Sash window draught proofing what it costs, saves, and whether the payback works
If you live in a period home with sash windows, you will know the feeling of cold air seeping through gaps around the frame on a winter evening. The question homeowners most often ask is whether draught proofing those windows is a genuine energy saving measure or just a comfort upgrade.
Professional sash window draught proofing costs £150 to £300 per window and saves £4 to £10 a year on heating. The main benefit is eliminating draughts and reducing condensation, not financial payback.
- Professional draught proofing costs £150 to £300 per window.
- Annual energy saving is 15 to 30 kWh per window.
- Payback period is 15 to 40 years based on gas heating.
- 78% of homeowners report draught reduction as main benefit.
- DIY kits cost £10 to £40 per window from builders' merchants.
- Sash window draught proofing what it costs, saves, and whether the payback works
- What draught proofing a sash window actually costs in 2026
- Quick numbers cost, saving, U-value, and payback table
- How much energy and money a sealed sash window actually saves
- Which sash windows can be draught proofed — and which cannot
- How to install draught proofing — professional vs DIY
- Who can do the work — MCS, TrustMark, and certification rules
- Is draught proofing worth it — the direct answer for most homeowners
The direct answer is this. Professional draught proofing of a standard sash window costs £150 to £300 per window and saves roughly £4 to £10 per year on heating bills, giving a payback period of 15 to 40 years. The real benefit is not financial — it is the elimination of draughts and a reduction in condensation, which 78% of homeowners who have done the work report as the main reason they are satisfied (Energy Saving Trust, 2026).
What draught proofing a sash window actually costs in 2026
Professional draught proofing for a single sash window costs between £150 and £300 including materials and labour, according to the Energy Saving Trust’s 2026 cost guide (Energy Saving Trust, 2026). DIY brush-strip and foam-seal kits cost £10 to £40 per window from builders’ merchants or online retailers.
Secondary glazing for sash windows is a separate product and costs £150 to £500 per window — it improves the U-value of the glass itself, whereas draught proofing only seals gaps around the frame. Costs also vary by region. London and the South East typically run 20 to 30% higher than the UK average, according to the Checkatrade 2026 price survey (Checkatrade, 2026). If the sash window also needs repairs such as broken cords or rotten timber, add £100 to £400 per window.
Quick numbers cost, saving, U-value, and payback table
| Item | Figure | Source |
|---|---|---|
| Professional draught proofing cost (per window) | £150–£300 | EST 2026 cost guide |
| DIY draught proofing cost (per window) | £10–£40 | DIY stores 2026 pricing |
| Annual energy saving (per window) | 15–30 kWh | DESNZ energy savings calculator |
| Annual cost saving (per window, gas-heated home) | £4–£10 | DESNZ / Ofgem 2026 fuel price cap |
| U-value improvement (from ~5.7 to ~4.5 W/m²K) | 20–25% reduction | EST window U-value database |
| Payback period (professional install, gas heating) | 15–40 years | Calculated from above |
| Payback period (DIY install, gas heating) | 2–5 years | Calculated from above |
How much energy and money a sealed sash window actually saves
A single-glazed sash window has a typical U-value of 5.7 W/m²K. Draught proofing reduces this to around 4.5 W/m²K, a 20 to 25% improvement in heat loss through the frame area (Energy Saving Trust, 2026). The energy saving per window is 15 to 30 kWh per year — roughly the electricity used by a tumble dryer for three to five cycles.
For a typical gas-heated home on the 2026 price cap of 6.3p per kWh, that works out at £0.95 to £1.89 saved per window annually (Ofgem, 2026). For an electric-heated home at 24.5p per kWh, the saving is £3.68 to £7.35 per window annually. The biggest saving is not financial — it is reduced draughts and fewer condensation problems. A 2026 Energy Saving Trust survey found 78% of homeowners who draught-proofed sash windows reported fewer drafts as the main benefit (Energy Saving Trust, 2026).
Which sash windows can be draught proofed — and which cannot
Most timber sash windows built before 2000 can be draught proofed, provided the frame is sound and not rotten. uPVC sash windows, common from the 1990s onwards, often have built-in weather seals — additional draught proofing is rarely needed or effective. Sash windows with original sash cords, weights, and pulleys can be draught proofed without removing the window.
Windows with severe rot, broken glass, or missing sash cords must be repaired first — draught proofing over damage is ineffective, according to the Glass and Glazing Federation’s 2026 guidance (GGF, 2026). Listed buildings and conservation areas may require listed building consent or planning permission for draught proofing. Check with your local authority before starting work (Historic England, 2026).
How to install draught proofing — professional vs DIY
Professional installation involves a survey, then fitting brush-pile seals into the sash channels, meeting stiles, and the bottom rail. It typically takes one to two hours per window. DIY kits use self-adhesive foam strips (low cost, short life) or brush-pile strips (higher cost, longer life) — installation takes 30 to 60 minutes per window.
For DIY, the key steps are: clean the frame, measure gaps, cut strips to length, press into place, and test the sash operation (Energy Saving Trust, 2026). Professional installation costs five to ten times more but lasts 10 to 15 years. DIY foam strips last one to three years, while brush-pile lasts three to five years. Both methods reduce draughts but do not change the U-value of the glass itself — secondary glazing is needed for that.
Who can do the work — MCS, TrustMark, and certification rules
For professional draught proofing, there is no mandatory certification scheme, unlike heat pumps or solar panels. TrustMark-registered tradespeople are recommended for consumer protection (TrustMark, 2026). The Microgeneration Certification Scheme (MCS) does not apply to draught proofing — it covers renewable energy installations only.
Gas Safe Register, FENSA, and NICEIC or NAPIT are not relevant for draught proofing work. If the work is part of a larger energy efficiency project, such as with a heat pump, check whether the installer holds PAS 2035 accreditation for whole-house retrofit (DESNZ, 2026).
Is draught proofing worth it — the direct answer for most homeowners
For most homes, sash window draught proofing is not a cost-effective energy saving measure — it has a payback of 15 to 40 years for professional installation. It is worth doing for comfort reasons: it stops cold draughts and reduces condensation, which can damage paintwork and timber. If you do it yourself with a £20 kit, payback is two to five years, making it a reasonable DIY project.
For listed buildings or homes in conservation areas, draught proofing is often the only permitted energy improvement without full consent. The best financial use of your money for sash windows is to repair the window first, then draught-proof, then consider secondary glazing if further improvement is wanted. Compare sash window draught proofing costs with secondary glazing options Check whether your home is eligible for ECO4 energy efficiency grants
Frequently Asked Questions
Professional draught proofing costs £150 to £300 per window according to the Energy Saving Trust's 2026 cost guide. DIY kits cost £10 to £40 per window.
It saves £4 to £10 per year per window on heating bills according to the DESNZ energy savings calculator. The main benefit is draught reduction and less condensation.
Yes for comfort but not for financial payback. The payback period is 15 to 40 years. 78% of homeowners are satisfied because it stops draughts and reduces condensation (Energy Saving Trust, 2026).
Yes, DIY brush-strip and foam-seal kits cost £10 to £40 per window. They are effective for sealing gaps around the frame if the window is in good condition.
Yes, sealing gaps reduces cold air ingress and helps balance indoor humidity. This lowers the risk of condensation on the glass and surrounding frame.
