Sash Window Repair Guide

Most sash window problems can be repaired without full replacement, preserving historic fabric and saving money.

Quick answer: Traditional sash windows can be repaired rather than replaced in most cases. Common repairs like broken cords cost £80-150 per window, rot splicing £200-400, and draught-proofing £150-250. Full restoration runs £600-1,200 per window, still cheaper than replacement and preserving historic value.

Last reviewed: 15 June 2026 | 4 min read | Verified against 4 sources

Common sash window problems

Broken sash cords

The most common failure. Sash cords eventually wear through where they run over the pulley wheels. Symptoms: sash won't stay open, drops suddenly, or rattles. Repair involves accessing the weight pocket, removing the broken cord, and threading new cord (typically pre-stretched flax or modern nylon). Cost: £80-150 per window for professional work.

Stuck or painted-shut sashes

Windows painted shut over decades can be freed by carefully cutting the paint seal with a Stanley blade, then working the sash gently. Never force stuck windows as this can crack glazing or damage the frame. Professional easing and rebalancing: £60-100 per window.

Rotten timber

Bottom rails and sills suffer most from water ingress. Small areas of rot can be cut out and spliced with new matching timber. This is always preferable to replacement. Splice repairs: £200-400 depending on extent. Full sill replacement: £300-600.

Broken glazing

Replace like-for-like. Georgian windows used cylinder glass (hand-blown, with distortion) which adds character. Reproduction cylinder glass: £40-80 per pane. Modern float glass is cheaper but inappropriate for listed buildings.

Repair vs replacement decision

Historic England guidance is clear: repair is preferred. Replacement is only justified where:

More than 40% of the timber is decayed beyond repair
The frame has structural failure (not just cosmetic rot)
Original windows have been comprehensively replaced with poor-quality units

For listed buildings, replacement requires consent. Conservation officers typically insist on repair unless decay is extreme.

DIY vs professional repair

Broken cord replacement is within reach of competent DIYers. The SPAB publish a detailed technical guidance note on sash window repair. However, rot repairs require carpentry skills and matching timber. Draught-proofing systems need precise routing and installation.

Costs comparison

Repair costs (professional):

Cord replacement: £80-150 per window
Draught-proofing system: £150-250 per window
Rot splice repairs: £200-400
Full overhaul (cords, easing, draught-proofing, reglaze): £600-1,200

Replacement costs (like-for-like timber):

Box sash units: £1,800-3,500 per window including installation
Listed building consent fees: £206 (minor) or £407 (major)

Finding reputable contractors

The Master Craftsmen Register (Historic England) lists accredited sash window specialists. SPAB maintain a list of members offering conservation services. Avoid companies that lead with replacement rather than repair.

Historic England, "Traditional Windows: Their Care, Repair and Upgrading" (2017)
Society for the Protection of Ancient Buildings, "The Repair of Wood Windows" technical note
Building Conservation Directory, "Sash Window Repair Specialists"
Federation of Master Builders average pricing 2026