Most sash window parts lists come from companies selling the parts. This one takes its names and definitions from Historic England, Historic Environment Scotland and the Society for the Protection of Ancient Buildings (SPAB). For the styles and periods, and how to tell a Georgian sash from a Victorian one, see our guide to types of sash windows. Other window topics are in our double glazing guides.
Sash window diagram: the parts of a box sash
A double-hung, six-over-six box sash from outside, with the weights drawn through the side of the case. It is a schematic, not a joinery drawing.
The parts labelled, from the top down:
- Head: the top of the case.
- Pulley: near the top of each pulley stile.
- Sash cord: from the sash, over the pulley, to the weight.
- Sash weight: hangs in the hollow side of the case.
- Pulley stile: the side of the case.
- Outer lining: the outside face of the case.
- Top sash and top rail.
- Glazing bar (astragal).
- Parting bead: separates the two sashes.
- Meeting rails: where the two sashes close together.
- Horn: the sash stile carried below the meeting rail.
- Sash fastener: the catch on the meeting rails.
- Staff bead (baton rod): holds the lower sash in.
- Bottom sash, bottom rail and sash lift.
- Pocket piece: opens onto the weights.
- Cill (sill): the bottom of the case.
The parts of a sash window, with their English and Scots names
Historic Environment Scotland's Guide for Practitioners 3, Conservation of Timber Sash and Case Windows (2002), defines a sash and case window as two glazed frames, the sashes, "fitted into but not fixed to the case", with at least one sash, and usually both, sliding vertically and "counter-balanced by an independent system of weights and pulleys". England and Scotland use different words for several of the same parts, and a joiner on either side of the border will use their own, so both are given here.
| Part | English name | Scots name (HES) | What it is |
|---|---|---|---|
| Outer frame | Cased frame, sash box frame | Case, window case | The built-up frame the sashes slide in; its hollow sides hold the weights |
| Side of the frame | Pulley stile | Pulley stile | The side member of the case, carrying the pulleys |
| Inside and outside facings | Linings | Inner lining, outer lining | Enclose the weights; the outer lining also seals the case against water |
| Divider between the sashes | Parting bead | Parting bead | Thin strip fixed to the case that separates the two sashes |
| Bead holding the lower sash | Staff bead | Baton rod | Timber bead on the inner edge of the frame |
| Bars between the panes | Glazing bar | Astragal | Moulded timbers dividing a sash into small panes |
| Middle rails | Meeting rail | Meeting rail | Top rail of the lower sash and bottom rail of the upper, closing to form a weather-tight joint |
| Sides of a sash | Sash stile | Sash stile | The side member of a sash frame |
| Stile extensions | Horns | Horns | Stiles projecting beyond the rails, allowing a full tenon joint |
| Bottom of the frame | Cill | Cill (sill), stone cill | The lower horizontal member of the case |
| Access hatch to the weights | Sash pocket | Pocket piece, pocket cover | Removable piece low in the pulley stile or behind the shutter |
| Counterweight | Sash weight | Sash weight | Hangs on the cord to balance the sash; lead or cast iron |
| Cord | Sash cord | Sash cord | Tied to the sash and the weight; heavy plate-glass sashes sometimes used chains |
| Catch | Sash fastener | Sash fastener | Fixed on one meeting rail, swung across to engage the other |
| Pull | Sash lift | Sash lift | Metal pull or hook for lifting the sash |
Definitions: Historic Environment Scotland, Guide for Practitioners 3 glossary (2002) and Managing Change: Windows (2018); Historic England, Traditional Windows (HEAG039, 2017); SPAB. Trade names you may also hear: box frame, sash box, sash bar, mid-rail (for meeting rail), weight pocket.
The case is usually hidden in the wall. Historic England records that the 1709 Building Act set frames in London and Westminster at least four inches back from the wall face as a fire precaution, and nine inches from 1774; the look spread through England. In Scotland the frame has always sat in a deep check in the masonry for weather protection, says Historic Environment Scotland.
How does a sash window work?
A sliding sash has to be counterbalanced or it would fall shut. In a box sash, Historic England explains, "each sash has its own pulley and cord". The cord is fixed to the side of the sash, runs up over a pulley near the top of the pulley stile, and drops into the hollow side of the case, where it is tied to a weight. Historic England says the weights were generally cylindrical and made of lead or cast iron, and that cords were cotton in the Georgian period; by the later 19th century some substantial houses used linked chain, strong enough for very large plate-glass sashes. The parting bead between the sashes separates them and keeps each in its own groove.
