Parting bead and staff bead: the two components that seal a sash window

What each bead is and does

The parting bead

A box sash frame is built up from linings, and the vertical inner lining the sashes run against is the pulley stile — so called because the axle pulley is set directly into it. Cut into the face of that pulley stile is a shallow groove, and the parting bead sits in it, projecting into the opening far enough to form two separate channels: the outer one for the upper sash, the inner one for the lower. Without it, the two sashes would foul each other.

It is held by friction in that groove, not by pins or glue, precisely because it has to come out whenever the upper sash is removed for re-cording. It runs the full height of the box and continues across the head. Being thin, unpinned and permanently rubbed by two sliding sashes, it is the component most likely to be worn, shrunken or missing altogether — Historic England's schedule of sash window defects lists worn or damaged beads as a standard cause of rattles and draughts.

The staff bead

The staff bead — the stop bead, in some regions — is the innermost bead on the room side, and its job is to retain the lower sash. It is usually a larger, moulded section than the parting bead, mitred at the corners and pinned to the inner lining. It is the first component to come off in any sash job: knife round it, ease it away, and the lower sash is free.

Because it is pinned rather than housed, and because it sits on the room side where it is repainted with every redecoration, the staff bead fails differently: not worn thin, but built up with so many coats that it grips the sash and stops it moving. Historic England lists stop beads fitted too tightly among the standard causes of a sash that will not slide.

How to identify and measure them

Stand inside the room and look at the window. The bead nearest you, the one you could touch without opening anything, is the staff bead. Slide the lower sash up and look into the gap behind it: the thin bead running vertically between the two sashes is the parting bead. If you cannot see one, it has either been painted flush into the stile or is missing — both common, and both reasons the window whistles. Then measure two things: the section of the bead, and the gap it has to seal.

1. Section. Take a small offcut, or measure the exposed bead with a rule or vernier. Parting beads are quoted as thickness × width; staff beads the same. Record both dimensions before you order.
2. Groove depth. For the parting bead, the groove in the pulley stile takes part of the thickness. A bead too thick for the groove will not seat; too thin and it will rock.
3. Running clearance. Work a feeler gauge into the gap between the sash stile and the bead at the top, middle and bottom of the run. This is what sizes the pile, and it is rarely the same at all three points.
4. Length. Measure each run — up one side, across the head, down the other. A 3m length covers one full side on most domestic sashes, so budget two or three lengths of each bead per window.

Standard UK sections are limited, which makes ordering straightforward. Trade suppliers stock timber parting beads at 7 × 25mm, 8 × 25mm, 8 × 28mm and 22 × 14mm, and staff beads at 20 × 15mm, 20 × 20mm, 20 × 24mm, 25 × 15mm and 28 × 15mm. Timber staff and parting beads are generally supplied in 3m lengths, in primed or unprimed finish, with a stated tolerance of −0.20/+0.10mm on width and thickness and ±3mm on length.

A Scottish sash-and-case window uses its own sections — a major supplier list a dedicated Scottish staff bead — so do not assume an English section will drop in north of the border.

The bead options, compared

Once you have decided to replace the beads, there are four routes. All prices below are a major supplier trade prices ex VAT for a single 3m length, checked on 28 July 2026; buying in quantity brings them down substantially.

Heritage timber, pile straight into the moulding

The brushpile is set directly into a slot machined in the timber, with no plastic carrier visible at all. One major supplier's Heritage timber parting bead comes with a 5.5mm white brushpile fitted as standard and was £6.29 for the common 7 × 25mm and 8 × 25mm primed sections, or £6.41 for 8 × 28mm; the matching Heritage staff bead ran £6.29 to £8.98 by section. This is the most authentic-looking option and the one to specify where the beads are visible and the building matters. The trade-off is that the pile is not user-renewable — there is no carrier to slide it out of.

Primed timber with a plastic brush carrier

The same timber bead, but with a pile carrier let into it and the brushpile slotted into the carrier. The pile slides out, so the bead can be primed, undercoated and glossed with the pile removed and put back afterwards. A timber parting bead with carrier and brushpile was £7.09 for 7 × 25mm and £7.35 for 8 × 25mm; the staff bead equivalent was £7.35 for 20 × 15mm, £7.66 for 20 × 20mm and £8.19 for 25 × 15mm. This is the workhorse specification for most draught-proofing work, and the renewability is a real advantage over the life of the window.

Wood-plastic composite

A PVC and wood-fibre blend, sold by a major supplier under the wood-plastic composite name and listed as wood-plastic composite. It machines and pins like timber but does not absorb water, so it will not swell and seize in wet weather. Composite parting beads were £3.99 and staff beads £4.94–£5.57 — the cheapest of the four. Sensible on an exposed elevation or a rental property; less so where the joinery is under conservation scrutiny.

All-plastic beads

Extruded PVC, usually two-part so the outer face clips off. One major supplier's two-part plastic two-part parting bead was £9.17, the single-sided PB4 £5.69 and the two-part PB2 £7.43 in a 2.4m length. These size by total gap rather than running clearance — the two-part plastic is specified as a 5.5mm brush for a 10–11mm gap, 8.5mm for 12–13mm and 11.5mm for 13.5–16mm. Quick and durable, but they look like plastic, and on a period window that is usually the end of the argument.

