The mechanics of a vertical sliding sash, and how today's versions handle draughts, cleaning and security.
Short answer: a sliding sash window has two glazed panels, called sashes, that slide up and down past each other in a frame. Traditional versions ran on weights and cords hidden in a box; modern uPVC and timber-effect versions use balances in the frame, add seals that stop draughts, and let both sashes tilt inwards so you can clean the outside from indoors.
They are a defining feature of Georgian, Victorian and Edwardian houses, which is why matching the look matters as much as the performance.
In an original box sash, cords run over pulleys to cast-iron weights inside the frame, so each sash stays where you leave it. Over time cords snap, timber swells and gaps open up, which is where the familiar rattles and draughts come from.
Modern sashes replace the weights with balances concealed in the frame. The sash still slides vertically and stays in position, but there is nothing to rot or break in the same way.
Compared with an original timber sash, a replacement typically brings:
The details that make a sash convincing are slim sightlines, run-through horns on the top sash and proportions that match the original openings. Woodgrain foils give a realistic timber appearance, and heritage profiles with mechanical joints are designed with conservation areas in mind.
Heritage-style sashes are suitable for many conservation areas, but rules vary between councils, and listed buildings normally need consent for any window change. It is worth checking before ordering, especially on a front elevation.
If the original timber is sound and the house is listed, repair and draught-proofing may be the right route. Where frames are rotten, heavily painted shut or losing heat badly, replacement is usually more practical over the long term.
Small details decide whether a replacement sash looks right from the street. Run-through horns, the little extensions at the bottom of the top sash stiles, are expected on many Victorian houses. Georgian bars divide the glass into smaller panes and can be fitted to match the originals, and the width of the meeting rail where the two sashes overlap should be kept slim.
Colour matters too. White remains the classic choice, while woodgrain finishes and heritage shades suit houses where painted timber was traditional. Photographing your existing windows before the survey helps the installer match proportions accurately.
We will match your existing proportions and send a fixed quote. We beat any like-for-like quote.
Traditional sashes use hidden weights on cords; modern ones use balances in the frame. Either way the sash stays where you leave it.
Our modern sash windows have sashes that tilt inwards, so both sides of the glass can be cleaned from inside the room.
Heritage-style designs are accepted in many conservation areas, but it depends on the council. Listed buildings normally need consent for any change.
Worn cords, shrunken timber and gaps between the sash and frame. Modern sashes add seals that deal with this.