The Honest Answer
We manufacture replacement windows, so you might expect us to always recommend replacement. We do not. Some original sash windows are worth restoring — particularly early Georgian windows with handmade glass, or windows in Grade I and II* Listed buildings where the originals are part of the building's historic significance. For most Victorian and Edwardian sash windows, however, replacement offers better value, better performance, and a longer remaining lifespan.
When Restoration Makes Sense
Restoration involves stripping the existing sashes, repairing or splicing rotten timber, re-glazing, replacing cords and pulleys, draught-proofing, and repainting. A well-done restoration can extend the life of original windows by 15–25 years.
- Grade I or II* Listed buildings — where the planning authority requires retention of original fabric.
- Windows with historic glass — crown glass, cylinder glass, or early float glass with character and imperfections worth preserving.
- Budget constraints — restoring is cheaper per window if the frames are structurally sound.
- Minor issues only — if sashes are sound and only need draught-proofing and repainting.
When Replacement Is the Better Choice
- Significant rot — if more than 20% of the timber is affected, restoration costs approach replacement costs but with a shorter remaining lifespan.
- Single glazing — restored windows remain single-glazed unless slim double-glazed units are retrofitted (which adds significant cost).
- Thermal performance — new double-glazed sash windows achieve U-values of 1.4 W/m²K vs 4.8 W/m²K for restored single-glazed windows.
- Security — new windows include PAS24 multi-point locking as standard. Restored windows rely on original fitch fasteners.
- 50-year view — a new timber sash window lasts 60–100 years. A restored window may need further work in 15–25 years.
Cost Comparison
| Factor | Restoration | Replacement |
|---|---|---|
| Cost per window | £500 – £1,500 | £815 – £2,100 |
| Additional lifespan | 15 – 25 years | 60 – 100 years |
| Thermal performance | U-value 4.8 (single) | U-value 1.4 (double) |
| Security | Basic fitch lock | PAS24 multi-point |
| Energy bill saving | Minimal | £75 – £200/year |
| Planning permission | Rarely needed | Sometimes in Conservation Areas |
Over a 50-year horizon, replacement is almost always more cost-effective. The energy savings alone typically recover the price difference within 10–15 years, and you gain security, acoustic insulation, and zero maintenance for decades.
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