Sash Window Energy Efficiency Guides

Draughty single-glazed sash windows lose 10-15% of household heat. Draught proofing saves £60-£120 per window per year, double glazing saves £120-£180. Payback periods 1.8-7 years.

Energy Efficiency Guides

Energy Efficiency Options Compared

Which Energy Upgrade Should You Choose?

Draught Proofing (£140-£280 per window)

Best for: properties where you plan to keep the original single glazing, listed buildings, budget-conscious owners. Reduces heat loss by 25-50% for minimal cost. Shortest payback period (1.8-2.8 years). Can be combined with secondary glazing or double glazing later.

Pros: Lowest cost, DIY-friendly, reversible, approved for listed buildings, immediate comfort improvement, noise reduction.

Cons: Doesn't improve thermal performance as much as double glazing, seals wear out after 8-20 years.

Secondary Glazing (£400-£600 per window)

Best for: listed buildings where double glazing not permitted, properties with period glass to preserve, noise reduction priority. Creates air gap between panes. U-value 1.8-2.2 W/m²K (vs 4.8 single glazed). Removable for summer ventilation.

Pros: Reversible, preserves original windows, excellent noise reduction, approved for listed buildings, good thermal performance.

Cons: Two sets of windows to clean, reduces light slightly, not as thermally efficient as double glazing.

Slim Double Glazing Retrofit (£800-£1,200 per window)

Best for: non-listed properties, owners keeping property 10+ years, maximising energy efficiency. Replace single glazing with 18-24mm double glazed units in existing sashes. U-value 1.4-1.8 W/m²K. Saves £120-£180 per year per window.

Pros: Best thermal performance, low maintenance, single set of windows, modern comfort, adds property value.

Cons: Longer payback period (4.4-10 years), not reversible, may need planning consent in conservation areas, heavier sashes may need weight adjustment.

Full Double Glazed Replacement (£900-£2,200 per window)

Best for: windows beyond repair, modern thermal performance wanted, property not listed. New timber or UPVC sashes with factory-fitted double glazing. U-value 1.2-1.6 W/m²K. See our replacement guides.

ECO4 and Green Home Grants

ECO4 scheme funds energy-efficient window improvements for eligible households (income under £31,000 or on benefits). Grants cover £600-£1,800 per window for double glazing replacement. Listed buildings and conservation area properties can apply to Historic England or local heritage schemes for draught proofing grants.

Check eligibility via Simple Energy Advice or gov.uk/improve-energy-efficiency.

Building Regulations and Planning

Draught proofing and like-for-like single glazing replacement: no planning permission or Building Regulations approval needed.

Double glazing in conservation areas or listed buildings: requires planning consent and listed building consent. Must demonstrate heritage benefit or minimal visual impact. Slim double glazing (18-24mm) more likely to be approved than standard 28mm units.

Consult your local conservation officer before starting work. Historic England guidance: "Repair and draught-proof first, secondary glazing second, slim double glazing third, full replacement last resort."