Sash Window Replacement Cost Guides

Replace when timber rot exceeds 40%, box frames are collapsed, or you want modern thermal performance. Replacement costs £600-£2,200 per window depending on material, glazing, and period detailing.

Replacement Guides by Material and Style

Replacement vs Repair Decision

Replace your sash windows when:

• Timber rot exceeds 40% of frame volume (uneconomical to repair)
• Box frame is rotten or collapsed (repair costs £800-£1,500 per window)
• You want modern thermal performance (U-value under 1.8 W/m²K, repair achieves 2.4-3.2)
• Total repair cost exceeds 75% of replacement cost
• Property is not listed and you plan to sell within 10 years

Consider repair instead when:

• Listed building or conservation area front elevation (like-for-like required)
• Original features intact (glazing bars, shutters, weights, pulleys)
• Timber rot under 30% (splice repairs cost £150-£350 per sill/rail)
• Property value exceeds £800k (period features add 5-8% premium)

See our refurbishment cost guide for the full repair vs replace decision framework.