What sash window draught proofing includes

What is included as standard

• Both sashes removed and refitted
• All four sash cords replaced
• Weights checked and counterbalancing adjusted
• Pulleys cleaned and lubricated, squeaks removed
• Sashes eased so they run freely and the meeting rails align
• New parting bead with integral carrier and brush pile
• New staff bead with integral carrier and brush pile
• Pile routed into the meeting rails, the top rail and the bottom rail
• Perished putty made good
• Minor defects and minor rot made good
• Painted-shut sashes freed and made to work again
• Final adjustment and operation check

Where the seals actually go

Historic England splits draught-proofing seals into two families. Compression seals work where a moving part closes against something. Wiper seals work where parts slide past each other — and the guidance is unambiguous that wiper seals are the only way of sealing the sides and meeting rails of a sliding sash window. Brush pile is the standard wiper seal because it copes with a gap that varies along its length, which is exactly what an old window has.

That is why a strip stuck to one face rarely works: it addresses one of five leak paths, and usually the easiest one.

Step 1 — Survey, before anything else

A survey typically takes 40–60 minutes. It establishes what condition the timber is in, whether the sashes have dropped, whether the cords and pulleys are serviceable, and whether there is rot at the cill or the base of the stiles. It also settles two safety questions.

The first is structural. Historic England warns that windows firmly stuck in place may have assumed a structural role and be carrying the wall above, usually because a lintel has failed or moved. Those windows are not forced open; the frame is propped and the cause dealt with first.

The second is lead paint. On older buildings the safe assumption is that lead paint is present unless proven otherwise, and precautions are taken accordingly.

Steps 2–5 — Stripping the window down

1. Remove the staff bead. A knife is run round first to break the paint seal, then the bead is eased off. It is usually sacrificial — it will be replaced with a new bead carrying a pile carrier.
2. Take out the lower sash. The cords are untied or cut with the weights held. Sashes and parts are labelled so they return to the correct opening, with photographs and measurements recorded first.
3. Remove the parting bead. Knife round to break the paint, then lever it out of its groove in the pulley stile, including the head. It is almost always replaced rather than reused, because the replacement is what carries the pile.
4. Take out the upper sash, the same way.
5. Open the weight pockets. Cords, weights and pulleys are inspected, all four cords renewed, and seized axle pulleys freed or lubricated. Over-painting and lack of lubrication are two of the standard reasons a sash stops moving.

Steps 6–8 — Easing, repairs and putty

Easing and de-rattling. The sash stiles and rails are planed or adjusted so the sash runs without binding and — the part that matters most — so the meeting rails come back into close alignment when the window is rebuilt. Fitting a seal to misaligned meeting rails does not seal them; it just makes the window stiff.

Repairs. Rot is spliced out of the cill, the bottom rails and the base of the stiles and jambs. Those are the classic failure points, because water sits on cills and creeps into the joint between the timber cill and the masonry sub-cill below. Epoxy resin repairs alongside conventional carpentry are endorsed by Historic England for this work.

Putty. Cracked, loose or missing putty is made good. This is not cosmetic — failed putty is a genuine air and water path, and loose glass rattles independently of the sashes. Paint should then cover the putty and lap onto the glass to seal the joint.

Steps 9–10 — Routing and new beads

This is the stage that separates professional work from a DIY strip. A router with a straight flute cutter — 8mm is the commonly reported size, cut to around 3.5mm depth for a flush fit — is used to cut a clean groove into the meeting rail and the other seal positions. The accuracy of that groove is what gives the carrier a stable seat. The carrier is bonded in, typically with a silicone-based adhesive, and the pile is inserted once it has set.

New parting and staff beads are then fitted. These are bought in as mouldings, normally in 3m lengths, and come in a few forms: heritage timber parting bead with the pile set directly into the timber and no plastic carrier, which looks more authentic; primed timber with a plastic brush carrier from which the pile slides out so the bead can be painted without fouling the seal; and wood-composite versions. Which is appropriate depends on the window and, on a listed building, on what your conservation officer will accept. See parting beads and staff beads for the detail.

Steps 11–13 — Re-hanging and making good

The sashes go back on new cords, with the weights adjusted for the extra friction the pile adds. If the glazing has been changed at the same time the weights must change too — Historic England notes double glazing can add up to four times the weight of single glazing, which throws the balance completely.

Hardware is fitted last. A screw-action Brighton fastener is generally preferred over a fitch catch on a draught-proofed window, because the screw action physically pulls the meeting rails together, which improves both the seal and security. Sash lifts and, where wanted, security restrictors are fitted at the same time — commonly a pair of bolts set around 100mm above the lower rail, so the window can be left open for ventilation without opening far enough to climb through.

Then making good. Bare timber from routing and rebating is primed. If the window needed painting before the work, it will certainly need painting after.

What is normally an extra

• Rot repair beyond "minor" — cill replacement or splice, stile repairs, a new lower rail, a replacement sash.
• Security restrictors and sash stops — included by some firms, around £40 a set at others.
• Replacement furniture — fastener and sash lifts, around £40 a set.
• Decoration — internal and external, usually priced separately.
• Glazing work — re-glazing, cracked panes, or rebating the sash to take a slim double-glazed unit. This forces re-counterbalancing.
• Secondary glazing — a different product entirely; see the comparison.

Figures for all of these are on the cost page.

Guarantees and how long it lasts

Guarantees in this trade run to around five years on the pile, with roughly ten years of service expected in practice; some firms offer ten years on the whole system. When the pile does eventually flatten it slides out of its carrier and is replaced without touching the timber, which is the main practical advantage of a carrier system over anything glued on.

The commonest cause of premature failure is not wear. It is a decorator painting over the pile.

How long it takes

Reported rates vary with scope: roughly three to five windows a day for draught proofing alone, down to one window a day where a full renovation with repairs is involved. Work is done from inside, room by room, so a house is not opened up all at once. Expect dust sheets, some noise from the router, and each room's windows to be out of action for the working day.

If you want a price for your own windows, send us the number of sashes and your postcode from the contact page, or read what it costs first.

Last reviewed: 28 July 2026.