Sliding Door Glossary: Terms Explained

A B C D F G I L M O P R S T U W

Anodised finish: An anodised finish is a hard, protective oxide layer grown electrically on the surface of aluminium. It gives a metallic look in silver, bronze or black tones and is an alternative to powder coating.
Anti-lift block: An anti-lift block is a security stop fitted in the frame or track that prevents a sliding panel being lifted off its rollers from outside. It is a key part of a secure sliding door.
Approved Document K: Approved Document K is the official guidance in England on protection from falling, collision and impact. It treats glazing in doors as a critical location that must use safety glass.
Approved Document L: Approved Document L is the official guidance in England on conserving fuel and power. It sets minimum thermal performance for new and replacement doors and windows. Wales has its own version.
Approved Document Q: Approved Document Q is the official guidance in England on security in new dwellings. It applies to doors and windows in newly built homes, not to replacement doors in existing houses.
Argon fill: Argon fill is an inert, colourless gas sealed into the gap between the panes of a sealed unit. It slows heat transfer better than air, improving the insulation of the glass.
Article 4 direction: An Article 4 direction is a council order that removes some permitted development rights in a defined area, often a conservation area. Changing doors there may need planning permission.
Brush pile: Brush pile is a strip of dense, fine bristles fitted along the edges of a sliding panel. It helps keep out draughts, dust and insects while letting the panel slide smoothly.
Building notice: A building notice is a simple way to tell Building Control you are starting work, without submitting full plans first. An inspector then checks the work on site as it goes ahead.
Building Regulations: Building Regulations are the legal minimum standards for building work, covering safety, energy use, structure and access. In England and Wales replacement doors are controlled fittings, so the work must comply and be certified or notified; Scotland and Northern Ireland have their own building standards and approval routes.
Building warrant: A building warrant is the formal approval needed in Scotland before certain building work starts. Forming or widening an opening needs one, while like-for-like door replacement in a house usually does not.
Competent person scheme: A competent person scheme is a government-authorised register of installers who can self-certify that their work meets the Building Regulations. The installer notifies the work and the homeowner receives a certificate.
Corner post: A corner post is the vertical frame member where two sliding door elevations meet at a corner. On some corner doors the post is removed so the panels open to leave the corner fully clear.
Critical location: A critical location is an area where glass is at high risk of human impact, such as in and around doors. Glazing in a critical location must be toughened or laminated safety glass.
Drainage slot: A drainage slot is a small opening in the bottom of the frame or track that lets rainwater escape outside. Slots must be kept clear of dirt so water cannot build up or leak inside.
Dual colour: Dual colour means the frame is finished in one colour outside and a different colour inside. A common example is anthracite grey outside with white inside to suit the room decoration.
Foil (uPVC): A foil is a thin, coloured or woodgrain film bonded to the surface of a uPVC frame. It lets uPVC doors come in colours other than white, such as grey, black or oak effect.
g-value: A g-value measures how much of the sun's heat passes through glass, on a scale from 0 to 1. A lower g-value keeps rooms cooler in summer; a higher one lets in more winter warmth.
Integral blinds: Integral blinds are blinds sealed inside the cavity of the sealed unit, between the panes of glass. They stay free of dust and are operated by a magnetic slider or motor.
Interlock: An interlock is the vertical section where two sliding panels meet and overlap when the door is closed. It seals the join and usually forms the slimmest sightline on the door.
Laminated glass: Laminated glass is two or more panes bonded together with a tough plastic interlayer. If it breaks, the pieces stay stuck to the interlayer, which improves safety, security and noise reduction.
Lift and slide: Lift and slide is a sliding door system where turning the handle lifts the panel onto its rollers so it can glide, then lowers it to seal. It suits large, heavy panels.
Lintel: A lintel is a horizontal beam over an opening that carries the weight of the wall above. Widening an opening for a sliding door usually needs a new, larger lintel or steel beam.
Listed building consent: Listed building consent is permission from the council to alter a listed building. It is usually needed to change doors or openings on a listed property, alongside any planning permission.
Low-E coating: A low-E coating is a microscopically thin metal oxide layer on glass that reflects heat back into the room. It improves insulation without noticeably changing how clear the glass looks.
Made to measure: Made to measure means the door is manufactured to the exact sizes and specification confirmed at survey. Made-to-measure goods are excluded from the usual 14-day cancellation right.
Multi-track: Multi-track describes a sliding door frame with three or more tracks, so panels can stack behind one another. More of the opening clears when the door is fully open.
