Published 20 September 2026 · Sash Window Draught Proofing
A broken sash cord is the most common reason an original London sash window stops working. The window becomes heavy, slams shut, or refuses to stay open at all. It is also one of the most straightforward repairs a specialist can carry out, and it does not require replacing the window.
This guide explains what sash cords do, how to tell when they are failing, what replacement costs in London in 2026, and what a correct repair involves.
What sash cords actually do
A traditional box sash window is a balance system. Each sash is connected by cords running over pulleys to cast iron or lead weights hidden inside the box frame. When the weights match the sash, the window glides and stays wherever you leave it.
Cotton cords perish with age, damp and repeated painting. Once one cord breaks, the remaining cords take uneven load and usually fail within months.
Warning signs your cords are failing
- The sash slams down or will not stay open
- One side of the sash rises higher than the other
- A dull knocking sound from inside the frame when the window moves
- Frayed, stiff or paint-clogged cord visible at the pulley
- The window feels suddenly much heavier than before
- A cord end hanging loose in the reveal
A window that will not stay open is a genuine safety risk, particularly above ground floor level and in homes with children. Our article on emergency sash cord replacement warning signs covers the safety issues in detail.
Sash cord replacement cost in London
| Work | Typical cost |
|---|---|
| Single sash re-corded (two cords) | £110 – £180 |
| Full window re-corded (both sashes, four cords) | £160 – £280 |
| Re-cord plus draught proofing in one visit | £280 – £450 |
| Additional windows in the same visit | £120 – £220 each |
| Pulley wheel replacement | £20 – £45 per pulley |
Prices vary with window size, access and the weight of the sashes. Because the sashes must come out for both jobs, combining re-cording with draught proofing is significantly cheaper than booking them separately.
Why both sides should be replaced together
Replacing only the broken cord is a false economy. The surviving cord is the same age, has the same wear, and is already carrying uneven load. Any competent specialist will renew all cords on the window at the same time and re-balance the weights while the sashes are out.
The repair process
- Protect the room and carefully remove the staff bead without splitting it.
- Take out the lower sash, then the parting bead and the upper sash.
- Open the weight pockets in the box frame and withdraw the weights.
- Inspect the pulleys, clearing paint and replacing any seized wheels.
- Weigh the sash and confirm the weights match, adding or exchanging weights where a previous repair left them wrong.
- Fit new waxed braided cords, correctly knotted and pinned into the sash groove.
- Rehang and test both sashes for smooth travel and even closing.
- Refit beads — ideally new staff and parting bead with brush seals fitted at the same time.
Modern waxed polyester-cored braided cord is the usual choice: it looks traditional, resists damp and lasts far longer than plain cotton.
Combine the repair with draught proofing
Once the sashes are out, the labour for sash window draught proofing is largely already done. Fitting new beads with integral brush seals at the same visit removes rattling, stops uncontrolled airflow and cuts window-related heat loss by up to 30%. For noise-affected roads, secondary glazing can be added later without altering the restored window.
Frequently asked questions
How much does sash cord replacement cost in London?
Re-cording a full sash window with both sashes typically costs £160 to £280 in London in 2026. Combined with draught proofing in the same visit, expect £280 to £450 per window.
How long does it take to replace sash cords?
A single window usually takes one to two hours. A specialist working through several windows in a property will normally complete a whole house in one day.
Can I replace a sash cord myself?
It is possible, but the sashes, beads and cast iron weights are heavy and easy to damage, and the glass in period windows is often irreplaceable. On listed or Conservation Area properties, we recommend a specialist.
Should I replace all the cords or just the broken one?
Replace all of them. The remaining cords are the same age and will usually fail soon after, and the sashes have to come out again for each repair.
Do sash cords need replacing on a listed building consent application?
No. Like-for-like cord renewal is routine maintenance and does not normally require listed building consent, as nothing about the window's appearance changes.
How long do new sash cords last?
Good quality waxed braided cord, correctly sized and balanced, typically lasts 30 years or more in a London property.
Book a sash cord repair
We repair and re-cord original sash windows across London and the Home Counties, with 15 years of experience on Victorian, Georgian and Grade II listed properties. Contact us for a free survey and a fixed quotation.