A conventional cylinder can be ‘bumped’ using a special key with ridges that are all the same length. A thief will insert the bump-key and strike it to knock the pins into the shear line. Anti-bump locks feature more pins and specific internal mechanisms to prevent this method of entry.

Lock picking involves using small tools to turn the barrel of a lock whilst pushing the pins up to mimic a key. Anti-pick cylinders are designed with spool pins or mushroom pins that ‘catch’ when picked, preventing the lock from turning.

Lock snapping occurs when the cylinder overhangs the handle and is snapped off by force. An anti-snap cylinder features ‘sacrificial cut lines’ on the outside. If attacked, the tip snaps off, but the central mechanism remains intact and locked, protecting the integrity of the door.

Astragal bars are fitted to the glazing both internally and externally. Unlike Georgian bars (which are inside the glass), Astragal bars give the authentic look and feel of separate panes of glass, replicating traditional period features found in conservation areas.

Also known as chamfered frames, these have a flat, angular profile. Because of their sleeker, cleaner appearance, they are commonly chosen for new-builds, extensions, and modern homes.

Doors that slide and fold in a concertina style. When open, the bi-fold door panels stack neatly against the wall to create a seamless opening between inside and outside. They maximize the aperture opening compared to sliding doors.

A window hinged at the bottom of the frame that opens inwards from the top. They are often used for ventilation in basements or pantries.

The lower horizontal bar situated across the bottom of the sash. In traditional sliding sash windows, the bottom rail is often deeper (taller) than the other sections of the frame for visual weight.

The UK’s most common window design. A casement window is attached to its frame by one or more hinges at the side. They are available in uPVC, timber, or aluminium and usually open outwards.

Usually found in pitched roof windows. The sash pivots in the middle of the opening; when fully opened, the top half enters the room while the bottom half exits it.

Characterised by straight lines and bevelled edges (rather than curves). This frame style offers a modern, minimalist look with clean lines. The alternative is a “sculptured” or “ovolo” profile.

The lower horizontal member or shelf of a window or door frame. The external cill is angled to throw rainwater clear of the wall below to prevent damp.

Composite means made up of several elements. In glazing, this usually refers to Composite Doors, which combine materials like wood, PVC, insulating foam, and GRP (Glass Reinforced Plastic) to create a door that is stronger and more thermally efficient than a standard single-material door.

Historically referring to the 1995 Act, now largely replaced by the Equality Act 2010. In glazing terms, “DDA Compliant” refers to products designed for accessibility, such as low thresholds for wheelchairs or longer door handles for easier leverage.

Also known as hinge bolts. These are steel pins fitted into the hinge side of a door or window. When closed, the pin slots into the frame, preventing intruders from removing the door by attacking or removing the external hinges.

A sealed unit consisting of two panes of glass separated by a spacer bar. The space between the panes is filled with air or Argon gas to create an insulating barrier that reduces heat loss and noise.

A scale that illustrates the energy efficiency of a door, with E being the lowest and A++ being the most insulating. This helps consumers compare the thermal performance of different door sets.

Specialized window hinges with a wide opening angle (often 90 degrees) to create a clear exit route in the event of a fire. These are required for certain windows to satisfy Approved Document B of the Building Regulations (Fire Safety).

A window that does not open. These are often used in combination with opening casements to allow light into a room where ventilation is not required.

A window where the opening sash sits flush within the frame, rather than overlapping it. This creates a flat, elegant surface that mimics traditional pre-1932 timber windows.

A pair of hinged doors that open outwards or inwards. They usually overlap, meaning one ‘Main’ door must open before the ‘Secondary’ door can be released. They provide a classic, wide opening to a garden or patio.

Windows that rotate 180 degrees, allowing the external glass to be cleaned safely from inside the room. They are popular in high-rise buildings or upper floors.

Measures how much solar heat is transmitted through the glass. A G-value of 1.0 means 100% of solar heat enters; 0.0 means none. South-facing rooms may need a lower G-value to prevent overheating.

Internal bars situated inside the sealed glass unit to give the grid-effect appearance of Georgian windows. Unlike Astragal bars, they do not stick out from the glass surface, making them easier to clean.

GRP (Glass Reinforced Plastic) is the tough outer layer used on Composite Doors. It is highly weather-resistant and prevents the door from warping, peeling, or fading.