Multipoint lock: A multipoint lock is a locking system that secures a door at several points along the frame from one handle or key. It holds the panel more securely than a single lock.
Outer frame: The outer frame is the fixed perimeter of the door that is fitted into the wall opening. It holds the tracks, seals and drainage, and the sashes slide within it.
Padstone: A padstone is a solid block, usually concrete or engineering brick, set under each end of a steel beam or lintel. It spreads the load safely into the wall below.
Party Wall Act: The Party Wall etc. Act 1996 (England and Wales) sets out how work affecting a wall shared with a neighbour is handled. It may apply if new steelwork for a wider opening bears on a party wall.
PAS 24: PAS 24 is the UK enhanced security test standard for doorsets and windows. It tests how well a door resists attempted break-in using common tools. Sliding door systems are available tested to PAS 24.
Permitted development: Permitted development is a set of rights allowing some building work without a planning application. Replacing doors on a house is usually permitted development if the new doors look similar.
Pocket door: A pocket door is a sliding door that disappears into a cavity built inside the wall when open. External pocket doors leave the whole opening clear; internal ones save floor space.
Powder coating: Powder coating is a durable paint finish applied to aluminium as a dry powder, then baked so it melts into a smooth, hard layer. It resists fading, chipping and weather.
PSK: PSK stands for parallel sliding and tilting, a German term used for tilt and slide doors. The panel tilts inwards for ventilation or moves out and slides to open.
RAL colour: A RAL colour is a shade from a standard European colour chart, identified by a four-digit number, such as RAL 7016 anthracite grey. It lets you match frame colours precisely.
Roller: A roller is a small wheel assembly fitted under a sliding panel that lets it run along the track. Worn or damaged rollers make a door heavy, noisy or hard to slide.
Sash: A sash is a single moving or fixed glazed panel within a sliding door frame. A two-panel slider usually has one sliding sash and one fixed sash.
Sealed unit: A sealed unit is two or three panes of glass joined around the edge with a spacer and sealed airtight. It is the insulating glass fitted into each sliding door panel.
Secured by Design: Secured by Design is a police-backed scheme that promotes crime prevention in buildings. Its requirements for doors build on the PAS 24 security test standard.
Sightline: A sightline is the visible width of frame seen when looking through a closed door, especially at the interlock. Slimmer sightlines mean more glass and a clearer view.
Soft close: Soft close is a damper mechanism that catches a sliding panel near the end of its travel and draws it gently shut. It stops the panel slamming and protects fingers.
Steel beam: A steel beam is a structural steel section that carries the load of the wall or floor above a wide opening. Its size is set by structural calculations.
Structural calculations: Structural calculations are an engineer's workings that size the beam, lintel and padstones for a new or wider opening. Building Control needs them to approve the work.
Structural opening: The structural opening is the hole in the wall, measured brick to brick, that the door frame fits into. It is measured precisely at survey before a made-to-measure door is ordered.
Thermal break: A thermal break is an insulating strip, usually polyamide, built into an aluminium frame to separate the inside and outside metal. It reduces heat loss and the risk of condensation.
Threshold: The threshold is the bottom section of the door frame that you step over. Low thresholds are typically 15–25 mm high, and flush thresholds need a drainage channel outside.
Tilt and slide: Tilt and slide is a door that tilts inwards at the top for secure ventilation, or lifts out and slides sideways to open fully. It is also known as PSK.
Toughened glass: Toughened glass is glass heat-treated to be several times stronger than ordinary glass. If it breaks, it shatters into small, blunt pieces rather than sharp shards, making it a safety glass.
Track: The track is the rail at the bottom, and sometimes the top, of a sliding door frame that the panels run along. Keeping it clean helps the door slide smoothly.
U-value: A U-value measures how much heat passes through a building element, in watts per square metre per degree (W/m²K). The lower the U-value, the better the insulation.
Ug value: A Ug value is the U-value of the glass alone, measured at the centre of the pane. It does not include the frame, so it is usually lower than the whole-door figure.
Uw/Ud value: A Uw or Ud value is the U-value of the whole window (Uw) or whole door (Ud), including glass, frame and spacers. It is the figure used for Building Regulations compliance.
Warm edge spacer: A warm edge spacer is a low-conductivity strip that separates the panes around the edge of a sealed unit. It reduces heat loss and condensation at the glass edges compared with aluminium spacers.
Weather seal: A weather seal is a rubber gasket or strip fitted around the sashes and frame that closes the gaps when the door is shut. It keeps out wind, rain and draughts.

Sliding door glossary

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Sliding door glossary

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