Draught-proofing windows and doors can cut heat loss by up to 20% and save around £60 a year on energy bills, according to the Energy Saving Trust (Energy Saving Trust, 2026). The most effective approach combines sealing gaps, upgrading glazing, and fitting thermal curtains.
The answer depends on your current windows and doors. If they are single-glazed or poorly fitted, simple draught-proofing measures, such as self-adhesive foam strips, silicone sealant, or brush strips, can make an immediate difference. For older double-glazed units, the seals may have degraded, and replacing them is often more effective than adding extra layers. Listed buildings or conservation areas may restrict external changes, but internal solutions like secondary glazing are usually permitted.
Seal gaps with draught-proofing strips
Gaps around window and door frames are the biggest source of draughts. Self-adhesive foam strips cost around £5–£10 per window and can be fitted in minutes, reducing heat loss by up to 15% (Energy Saving Trust, 2026). For doors, brush strips or threshold seals cost £10–£20 and block gaps at the bottom. Silicone sealant is better for fixed gaps between the frame and wall, costing roughly £5 per tube. All these materials are available at DIY stores and can be installed without professional help.
Add secondary glazing for single-glazed windows
Secondary glazing, an additional pane fitted inside the existing frame, can reduce heat loss through single-glazed windows by up to 65% (GOV.UK, 2026). DIY kits with magnetic or adhesive strips cost £20–£50 per window, while professional installation ranges from £200–£500 per window. Unlike replacement windows, secondary glazing does not require planning permission for most homes and can be removed in summer. It also reduces condensation and noise.
Upgrade to energy-efficient double glazing
Replacing single glazing with double glazing rated A++ (U-value below 1.2 W/m²K) can cut heating bills by around £195 per year for a typical semi-detached home (Energy Saving Trust, 2026). Costs vary by window size and material, but a standard uPVC double-glazed window costs £400–£600 installed. All new windows must meet Building Regulations Part L, which requires a minimum U-value of 1.4 W/m²K for windows (GOV.UK, 2026). For doors, composite or insulated doors with a U-value below 1.0 W/m²K are most efficient.
A worked example
Glazing is standard-rated for VAT at 20%. The zero rate for energy-saving materials covers insulation, heat pumps and solar panels; HMRC names secondary and double glazing as excluded (VAT Notice 708/6). The Energy Saving Trust estimates this combination saves approximately £195 per year on heating bills, giving a payback period of just over six years. Over 25 years, the total saving reaches nearly £4,900, even before factoring in rising energy prices. The Great British Insulation Scheme closed on 31 March 2026. It funded insulation measures only and never covered windows or glazing. Secondary glazing panels from a certified installer cost roughly £200–£400 per window and reduce heat loss by up to 65% according to the Energy Saving Trust. For the back door, a brush strip and letterbox cover add about £30. The table below summarises the figures for this scenario.
| Item | Figure |
|---|---|
| Upfront cost after grants | £1,200 |
| Yearly savings | £195 |
| Payback period | 6.2 years |
| 25-year lifetime savings | £4,875 |
What homeowners often get wrong
The most common mistake is assuming all window draughts need replacing the whole frame or glazing unit. Here are three frequent errors that cost homeowners time and money.
- Sealing trickle vents permanently Many people block ventilation slots thinking they stop draughts, but this traps moisture and causes mould. The right approach is to leave trickle vents open and seal only the moving parts of the sash or casement with foam strips, which avoids condensation damage and voided building warranties.
- Using expanding foam around door frames DIYers often fill large gaps with expanding foam, which can bow the frame and make the door stick. The correct method is to use silicone sealant for gaps under 5mm and timber fillets for larger spaces, preventing structural stress and a £150–£300 replacement door.
- Ignoring letterbox and keyhole draughts Homeowners draught-proof the door edges but forget the letterbox, which loses as much heat as a small window gap. Fitting a letterbox cover and keyhole draught excluder costs under £15 and saves around £15–£20 a year, a missed saving if overlooked.
Quick reference
- Self-adhesive foam strips cost £5–£10 per window and cut heat loss by up to 15% according to the Energy Saving Trust.
- Secondary glazing reduces heat loss by up to 65% and is permitted in most conservation areas without planning permission.
- Homes built before 2002 with single glazing may qualify for ECO4 funding covering full window replacement costs.
- Draught-proofing a typical semi-detached house costs around £200–£300 and pays for itself in two to three years.
- Never use expanding foam around door frames as it can warp the timber and invalidate the door warranty.
Frequently Asked Questions
Self-adhesive foam strips cost £5–£10 per window and reduce heat loss by up to 15%, according to the Energy Saving Trust.
Yes, internal secondary glazing is usually permitted in listed buildings or conservation areas, while external changes may be restricted.
Brush strips or threshold seals for doors cost £10–£20, according to the Energy Saving Trust, and can block gaps at the bottom.
