Book Virtual Appointment


The A to Z of words, terms and phrases used within the fenestration industry.


Acoustic windows

These windows are made with acoustic glass that reduces noise pollution. Especially good for reducing noise from airports and busy roads.


Independent testing and quality standards from external bodies to verify products, services and processes. See Sidey’’s full range of accreditations.


High levels of airtightness are required for highly energy-efficient properties – also see Passivhaus.


An anti-lift feature stops external sliding doors from being lifted to gain unlawful entry.


To prevent burglars snapping a cylinder lock, choose an anti-snap feature for your entrance door.

Astragal bars

Also known as Georgian bars, there are various options available from strips applied to the external glass of windows and doors to give the appearance of smaller individual panes.

‘A’ Rated Energy Windows

Window Energy Ratings show the energy performance of windows in an easy colour coded label, as you will find on electrical appliances, such as refrigerators and washing machines.  



Another name for soffit.

Bay Window

A window projecting outward from the main walls of a building and forming a bay in a room.


The British Board of Agrement is one of the UK’s construction certification body. BBA Agrement Certificates are recognised by specifiers and other industry decision-makers as proof that products covered by them have been rigorously tested will comply with Building Regulations and will last for a defined period.


Beads clip into the window profile to hold the units in place.

Bevelled glass

Bevelled glass includes a chamfered edge for additional style, especially useful in traditional properties.


The British Fenestration Rating Council (BFRC) is the UK authority for independently verified ratings of energy-efficient windows and doors.

Bi-folding Door

A concertina-style door made up of between 3 and 7 leaves that fold away to create an edge-to-edge opening.


The British Plastics Federation is the leading trade association of the UK plastics industry, representing 80 percent of industry turnover.


British Standards Institute is a multinational business services provider for the production of standards and supply of standards-related services. They were the world’s first national standards body and remain a leading global standards maker. BSI certification is recognised by specifiers and other industry decision-makers as proof products covered by them have been rigorously tested, complying with Building Regulations.

Building Regulations

Building Regulations are Government codes that set out the criteria that new buildings and refurbishment work must conform to. The parts that apply to windows and doors include Part M, Part L and Part F. They help ensure buildings are safe, secure and energy-efficient.

Butt Hinge

A hinge that allows the full closing of a window or door. Butt hinges stand proud of the door or window surface.


Casement Window

The term casement refers to windows that are top, or side hung and open inwards or outwards. Casement windows are available in a wide range of styles.

CE marking

The CE Mark is a declaration from the manufacturer that the window or doors meet the standards and requirements of the relevant European directives.


This style of window frame has a bevelled edge with a flat appearance, rather than a curved finish.


Also referred to as a sill, window cills help to protect the brickwork beneath windows from direct rainfall, while also providing an attractive finish.

Clip on cills

This innovative product makes installing cills onsite very easy as they simply clip into place. They can also be used with the revolutionary Kitfix system for factory fitted windows.


The process of extruding a PVCu profile and gasket simultaneously. 

Composite door

Doors are designed to provide the strength and appearance of timber doors while utilising the thermal benefits and low maintenance of uPVC/GRP, composite doors are manufactured from a combination of materials.


Condensation is a naturally occurring phenomenon. Moisture condenses out of the air onto a cold surface that is said to be below the ‘dew point’. The dew point varies with the air temperature and the amount of moisture it contains. In Spring and Autumn, in particular, the glass temperature can fall to a low level during the night and the dew point can be comparatively high in these seasons. The glass is more often likely to be below the dew point in these conditions and the moisture condenses onto the surface.


Q. What is Condensation?

A. The definition, in short, is “a vapour or gas (air) converting to a liquid”.

Q. How does it happen?

A. It commonly occurs when warm air hits a cold surface (i.e. the window or any metal parts). As an example, you will see this when you take a cold drink out of the fridge on a warm day/room.

Q. Can I stop it?

A. Modern-day sealed units will reduce condensation, and with specific ventilation and insulation, it can be reduced further. The amount of humidity within the property can also affect the amount of condensation you experience.

Q. Do the ‘Seasons’ affect condensation?

A. Yes. In warmer conditions, it can be virtually non-existent. In colder periods you may notice increased amounts of condensation.

