How many sash cords does each window need?

Each traditional sash window needs 4 cords — 2 for the upper sash and 2 for the lower sash. Each cord connects from the sash through a pulley at the top of the frame to a lead or iron counterbalance weight in the box frame. When one cord breaks, it is advisable to replace all four to ensure even operation.

How do I calculate sash window weight?

Measure the sash dimensions and glass thickness. Glass weighs approximately 2.5 kg/m² per mm of thickness (so 4mm glass = 10 kg/m²). Add 3-4 kg for the timber frame of each sash. The two counterbalance weights for each sash should together equal the sash weight. Standard lead weights are 1-3 kg each.

What type of sash cord should I use?

Use pre-stretched waxed cotton sash cord (No.4 or No.6) for traditional windows. No.4 (6mm) suits most domestic sashes; No.6 (8mm) for heavier sashes. Synthetic (nylon) cord is cheaper but stretches and can slip on pulleys. Never use ordinary string or rope — it will stretch, fray, and break quickly.

How do I improve draughts on sash windows?

Install brush-pile or rubber draught strip in channels routed into the frame and meeting rails. This reduces draughts by up to 80% while still allowing the sashes to slide. Staff bead draught strip seals the inner sash against the frame. Parting bead strip seals between the two sashes. Professional systems like the Ventrolla perimeter sealing system are highly effective.

What is the difference between staff bead and parting bead?

Staff bead is the inner moulding that holds the lower sash in place — it runs up both sides and across the bottom of the frame. Parting bead sits in a groove between the two sashes, keeping them in separate channels. Both can be replaced to improve the fit and reduce draughts. They are removed to access the sashes for cord replacement.

TradeCalculator

Sash Window Repair Calculator

Calculate sash cords (4 per window), counterbalance weights by sash weight, draught strip and staff/parting bead for sash window repair.

Number of Windows

Sash Height

Height of each sash

Sash Width

Width of each sash

Replace all cords

Recommended: replace all 4 per window

Include draught strip

Brush pile or rubber seal

Replace staff bead

Inner frame moulding

Price Per Cord Set (optional)

Set of 4 cords per window

Price Per Weight (optional)

How We Calculate This

This calculator determines the materials needed for sash window repair: cords, counterbalance weights sized to sash weight, draught stripping, and replacement beading.

The formula

Cords = 4 per window (2 per sash)
Sash weight = Glass area × (thickness × 2.5 kg/m²) + ~3.5 kg frame
Weight each = Sash weight ÷ 2
Draught strip = Sash perimeter × 2 sashes

Repair tips

Replace all 4 cords at once, even if only one is broken
Wax the pulleys and channels for smooth operation
Mark sash positions before removal for accurate refitting
Check the weight pockets for debris before reinstalling

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.