Steel screen glossary
The terms you will hear when planning steel screens, doors and windows, explained in plain English.
- Glazing bar
- A slim steel bar that divides a screen or window into separate panes of glass.
- Sightline
- The visible width of a frame or glazing bar when you look straight at it. Steel gives narrower sightlines than most other materials.
- Mullion
- A vertical member that divides a screen or window into sections.
- Transom
- A horizontal member that divides a screen or window, often above door height.
- Top light
- A fixed glazed panel above a door, used to fill a tall opening.
- Side light
- A fixed glazed panel beside a door.
- W20 section
- A traditional hot-rolled steel profile widely used for internal steel screens and heritage windows.
- Toughened glass
- Glass heat-treated to be stronger than ordinary glass and to break into small, blunt pieces. Classified under BS EN 12150.
- Laminated glass
- Two or more glass layers bonded with an interlayer that holds the glass together if it breaks. Acoustic versions reduce sound.
- Reeded glass
- Glass with a ribbed, fluted surface that gives privacy while letting light through.
- Pivot door
- A door that rotates on pivots in the floor and head of the frame rather than on side hinges.
- Powder coating
- A durable paint finish applied as a dry powder and baked on. RAL 9005 jet black is the most common colour for steel screens.
- Galvanising
- Coating steel with zinc, usually by hot-dipping, to protect it from corrosion. External steel windows are galvanised before powder coating.
- Thermally improved section
- A steel section designed to reduce heat loss through the frame so steel windows can meet modern energy rules.
- Protected escape route
- A route, such as an enclosed stair, built to resist fire for a set time so people can leave the building safely.
- Integrity and insulation (E and EI)
- Fire-resistance ratings. E means the screen stops flames and hot gases; EI also limits heat on the protected side.
- Article 4 direction
- A council order that removes certain permitted development rights in a conservation area, often including window replacement.
- Crittall-style
- A common description of slim steel windows with glazing bars, after the historic manufacturer. Crittall is a registered trademark of Crittall Windows Ltd.
Quick definitions
What does glazing bar mean?
A slim steel bar that divides a screen or window into separate panes of glass.
What does sightline mean?
The visible width of a frame or glazing bar when you look straight at it. Steel gives narrower sightlines than most other materials.
What does mullion mean?
A vertical member that divides a screen or window into sections.
What does transom mean?
A horizontal member that divides a screen or window, often above door height.
What does top light mean?
A fixed glazed panel above a door, used to fill a tall opening.
What does side light mean?
A fixed glazed panel beside a door.