Q. What can I do with the condensation?

A. Where possible it is advisable to mop up the excessive moisture.

Q. Why do I see Condensation on the outside of my windows?

A. The improved performance of modern sealed units results in the heat being retained within the building more efficiently therefore the external pane is cooler. When the temperature during the night falls and in the warmer seasons warms up, condensation is noticeable on the outside. In brief, this is nothing to worry about, it is a good sign that the sealed unit is working efficiently.


Curtain walling

Comprising of at least 50% transparent material within walls and 75% of the roof area, a conservatory is a garden room or sunroom attached to a dwelling.

Glazed and panelled walling is used in large buildings, often several storeys high.


Dead Bolt

A secure locking system for modern doors.

Double Glazing

Offering much greater thermal efficiency than traditional single glazed windows, double glazing consists of a unit manufactured from two panes of glass. These panes are separated by a space that is filled with gas or air to reduce heat transfer from inside a property to the outside.

Dummy Sash

Purely for aesthetic purposes, this is a sash that does not open but enhances the appearance or symmetry of a window.

Drip Bar

Help deflect rainwater from residential and composite doors, preventing water pooling.


Energy Efficiency

Keeping a property at a comfortable level of heating while using less energy.


Most of the profiles used in PVCu windows, doors, conservatories and roofline are extruded. Extrusion is the process of pushing PVCu pellets through a die to form a shape.


Fabric First

Focusing on the fabric of the building to increase energy performance.


The fascia is a component of roofline. It is a flat board that sits parallel to the house and the gutter brackets are fixed to it. The fascia, combined with soffits, maintains the integrity of the rafters.

Flush Sash

Ideal for modern properties and homes in conservation areas, this term describes windows where the sash sits flush within the frame, mimicking the style of pre-1932 traditional timber windows.

French Doors

A pair of double opening doors that meet in the middle without a mullion to give a clear, unobstructed opening. They usually comprise glass panes extending for most of their length.

French Window

The same as French doors but used for windows, these are ideal for use as a fire escape.



The black weather-tight seal around your windows and doors.

Georgian Bar

Also called astragal bars, they offer the illusion of small, individual panes of glass within a larger pane. Can be foiled to match your window.

Glazing Bead

The bead clips securely in place around the glazing unit of a window to hold the glass in position and provide a weather-tight seal.


Glass Reinforced Plastic, also known as fibreglass, is a composite material made of plasti



Refers to the handles, hinges and other window and door furniture.

Head drip

Head drips appear at the top of a window and is a means to channelling water away from the front face of the window or door.

Hook lock

A type of door lock that throws a hook or multiple hooks into a keep when the door is locked.

c reinforced with fine fibres of glass. It is an extremely tough material used in the marine industry for its hardwearing and weatherproof characteristics. It is used as the outer skin on composite doors.


Inline Patio Door

A sliding patio door system where the moving door pane slides in front of the fixed pane.

Injection moulding

The manufacturing technique is 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.


The International Organisation of Standardisation (ISO) is an international standard-setting body composed of representatives from various national standards organisations. ISO sets standards for manufacturing and environmental processes.



Designed to accept the locking mechanism of the product, these metal locking points are found on doors and windows.


The original and innovative solution for fenestration products enables offsite building manufacturers to install fully glazed, fully finished windows and doors into their panels as part of the production cycle with little effect on stacking, storage and transportation of the finished panels.


LAPFAG Approval

The Local Authority PVCu Frame Advisory Group (LAPFAG) is made up of many Local Authorities, Housing Associations and other public bodies engaged in the production and specification of PVCu windows. LAPFAG approval helps satisfy Building Regulation requirements.

Large Frame

Remaining static and housing the opening sashes, this is the part of the window or door that is attached to the building. Also, known as the Outer frame.

Low ‘e’ glass

Low emissivity glass varies from normal clear glass in that one side has a special metal coating. Low ‘e’ glass is an insulating glass that blocks heat loss from the home while allowing in the energy from the sun.

Low threshold

Offering easy wheelchair and pushchair access to a property, low thresholds are a family-friendly option that is also available in thermally broken options for greater thermal efficiency.


Main Frame

This is the outer frame that houses the window or door.


This is the silicone seal between the wall and the outer frame. Is also used to seal screw holes and any other element exposed to dampness or moisture.


The vertical section divides window units and provides structural support to the frame.


Outer frame

Housing the opening sashes and remaining static is the part of the window or door that is attached to the building. Also known as the large or mainframe.


This is another term for the sculptured style of window profile.



Equal to one Newton per square metre, this unit is used to measure pressure.