The balance is deliberately uneven. SPAB's maintenance advice is the only source we found that puts numbers on it: upper sashes should be about 0.5 to 0.9 kg lighter than their weights, and lower sashes 0.5 to 0.9 kg heavier. The effect is that the weights hold the top sash up and the bottom sash stays down. Get it wrong and, in SPAB's words, "sashes will rise and drop by their own accord". Where the original weights are too light, add-on make weights can be fitted.
Historic England says the earliest vertically sliding sashes had a fixed top sash, with the lower one wedged or pegged, and that the counterweighted double-hung sash "appears to have been a British invention"; the earliest surviving example dates from 1701.
When a sash creeps down or will not stay up, look at the balance before anything else: the cords, and whether the weights still match what the sash now weighs. Reglazing changes that weight, and the weights do not change themselves.
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Box sash, spiral balance and Yorkshire slider
Three mechanisms get called a sash, and only the first has the parts in the diagram. The box sash, or sash and case, is the weights-and-pulleys window described above.
The spiral balancereplaces the weights. Historic England records that it was patented in 1930: each balance was a cylinder holding a torsion spring and a spiral rod, housed in grooves in the sides of the sashes, and it could be adjusted "within limits" to suit sashes of different weights. Today's uPVC makers describe a spring tube in the frame, so where it sits depends on the system. With no weights there is no need for a hollow box. Historic Environment Scotland notes that the spiral balance, an American innovation of the inter-war period, "was not popular in Scotland".
The Yorkshire slidermoves sideways. Historic Environment Scotland is plain that "strictly speaking the horizontal sliding window is not sash and case", because the frame is solid and the sash is pushed by hand, not counterbalanced. So it has no cords, pulleys or weights to fail. Historic England adds that these windows were not just restricted to Yorkshire.
For cleaning, many Scottish sashes have Simplex hinges, which Historic Environment Scotland says let the lower sash swing inwards for cleaning. On modern uPVC sashes, makers describe both sashes tilting inwards instead.
Meeting rails and horns: why they exist
The meeting rails are where the two sashes overlap, and they close together to form a weather-tight joint. Historic Environment Scotland traces their shape to the parting bead: once a parting bead gave each sash its own groove, it left a gap between the sashes that let draughts and rain through, so the meeting rails were widened to bridge it. The sash fastener sits on the meeting rails; Historic England says it had evolved into the familiar lever-arm pattern by 1800. SPAB notes that excessive wear lets sashes move too freely and the meeting rails settle out of level.
Hornsare the stiles of the sash carried past the meeting rail. Their job is structural. Historic England says the cheaper, stronger plate glass available from the 1830s reduced the need for glazing bars, and the heavier glass, with no bars to support it, "necessitated the introduction of 'sash horns'" to strengthen the joints at either end of the meeting rail. The sources do not agree on when: a caption in the same Historic England guidance puts horns in the late 19th century. Historic Environment Scotland says mid-19th-century sashes were strengthened "sometimes" with horns, and that in Scotland horns "are not very common" and often do not appear until late in the century, if at all.
That matters when a sash is replaced. Historic Environment Scotland says horns "should only be provided if there is historical evidence for their use", and one council's guidance prefers run-through horns, part of the stile, rather than ones planted on. How horns help date a window is covered in our sash window styles guide.
The parts that wear out, and what a repair involves
Because the sashes are fitted into the case rather than fixed to it, a box sash can be taken apart and put back. Cords wear out, and SPAB advises that if one breaks it is worth replacing all of them, using a durable, low-stretch cord sized for the weights and pulleys. Re-cording means taking the sashes out to reach the weight pockets. Historic England photographs the job in order:
- Open the sash pocket.
- Remove the staff bead to free the lower sash.
- Get at the weights, and adjust them if needed to balance the sash.
- Tie a lead "mouse" and string to the new cord.
- Run the mouse over the pulley into the weight box.
- Knot the weight to the new cord.
The beads are the other wear parts. Historic England describes the staff and parting beads as "usually sacrificial elements", and one draught-proofing system replaces both with beads carrying brush seals, one answer to the rattle and cold air covered in our guide to draughty windows. For rot, Historic England points to the base of the pulley stile, the outer lining and the outside of the cill, the places water sits. Historic Environment Scotland puts external repainting at every 5 years, depending on exposure. What each fault looks like on a Scottish window, and how a joiner repairs it in place, is on our sash window repair in Edinburgh page.
