How to replace sash window cords

Video by Phil Novell. This walk-through draws on the video “Beginner’s Guide: Replace Your Sash Window Cords (Step-by-Step)” from Phil Novell, founder of Sash Window School and specialist restorer based in Surrey and London. The video is aimed at first-timers and explains the box frame anatomy clearly before getting into the practical steps — worth watching all the way through before you pick up a chisel.

1. Understand the box frame before you start

A traditional sash window box frame is hollow inside. Each side contains a concealed weight, connected to the sash by a cord that runs over a pulley at the top of the frame. The cord is attached to a groove along the side of the sash itself. When the cord breaks, the sash becomes unbalanced and difficult or impossible to use properly.

Most windows have two sashes — the lower (which you open most) and the upper. Both have their own cords and weights. When one cord breaks, it is sensible to replace all four cords at the same time, as they will all be roughly the same age and the others will not be far behind.

2. Remove the staff beads

The staff beads are the narrow timber mouldings running vertically down each side of the window frame inside the room, between the bottom sash and the frame. Carefully run a chisel or a flat pry bar down the edge of each bead to pop it away from the frame. Work gently — old beads can be brittle and it is useful to reuse them. If they split, you can replace them with matching moulding from a timber merchant.

Once both staff beads are off, the bottom sash can swing inward into the room. Support it from underneath as you ease it out, keeping the existing cords attached if possible so you can use them as a guide for the new ones.

3. Detach the cords from the sash

The cord fits into a groove along each side of the sash and is usually held with a single nail at the bottom of the groove. Carefully remove the nail and ease the cord out. You may find the cord is already parted — if so, the broken end will have dropped down through the pulley wheel and probably fallen into the weight pocket below.

Lower the sash gently onto a workbench or lay it flat on a dust sheet. Inspect the sash for damage while you have it out — it is much easier to repair any loose joints or paint the bottom rail now than when it is back in the frame.

4. Access the weight pockets

The weights live inside the hollow box frame, accessible through a small pocket piece in the lower part of each side of the frame. This is a small timber panel, sometimes painted over many times, screwed or wedged in place. Unscrew it or carefully lever it out. Inside you will find the cast iron weights — typically around 4 to 5 kg each, though it varies with the sash size.

Lift the weights out and cut away the old cord remnants. While the pocket is open, vacuum out any debris and check the inside of the box is clear of anything that would snag the new cord.

5. Thread the new cord over the pulley

Use proper waxed sash cord — a number 8 is the standard size for most domestic windows. Cut four lengths, each roughly 1.5 times the window height, and trim to exact length as you go. Thread a length of string or thin wire over each pulley first, then tie the sash cord to the string and pull it through. The cord needs to run smoothly over the pulley wheel; if the pulley is corroded or seized, replace it now while you have access.

Once through the pulley, drop the cord down into the weight pocket and tie it firmly to the weight. A clove hitch or a couple of half-hitches will hold; do not use a slip knot. Pull the cord gently upward to confirm the knot is holding before you continue.

6. Attach the cord to the sash and check the balance

Hold the weight up inside the pocket at its correct running position — about 50 mm from the bottom of the box. Mark the cord at pulley height, then cut it at a length that, when knotted into the sash groove, leaves the weight sitting about 50 mm above the pocket piece when the sash is fully open. This prevents the weight jamming at the bottom when you open the window.

Fix the cord into the groove in the sash with a nail through the knot. Do the same on both sides, then temporarily hold the sash in the frame to check the balance. It should rise and stay open at any position without effort on either side. If one side is heavier, adjust the cord length slightly.

7. Refit the pocket pieces and staff beads

Slide the weight pocket pieces back in and screw them home. Ease the sash back into the frame and test its movement before fitting the staff beads. The beads need to sit close enough to the sash to keep it running in the frame but not so tight that they bind. A whisker of clearance on each side is right — a playing card thickness as a gauge works well.

Tap the staff beads back in with a rubber mallet or pin them with panel pins. Fill any nail holes, sand and repaint the beads to match. A freshly roped sash window, sliding smoothly and staying exactly where you leave it, is genuinely one of the nicer things in an old house.

When to call a handyman

Call Richard if the frame itself is rotten or damaged, if the weights are cracked or missing, or if you have never done this before and the window is painted shut or otherwise awkward. Getting the cord lengths and weight balance right takes a bit of practice, and a poorly balanced sash will not stay open reliably no matter how new the cord is.