The top horizontal bar that forms the top of the window frame.

Decorative glass created by using lead strips to create a grid or pattern. Historically used because large panes of glass could not be manufactured, but now used purely for aesthetic reasons.

Low Emissivity glass. This glass has a microscopic coating that reflects radiant heat back into the room, significantly reducing heat loss and improving the window’s U-value.

In a set of double doors or French doors, this is the primary door that opens first and houses the main locking mechanism. (Historically referred to as the master door).

A vertical bar or structural element that divides two window units or screens.

The inside of a modern uPVC frame is not hollow; it is divided into multiple air chambers. These pockets trap air, acting like layers of clothing, to create a thermal barrier that stops heat from passing through the frame.

A security mechanism that bolts the door or window into the frame at multiple points (top, middle, and bottom) simultaneously with the turn of a key or handle. Common on uPVC doors.

“Ovolo” means “little egg” in Italian. In glazing, it refers to a sculpted, curved profile shape used for frames and beading, offering a softer, more traditional look than chamfered frames.

Approved Document L covers the Conservation of Fuel and Power. It sets the legal standard for energy efficiency (U-values) that all new windows and doors must meet in the UK.

Approved Document Q ensures that windows and doors in new dwellings resist physical attack by a casual or opportunistic burglar.

Steel or aluminium bars inserted inside the hollow chambers of uPVC profiles to add structural strength. This is crucial for large windows, doors, and conservatories.

Usually Toughened or Laminated glass. Toughened glass is heat-treated to be 5x stronger than standard glass and shatters into small, safe cubes rather than sharp shards. Required by law in doors and low-level windows.

The part of the window or door that actually holds the glass and moves (opens/closes). This sits inside the outer frame.

A decorative detail on sliding sash windows. Originally used to strengthen the joints in Victorian timber windows, they are now added to modern uPVC sash windows to maintain authentic period character.

In a set of French doors, this is the door that is bolted into the frame top and bottom and can only be opened after the Main door is opened.

A police initiative that guides and encourages manufacturers to adopt crime prevention measures in the design of windows and doors. SBD products are tested to rigorous security standards.

High-security locking rods that shoot out from the top and bottom corners of the sash into the frame when the handle is turned.

Narrow vertical windows installed directly next to a door frame to fill wide apertures and bring light into a hallway.

A traditional window style where the sashes slide vertically up and down using a system of weights and pulleys (or modern balances), rather than opening on a hinge.

The vertical sections running up the outer edges of a sash or door frame.

Used in Aluminium windows. Because metal conducts cold, a polyamide plastic barrier is placed between the internal and external metal frames to stop heat escaping.

A versatile European window style. Turn the handle once, and the window tilts inwards at the top for ventilation. Turn it further, and it swings inwards like a door for easy cleaning or emergency exit.

Small windows situated above a door or larger window. Commonly found in tall hallways to bring in light without compromising privacy.

A single operating door within a bi-fold door set. It allows you to enter and exit quickly without having to unlock and fold back the entire set of doors.

A horizontal structural beam or bar that separates a door from a window above it (fanlight).

A safety device used on sash windows to stop the window from opening past a certain point (usually 100mm) to prevent falls or intrusion.

Small vents integrated into the top of the window frame. They allow background ventilation to prevent condensation and improve air quality without having to open the window.

Three panes of glass with two gas-filled cavities. Provides superior thermal efficiency and noise reduction compared to double glazing, often achieving U-values as low as 0.8.

The measure of heat loss through a specific material (like glass or frame). The lower the U-value, the better the insulation. For example, a modern window might have a U-value of 1.2 W/m²K, whereas single glazing is around 5.8.

The side-post or vertical lining of a doorway or window aperture. The masonry parts surrounding the window frame are often called the “reveals”.

A bar that separates the panes of glass in double glazing. Unlike old aluminium bars which conducted cold, “warm edge” spacers are made from low-conductivity composites to keep the edge of the glass warm and reduce condensation.

Rubber seals found around the opening sash and the frame. When the window is closed, these gaskets compress to create a watertight and airtight seal, preventing draughts.

A rating system managed by the British Fenestration Rating Council (BFRC). Similar to the rainbow stickers on fridges, it grades windows from E (poor) to A++ (excellent) based on their ability to retain heat, block drafts, and capture solar warmth.