Double glazed windows are expensive because the average cost for a standard uPVC double-glazed window installed in 2026 is £400–£600, with premium timber or aluminium options reaching £1,000–£1,500 per window, driven by materials, manufacturing complexity, and installation requirements (Energy Saving Trust, 2026).
The price you pay depends heavily on frame material, glass specification, and the number of openings. A fixed casement window costs less than a tilt-and-turn unit. Heritage or listed-building consent adds survey and bespoke fabrication fees. Energy performance standards, such as a whole-window U-value of 1.4 W/m²K or lower, require advanced low-emissivity coatings and argon gas fills, which increase production costs.
Frame materials dictate the base price
uPVC is the cheapest option at £400–£600 per window, but composite and aluminium frames cost £700–£1,200, and timber frames start at £1,000, according to the Energy Saving Trust (Energy Saving Trust, 2026). Timber requires regular painting and treatment, adding long-term maintenance costs. Aluminium frames are strong and slim but need thermal breaks to meet Building Regulations Part L, which pushes up the unit price. The frame accounts for roughly 40–50% of the total window cost.
Glass technology and glazing specifications add cost
Standard double glazing uses two 4mm panes with a 12–16mm argon-filled gap, but high-performance versions include low-E coatings, warm-edge spacer bars, and laminated or toughened glass. A coated, gas-filled unit can cost 20–30% more than a basic one, yet it achieves a U-value of 1.2 W/m²K instead of 2.0 W/m²K (BRE, 2026). Triple glazing, three panes with two gas gaps, is another step up, adding roughly £150–£250 per window but offering U-values below 0.8 W/m²K. Acoustic glass for noise reduction or solar-control glass for overheating protection also raises the price.
Installation and labour are a significant portion
Professional installation typically accounts for 30–40% of the total cost, including removal of old windows, disposal, making good internal and external finishes, and sealing to prevent drafts and water ingress. FENSA-registered installers must certify compliance with Building Regulations, which adds administrative overhead (FENSA, 2026). Complex jobs, such as windows on upper floors, large bespoke sizes, or properties with non-standard openings, require more time and scaffolding, increasing labour to £200–£400 per window. Replacing all windows in a three-bedroom house typically costs £4,000–£8,000 including installation.
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 upgrade cuts annual heating bills by £235 and reduces heat loss by 1,500 kWh per year. With a £7,500 BUS grant this household would not qualify for that specific scheme, but they may be eligible for ECO4 funding if they receive means-tested benefits. The payback period on the net cost of £5,500 is roughly 23 years based on current energy prices. Over a 25-year window lifespan the total savings reach £5,875, meaning the investment nearly pays for itself. The whole-window U-value for modern double glazing sits at 1.2 W/m²K, well below the 4.8 W/m²K typical of single glazing.
| Item | Figure |
|---|---|
| Upfront cost after grants | £5,500 |
| Yearly savings | £235 |
| Payback period | 23 years |
| 25-year lifetime savings | £5,875 |
What homeowners often get wrong
The most common mistake is buying the cheapest double glazing without checking the energy performance ratings. Below are three frequent errors that cost UK homeowners money and comfort.
- Assuming all double glazing is the same Many buyers choose budget uPVC windows with a U-value of 1.6 W/m²K, thinking they will perform identically to premium units. A window with a U-value of 1.2 W/m²K saves an extra £50 per year on heating, which adds up to £1,250 over a 25-year lifespan.
- Ignoring installation quality Homeowners focus on the window price and overlook the installer’s competence. Poor fitting with gaps around the frame can increase heat loss by 20%, wasting £47 per year and potentially voiding the manufacturer’s warranty.
- Skipping the FENSA or CERTASS certificate Some households hire an unregistered fitter to save £200 upfront. This mistake means the installation does not comply with Building Regulations Part L, which can cause problems when selling the house and may lead to enforcement action from the local council.
Quick reference
- A standard uPVC double-glazed window costs £400–£600 installed in 2026, according to the Energy Saving Trust.
- Timber and aluminium frames can reach £1,000–£1,500 per window, with timber requiring repainting every 5–7 years.
- ECO4 funding covers double glazing for households on means-tested benefits, but the property must have an EPC rating of E, F, or G.
- 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).
- Installing double glazing without a FENSA or CERTASS certificate can invalidate your house insurance and delay a property sale.
Frequently Asked Questions
Double glazed windows cost more because they include two glass panes, argon gas fills, and low-E coatings for energy efficiency. The Energy Saving Trust states that manufacturing and installation add £200–£1,000 per window over single glazing.
A standard uPVC double glazed window costs £400–£600 installed, while timber or aluminium options range from £700 to £1,500 per window, according to the Energy Saving Trust.
Yes, double glazed windows can save you £130–£200 a year on energy bills, based on Ofgem figures. The Energy Saving Trust confirms they also reduce condensation and noise. That makes them a long-term investment.
