Types of Sash Window and How to Identify Yours

What makes a window a sash

A sash is simply a framed panel of glass that slides rather than swings. In the classic vertical sliding sash, two sashes sit one in front of the other and move up and down past each other in the same frame. The counterbalance that stops the sashes crashing down is what separates most of the types below, and it is also the thing that most often needs attention on an older window.

Lots of homes also have windows that look like sashes but open on hinges. These are casement windows styled to look traditional, and they are covered in our casement guides rather than here.

Box sash windows with weights and cords

The traditional box sash hides a hollow box in each side of the frame. Inside, cast iron or lead weights hang on cords that run over pulleys near the top of the frame and are fixed to the sides of each sash. The weights balance the sash so it stays wherever you leave it. This is the type found in most Victorian and Edwardian houses.

When a cord snaps, the sash drops or will not stay open. Replacing cords, easing sticking beads and fitting draught seals are all standard restoration jobs, and the timber itself can often be repaired where rot is limited to small areas.

Spiral balance sash windows

Later sash windows, and many replacements, use spiral balances instead of weights. These are sprung tubes fitted in channels at the sides of the sash, so the frame no longer needs deep weight boxes. The sightlines can be a little different from a true box sash because the frame is slimmer at the sides.

Spiral balances can weaken over time, which shows up as a sash that creeps down on its own or feels heavy to lift. Worn balances can usually be replaced without changing the whole window.

Horizontal sliding sashes

A horizontal sliding sash, often called a Yorkshire light, has one or more sashes that slide sideways in the frame rather than up and down. They are more common in cottages and small outbuildings than in town houses, and they have no weights at all, just runners along the bottom.

Modern uPVC and timber sash windows

Modern replacement sashes keep the vertical sliding look but use sealed double glazed units, modern seals and, on uPVC versions, a tilt function so the sashes lean inwards for cleaning. We supply uPVC sash windows with tilt cleaning, and for timber windows we either restore the existing frames or replace them in full.

Details such as a run through horn on the top sash, slim meeting rails and applied glazing bars make a big difference to how convincing a replacement looks on an older house, so they are worth asking about at survey.

Glazing patterns you will hear about

Sash windows are often described by how many panes each sash is divided into. A two over two has two panes in the top sash and two in the bottom. Six over six is the Georgian pattern. One over one, with a single pane in each sash, became common later. The pattern is a style choice on a replacement, but on an older house matching what is already there usually looks best.

How to tell which type you have

You can usually identify your windows in a few minutes. Look closely and try the sashes gently, stopping if anything feels loose.

• Sashes slide up and down and the side frames are deep and boxy: likely a box sash with weights
• You can see cords at the edges of the sash when it is open: weights and pulleys
• Slim side channels containing tubes or covers: spiral balances
• Sashes slide sideways along a bottom runner: horizontal sliding sash
• Sealed units, plastic frames and a tilt catch on the sash: modern uPVC sash
• Hinges on one edge and the window swings open: a casement, not a sash

Why the type matters

The type decides what repairs are possible and what a sensible replacement looks like. A sound box sash may be worth restoring, while a failing spiral balance window may be simpler to replace. Our sash window pages explain costs and the choice between uPVC and timber, and a survey will confirm the condition of the frames before anything is decided.

Common questions

What are the main types of sash window?

Traditional box sashes with weights and cords, spiral balance sashes, horizontal sliding sashes and modern uPVC or timber replacement sashes.

How do I know if my sash windows have weights?

Box sashes have deep side frames that hide the weights, and you can often see the cords at the sides of the sash when it is raised.

Why does my sash window not stay open?

On a box sash a broken cord is the usual cause. On a spiral balance window the balance has usually weakened. Both can normally be repaired.

Can uPVC sash windows tilt for cleaning?

Yes, the uPVC sash windows we supply have tilt cleaning, so the sashes lean inwards and you can clean the outside glass from indoors.

Should I restore or replace timber sash windows?

It depends on the condition of the timber. We offer both restoration and full replacement for timber windows and will tell you honestly which makes sense after a survey.