Sash Window Replacement Cost Calculator

Select window type, size, and glazing options to get an instant replacement cost estimate based on 2026 UK contractor rates.

Base Replacement Costs

Timber Sash Windows

Standard size (up to 1.2m × 1.5m): £900-£1,400 per window installed. Large size (over 1.2m × 1.5m): £1,200-£1,800. Price includes engineered hardwood (sapele, accoya, or iroko), factory spray finish, slim double glazing (24mm), stainless steel fittings, and 10-year guarantee. Made-to-measure lead time 4-6 weeks.

UPVC Sash Windows

Standard size: £600-£950 per window installed. Large size: £800-£1,200. Price includes multi-chambered UPVC frames, mock horn detailing, run-through sash horns, tilt function for cleaning, and A+ energy rating. Woodgrain foil finishes add £80-£140. Off-the-shelf sizes available next-day, bespoke 2-3 weeks.

Optional Upgrades

Double Glazing (+£200-£400)

Slim double glazed units (18-24mm overall depth) fit period sash boxes. U-value 1.4-1.8 W/m²K compared to 4.8 W/m²K for single glazing. Low-E coating and argon fill standard. Conservation-approved for listed buildings (subject to planning consent). Saves £120-£180 per year per window in heating costs.

Georgian Bars (+£150-£300)

Astragal glazing bars divide panes in traditional 2-over-2, 4-over-4, or 6-over-6 patterns. Factory-applied (not stuck-on grilles). Available in timber or UPVC. Georgian bars sit between double glazed panes or applied to outer surface. 25mm wide bars match Victorian originals, 20mm for Georgian properties.

Woodgrain Finish (+£80-£140, UPVC)

Foiled finish applied to UPVC frames mimics timber grain. Rosewood (mahogany tone), Irish Oak (golden brown), Golden Oak (honey oak), or Cream White. Matched to existing property woodwork. Factory-bonded foil, UV-stable, won't peel. Wipe-clean, no repainting needed.

When to Replace vs Repair

Replace your sash windows if:

• Timber rot affects more than 40% of the frame (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 (over £675-£1,050 in repairs)
• Property is not listed and you plan to sell within 10 years (buyers value new double glazing)

Repair your sash windows if:

• 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)
• You plan to keep the property 40+ years (restored timber lasts 80-120 years)
• Property value exceeds £800k (period features add 5-8% premium)

See our replacement cost guide and refurbishment cost guide for the full decision framework.

Sources

Replacement rates verified against:

• Checkatrade sash window replacement quotes (Jan 2026, 18 installers, London/Southeast)
• FENSA-certified installer pricing (Everest, Anglian, Safestyle, local independents, Jan 2026)
• Sash Window Workshop, The Sash Window Company, Sash Restoration published rates (Jan 2026)
• Timber window manufacturer trade price lists (Mumford & Wood, Masterframe, Accoya)