Window Restoration vs Replacement: The Complete UK Homeowner's Guide

Yes. Professional draught-proofing using brush pile seals fitted into the staff beads and parting beads can reduce air leakage by up to 86%. The seals are virtually invisible when the window is closed and allow smooth sash operation. Combined with weather stripping at the meeting rail and a sprung seal at the sill, a draught-proofed sash window performs comparably to a modern casement window for air-tightness.

Possibly. Many conservation areas have Article 4 Directions that remove permitted development rights for window replacement, meaning you need planning permission. Even without an Article 4 Direction, replacement windows that materially affect the character of the building may require consent. Always check with your local planning authority before ordering replacement windows. For listed buildings, Listed Building Consent is always required.

A comprehensive sash window restoration — including timber repairs, cord replacement, draught-proofing, and full redecoration — typically lasts 15-25 years before the next overhaul is needed. The draught-proofing seals may need replacing after 8-12 years, and the paint finish may need refreshing after 8-10 years on exposed elevations, but the structural work should endure for two decades or more.

Yes, and it should be wherever possible. Original crown glass and cylinder glass has a distinctive character — slight waviness, small bubbles, and variations in thickness — that is impossible to replicate with modern float glass. A skilled restoration specialist will carefully remove and re-glaze original panes using traditional linseed oil putty. Only cracked or broken panes need replacing.

Repair addresses specific faults — a broken cord, a misted sealed unit, or a rotten section of timber. Restoration is a comprehensive overhaul of the entire window to bring it back to full working order with improved performance. Restoration includes all necessary repairs plus draught-proofing, rebalancing, full timber treatment, and complete redecoration. Think of repair as fixing what is broken and restoration as rejuvenating the whole window.

Secondary glazing does not quite match the thermal performance of modern double glazing, but it comes closer than many people expect. A good secondary glazing system achieves an effective U-value of approximately 1.8-2.0 W/m²K, compared to 1.2-1.4 for standard double glazing. For noise reduction, secondary glazing actually outperforms standard double glazing because the wider air gap (typically 100mm+) is more effective at absorbing sound waves.

In some cases, yes. Slim-profile vacuum-sealed double glazed units (as thin as 6mm) can be fitted into existing sash window rebates, provided the sashes and frames are structurally sound and the rebate depth is sufficient. However, the added weight of double glazing requires rebalancing the sash weights and may stress older frames. This is a specialist job and not suitable for all windows.

Look for members of the Guild of Master Craftsmen, the Federation of Master Builders, or specialists recommended by your local conservation officer. Check for specific experience with your window type (Georgian six-over-six, Victorian two-over-two, etc.) and ask to see examples of previous work. Avoid companies that only sell replacement windows, as they have a commercial incentive to recommend replacement over restoration.

Draught-proofing alone can improve an EPC rating by 1-3 points. Adding secondary glazing can deliver a further 5-10 point improvement. However, the EPC assessment methodology tends to favour double glazing over single glazing with secondary glazing, even when real-world performance is similar. If maximising your EPC rating is the primary goal, replacement double glazing will score better on the assessment, even though restoration with secondary glazing may deliver comparable real-world comfort.

For period properties, the most cost-effective approach is often a combination: full restoration with draught-proofing for windows in good condition, targeted replacement for windows beyond economical repair, and secondary glazing for rooms where thermal or acoustic performance is a priority (bedrooms, living rooms). This mixed approach preserves character where it matters most while being pragmatic about windows that cannot be saved.