Pulleys carry history. Historic England says a pulley can help date a sash when other details have gone: the earliest, late 17th century, were brass wheels set straight into the pulley stile, and by the early 18th century they sat in their own removable blocks. Historic Environment Scotland's advice is to retain and reuse surviving original ironmongery.
What changes when double glazing goes in
A sealed unit is heavier than the single pane it replaces. Historic England's Advice Note 18 (February 2026) says sash windows "may need heavier weights to balance the increased weight of the glass". Historic Environment Scotland says narrow units need the rebates in the sash or the astragals made deeper, by about 6 mm, and that new cords and sometimes heavier weights are required. A spiral balance can only be adjusted "within limits", in Historic England's words, so it has to suit the new weight too.
The glazing bars are the harder limit. Historic England warned in 2017 that it is often impossible to double glaze multi-paned historic windows, even with slim units, without altering the frames and bars. On a sash without bars it notes that the sashes are often replaced while the box is kept and heavier weights added. The routes, with prices, are compared in our guide to retrofit double glazing, and the thin units made for period rebates are covered under slimline double glazing. On a listed building, Historic England says inserting double glazing will usually require listed building consent; the costs that brings are on our listed building window costs page.
Is there a standard sash window size?
No. Historic Environment Scotland says window proportions "can vary considerably" and that the dimensions of each pane are "not dependent on any fixed formula". Trade sites that publish a standard size contradict each other: one puts a six-over-six window at a width to height ratio of 1:1.6, another says Georgian windows are typically twice as tall as they are wide.
The heritage guidance gives measurements only for glazing bars. Historic England says early bars were often almost 40 mm thick, while by the early 19th century some were only 12 mm wide, though up to 38 mm deep for strength. For a new window, every sash is measured for its own opening; our timber windows guide covers the joinery options, and the sash window cost calculator prices a set.
Getting sash windows repaired or priced
If you want sash windows repaired, reglazed or replaced, tell us what you have and Leads 2 Trade will arrange quotes from installers covering your postcode.
Frequently asked questions
A box sash has two sashes, each made of stiles, a top rail, a bottom rail and a meeting rail, with glazing bars dividing the panes. They slide in a case (the frame), whose sides are the pulley stiles. Inside the hollow sides hang the weights on cords running over pulleys. A parting bead separates the two sashes, a staff bead holds the lower one in, and the case sits on a cill. A pocket piece low on the pulley stile gives access to the weights.
Each sash hangs on its own cords, which run over pulleys in the sides of the case to weights hidden in the hollow box behind. The weights counterbalance the sash so it stays where you leave it. SPAB says the upper sash should be about 0.5 to 0.9 kg lighter than its weights and the lower sash 0.5 to 0.9 kg heavier, so the top one stays up and the bottom one stays down. Modern sashes often use spiral balances instead.
The parting bead is a thin strip fixed in the middle of each pulley stile that separates the two sashes and gives each its own groove. The staff bead is fitted on the inner edge of the frame and holds the lower sash in from the room side. In Scotland the staff bead is called a baton rod. Historic England describes both beads as usually sacrificial, which means they are expected to wear and be replaced.
Horns are extensions of the sash stiles beyond the meeting rail. Historic England says they were introduced to strengthen the joints at either end of the meeting rail once heavier plate glass removed the glazing bars that had supported it. Historic Environment Scotland defines them as a projection that allows a full tenon joint, and says horns are not very common in Scotland and often do not appear until late in the 19th century, if at all.
Heavy enough to balance the sash they carry, which varies by window. SPAB's rule is that upper sashes should be about 0.5 to 0.9 kg lighter than their weights and lower sashes 0.5 to 0.9 kg heavier. If the weights are wrong the sashes rise or drop by themselves. Where more weight is needed, add-on make weights are available.
It is the Scots name for the same window English guides call a box sash. Historic Environment Scotland describes two glazed sashes fitted into, but not fixed to, a case, with at least one sliding vertically on an independent system of weights and pulleys. Its own guidance also uses 'sash case or box', so the two names describe one type.
No. Historic Environment Scotland says window proportions can vary considerably and pane sizes do not follow any fixed formula. Trade sites publish size ranges, but they disagree with each other, so every sash is measured for its own opening.
Usually, yes. A double glazed unit is heavier than the single pane it replaces, so Historic England says sash windows may need heavier weights to balance the glass, and Historic Environment Scotland says new cords and sometimes heavier weights are needed. The rebates that hold the glass may also need cutting about 6 mm deeper.