versatility as the outer and inner of the window frame or door frame and panel can be two different colours.


A fanlight is a small window which is fitted above another window or door. They will let in more natural light, whilst adding a decorative touch to the design.


Window or door furniture includes door handles and letterplates. They’re essential for the functionality but can also add a decorative touch. You can choose from a range of styles and colours to further customise the appearance of the window or door.


Window or door hardware have a primary purpose of allowing the system to function, such as hinges and sash fasteners.

Home Improvement Finance

Home improvement finance options allow homeowners to improve their homes on a payment plan that's suited to their individual requirements. We offer a range of finance options, including buy now pay later and interest free options.

Integral Blinds

This is a blind system that is incorporated within the panes of glass of windows or doors. As they are not exposed, they don’t require any maintenance whilst giving you the flexibility of allowing natural light in when you desire.

Listed Buildings

They are older properties that have special architecture or historic interest that should be protected. This means planning permissions can be restricted to retain the heritage appearance and importance.

Low-Emissivity Glass

Also known as low-e glass, this is a type of energy-efficient glass that is designed to prevent heat escaping through your windows thanks to a microscopic coating applied to it.

Microporous Paint

Microporous paint is applied to timber windows and doors. It's a coating which adds a protective barrier against liquid water from being absorbed. This allows the natural timber elements to breathe to eliminate it from rotting or splitting.

Obscured Glass

This glazing type helps homeowners to retain their privacy whilst letting natural light brighten the room, as you can’t see through the glass.

Passivhaus Standard

The Passivhaus standard is ideal for eco-friendly homeowners looking for a low-energy home as it uses 90% less energy than an average home. It’s not required in the UK, as Building Regulation standards ensure excellent energy efficiency levels. Passivhaus standards are achieved through a range of factors, including heightened insulation depths and using heat from the sun to warm the home.

PAS 24 Accreditation

A PAS 24 accreditation is given to home improvement products that meet certain criteria. This is tested through a number of regulations to examine it's security performance and ensure that it protects from common burglary methods.

Planitherm Glass

Planitherm glass is high-performance glass that have a range of features to increase comfort within the home, such as enhanced security and noise reduction.

Powder Coating

A powder coating is applied to aluminium windows, doors and conservatories. Powder coatings are much more protective than regular paints, eliminating the products from fading, rotting or corroding.

RAL Colours

A colour system that is used across the industry. Each of the 150+ colours has its own RAL code.

Solar Control Glazing

Solar control glazing has an additional coating applied to the glass panes. It ensures that an optimum amount of the sun's heat is let in and deflects the rest from entering the room. This ensures the room is kept cool in the summer and warm in the winter.

Thermal Break Barriers

Our high-quality aluminium frames have thermal break barriers. These are plastic barriers which are slotted within the inner and outer frame to break up currents of air and stop any heat from inside from escaping. This improves the thermal insulation of the aluminium products, minimising energy wastage.


Timber was the original material for windows and doors and is still highly popular today. It offers a natural traditional appearance and texture that will add character to any home. It's incredibly strong, robust and is naturally insulating. We source only sustainably grown timber materials, making it an excellent choice to reduce your home's carbon footprint.


Unplasticized Polyvinyl Chloride (uPVC) is one of the most popular home improvement materials. It's benefited from modern manufacturing techniques that makes it incredibly versatile, durable and low-maintenance. With multi-chambered frames, our uPVC products will improve your home's energy efficiency.


U-values are a measurement that look at how effective a material is as an insulator, the lower the U-value, the better the insulation of the element in question. Depending on the product, our range of windows, doors and conservatories can achieve U-values from 0.8 w/m2K to 1.2 w/m2K.

Visible Light Transmittance

Visible light transmittance (VLT) is the amount of daylight which can be passed through a glazed system. The lower the tint percentage, the less light that can be let into your home.


A product warranty is a written guarantee given to each of our products. It means that we will repair or replace a particular product within a specified time period.

Woodgrain Foils

Woodgrain foils are applied to the outer surface of uPVC products. The laminate foil can be designed in a range of wood effects to achieve a traditional appearance.

Woodgrain/Wood Stain Effects

Woodgrain or wood stain effects can be applied to either uPVC or aluminium products. They imitate the heritage appearance of natural wood, making the products ideal to retain the authentic appearance of an older property, or add character to a modern home.

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