Part B

Setting out guidelines for fire safety, Part B refers to Approved Document B for Building Regulations.

Part L

Setting out thermal efficiency standards that all windows must comply with, Part L refers to Approved Document L for Building Regulations.

Part F

Setting out ventilation guidelines and standards, Part F refers to Approved Document F for Building Regulations.

Part M

Containing the guidelines set out for access to buildings, Part M refers to Approved Document M for Building Regulations.

PAS 24

An independent accreditation guaranteeing that a product is covered by a UKAS accredited certification and a requirement for obtaining Secured by Design (SBD).


Passivhaus, or Passivehouse, refers to a low-energy building that requires little or no energy for space heating or cooling, resulting in a drastically reduced ecological footprint. It uses the principles of fabric first.

Patio Door

Often used to provide access to gardens, this is a set of doors with one or more glazed full sliding panels.


Un-plasticised polyvinyl chloride more usually called PVC or uPVC in Europe and the UK, or vinyl in the USA.


RAL Numbers

The number references colours using the European standardised colour matching system, often used on aluminium windows and doors.


Sometimes steel is required to reinforce PVCu windows, depending on size and application.

Roof Glass

Conservatory and orangery glass roofs can include solar controlled glass to maintain ambient temperatures whatever the season.



The framed part of the window opens and holds the glass in place.

Scratchguard ™

A glass protection system is applied after manufacture to eliminate scratches, abrasions and other construction site damage.


Often used to provide a more traditional appearance, this style of window profile offers a curved edge, rather than bevelled or chamfered.

Secured by Design

This accreditation certifies that the product has been assessed and tested to meet the security standards of the Association of Chief Police Officers.

Self-cleaning glass

Glass uses a dual-action process in which organic dirt is broken down by daylight and is then washed away by the rain, making it easier to keep clean.


Used to securely fasten and lock a door, this is a moveable bar or rod that slides into a socket.

Sidey Recycling Scheme

Do you want money back for your old windows and doors? The new Sidey Recycling Scheme allows you to get between £100-£200 for each of your old windows when you buy new energy efficient windows from us.


See the alternative entry for cill.


An integral within the roofline system, soffit sits on the lip of the fascia and spans back to the wall of the house. It’s designed to keep the inside of the roof free from birds and vermin.


Sidey standard products with U-Values down to 1.2 W/m2K.


Sidey higher specification products with U-Values down to 0.7 W/m2K and innovative products designed for specific requirements. 

Spacer Bars

Spacer bars are used to separate the panes of glass in double glazed, dual glazed or triple glazed units and can be made from stainless steel, aluminium or warm edge.

Structural Couplings

These are used to connect one window or door to another to increase strength, helping with installations in large apertures or with high wind loading.


Thermal Efficiency

Keeping a property at a comfortable level of heating while using less energy.

Tilt & Turn Window

This style of window can be used in two different ways – tilt to allow fresh air inside without comprising security and turn so that they can be easily cleaned from the inside.


A traditional timber joint with all the strength of a PVCu weld.


A horizontal crossbar that divides window panes and provides additional strength.

Triple glazing

Offering even greater thermal efficiency than double glazed panels, triple glazing consists of a unit manufactured from three panes of glass. Each pane is separated by space that is filled with gas or air to reduce heat transfer from inside a property to the outside.

Trickle Vent

Located at the top of the window frame, this is an optional built-in feature that allows ventilation.


Twin Cam Security Locking System is one of the most revolutionary and secure systems on the market with up to eight locking points with adjustable twin-cams offering even greater security against burglary.



Unplasticised polyvinyl chloride, more usually called uPVC or PVCu in Europe and the UK, and vinyl in the USA.


Expressed as W/m2K, this is a measure of heat loss and the lower the U-value, the more thermally efficient the product is.

Domestic U-Values

Non-Domestic U-Values


Vertical Slider

A window in the style of a traditional sliding sash window. PVCu sliding sash windows allow both the top and bottom frames to slide freely. The frames also tilt inwards for easy cleaning.


Warm Edge Spacer Bar

Warm edge spacer bar is a thermally optimised spacer bar made from a highly insulating composite plastic that is thermally resistant up to constant temperatures of 100 degrees C.


Window Energy Ratings – offering a clear way to show consumers the energy rating of a particular product. The familiar coloured ‘rainbow’ label is similar to those you will see on refrigerators and other electrical appliances, with A+ the most energy-efficient.