Jargon-busting: Glossary of sash windows

Sash window by Premier Windows in London. White windows on cladding with Georgian bars.Sash windows add character to a home and the classic design suits both new and older property styles alike.

We’ve compiled a list of common sash window terms and their meanings to help you when considering purchasing new timber or uPVC sash windows.

Weights and pulleys

Most traditional sash windows operate using a weights and pulley system. Here the counter weight (usually steel, lead or cast iron) is connected to the window by a sash cord which runs over a pulley to open and close the window. Modern sash windows might use spiral balances made up of steel spiral rod and tension springs instead of weights and pulleys, providing a smoother operation.

Weight pocket

Also known as a ‘box’, hence the phrase ‘box sash window’. The weight pocket is where the weights hang vertically inside the frame or wall, which move up and down for the window to open and close. Windows which use spiral balances don’t require a weight pocket, giving you a larger window opening.

Bottom rail

The bottom rail is the horizontal piece framing the window under the sash. Some uPVC sash window manufacturers make windows with a deep bottom rail, to replicate the original features of a traditional timber window.

Astragal bar

Also referred to as a glazing bar, muntin or Georgian bar, this is the strip of wood or uPVC which separates the panes of glass in a window. Original single glazed sash windows were made up of lots of small squares of glass, giving a rippled light effect when viewing the window from afar. Nowadays, you can get stick-on astragal bars that give the traditional Georgian sash appearance.

Sash horn

A sash horn is the pointed detailing on the bottom corners of the top sash. It was originally designed to strengthen the joints and prevent the windows from being opened too far. Although uPVC sash windows don’t need this detail, many will have it to replicate the look of a traditional timber sash window. Most horns are bolt on, but some manufacturers use a run-through horn for a more authentic appearance.

Staff bead

Beading a pane involves using either a timber or plastic strip to hold the bottom sash in place. It’s nailed or screwed to the lining and can be weatherproofed with a draught strip to stop heat loss and improve thermal performance.


The window cill is the base on which the sash window sits, fitted internally at the base of the sashes. Cills are built with a slight incline so that water drains away from the window to the outside, reducing the risk of problems in timber sash windows such as swelling and rotting.

Trickle vent

A trickle vent is a small closable opening in the top sash of the window. It provides a small flow of air to provide ventilation to the living space, reducing the risk of damp, mould and preventing frame rot for timber windows. Modern sash windows will all feature trickle vents.

Premier Windows installs uPVC and timber sash windows, so whether you’re replacing like for like or want to upgrade your old windows, we have a style for you. Call us today on 020 8683 4446 or click here to fill out our easy form and get a quote.