Why both beads are replaced rather than reused

Homeowners often ask why a draught-proofing quote includes new timber when the old beads look serviceable. There are four reasons, and they compound.

• There is nowhere to put the seal. A wiper seal has to sit flush in the sliding face. On an original bead that means machining a groove into a 7mm-thick moulding already in the window, which is neither practical nor kind to the timber. A new bead arrives with the groove and carrier in it.
• The old beads are worn. Two sashes have been sliding against the parting bead for a century or more. It is thinner than it was and often bowed, so a seal fitted to it is sealing a gap that is already the wrong shape.
• They rarely survive removal. A parting bead painted into its groove for decades usually splits on the way out, particularly across the head. Reuse is a hope, not a plan.
• Paint build-up. Staff beads carry every coat the room has ever had. Stripping one back to a clean, consistent section takes longer than fitting a new one.

In practice, a standard overhaul-and-draught-proof specification from most UK specialists includes new parting beads and new staff beads as a matter of course, alongside four new sash cords and pile routed into the meeting rails. Ours is set out under what the service includes and priced under what it costs.

Taking the old beads out

The sequence is fixed, because each component releases the next. Work in this order, and label the sashes and beads as you go so everything returns to the opening it came from.

1. Knife round the staff bead. Run a sharp trimming knife down the joint between the bead and the inner lining, and along the joint between the bead and the sash, on both faces. The aim is to cut the paint film so it tears at the knife line instead of dragging a strip of finish off the lining. Skipping this is the commonest cause of damage.
2. Ease the staff bead off. Work a broad chisel or a thin flat bar behind it, starting near the middle of a run rather than at a mitre, and lift progressively along the length. Pull the old pins through from the back rather than punching them out through the face.
3. Take out the lower sash. Swing it into the room, cut or untie the cords, and hold each weight so it lowers rather than drops down the weight pocket. Knot the cord ends so they cannot disappear over the axle pulley.
4. Knife round the parting bead. Same principle: cut the paint seal on both sides, full height, before applying any force.
5. Lever the parting bead out of its groove. Grip it with pincers at one end and draw it out, or work a chisel into the groove and prise along the length. Take the head section as well — it is easy to forget and usually the tightest.
6. Take out the upper sash, as for the lower one.

Two safety points before any of this. Historic England warns that a window firmly stuck in place may have taken on a structural role, carrying the wall above through a failed or moved lintel, and that such windows should not be forced — parts of walls have been known to collapse. And on older buildings, assume lead paint is present unless it has been proved otherwise, and take precautions before knifing or sanding anything.

Fitting and pinning the new beads

Fit the parting bead first, because the upper sash has to be back in its channel before the staff bead can go on.

• Clean the groove. Scrape out old paint, glue and grit until the bead seats down to its full depth. A bead riding on debris will sit proud and bind the sash.
• Cut the head length first, then the two verticals up to it. Square butt joints are normal on a parting bead; the staff bead is usually mitred at the corners.
• Do not glue the parting bead. It is a friction fit by design, so that the upper sash can be released again for re-cording. If it is slack, a couple of panel pins driven at an angle into the groove will hold it without committing it.
• Pin the staff bead through the face with lost-head pins into the inner lining, punch below the surface, and fill. Space the pins evenly and keep them clear of the mitres.
• Check the sash runs before you finish. Slide it the full travel. If it drags, the pile is too tall for the gap, the bead is proud in its groove, or the sash needs easing — diagnose it now rather than after the filler has gone in.
• Re-balance if you have added drag. New pile adds friction, so a sash that previously stayed put may now creep. Weight adjustment is part of a proper job.

The meeting rails also need sealing, because the rails slide past each other, and that is a routed groove rather than a bead. UK specialists typically use a router with an 8mm straight flute cutter, bond a pile carrier into the groove with a silicone-based adhesive, and insert the pile once it has cured. One major supplier supplys a TCT cutter for their T-shaped carrier at £27.30 ex VAT, for a router with a ½in collet. If sashes still rattle once the beads are done, the meeting rails are almost always the reason — see rattling sash windows.

Never paint the pile or the carrier

This is the rule broken most often, usually by a decorator who arrives months after the joiner and has no idea what the white plastic strip is for. Gloss soaks into the filaments, sets hard, and the pile stops wiping. The window rattles and draughts again, and it looks as though the draught proofing has failed when in fact it has been painted solid. One London specialist report repeated callbacks from exactly this cause and is blunt that cleaning set gloss out of pile is a waste of time.

How to avoid it. Where the bead has a carrier, pull the retaining pin and slide the pile out before decorating, paint the bead, then slide the pile back once the paint is hard. Where the pile is bedded straight into a Heritage timber bead, mask it. Tell the decorator explicitly — the seals are not obvious to someone who has not fitted them.

If it has already happened. Provided there is a carrier, the fix is cheap: pull the single retaining pin, grip the pile at one end with pliers, slide it out and feed in a fresh length. A 25m coil of 5.5mm brush pile was £8.93 ex VAT from a major supplier in July 2026, enough to redo several windows. With no carrier, the bead itself has to come off and be replaced — the practical argument for specifying a carrier even though the heritage bead looks better.

If your windows are otherwise sound and you are weighing up doing this yourself, our DIY draught proofing guide covers the tools and the point at which the job stops being worth the afternoon, and why sash windows are draughty explains what the beads are actually fighting.

Last reviewed: 28 July 2026.