Large double glazed windows typically cost between £600 and £2,500 per window, including installation, depending on size, frame material and glazing type, according to the Energy Saving Trust (Energy Saving Trust, 2026). A standard 1.2m x 1.2m double glazed window averages around £800, but a large 2m x 2m window can reach £1,800 to £2,500.
The exact cost depends on whether the window is a fixed pane, casement or sash style, and the frame material, uPVC is cheapest, timber is most expensive. These figures assume a standard double glazing unit (argon-filled, low-E coating) with a U-value of around 1.2 W/m²K. Larger windows require stronger frames and thicker glass, raising both material and labour costs. Prices also vary by region and installer, so always get at least three quotes.
Frame material drives the final price
uPVC frames are the most budget-friendly, costing £600–£1,200 for a large window, while aluminium frames range from £900–£1,800. Timber frames are the priciest, at £1,200–£2,500 for a large unit, according to the Energy Saving Trust (Energy Saving Trust, 2026). Composite frames fall in the middle, at £800–£1,500. Frame material also affects thermal performance, aluminium and timber can achieve lower U-values than uPVC when properly designed, but cost more upfront.
Larger windows need stronger glass and framing
For windows over 2m², toughened or laminated safety glass is often required under building regulations (Gov.uk Approved Document K, 2026). This adds £100–£300 per window. Also, larger panes may need reinforced frames or additional structural support, which adds £150–£400 to installation costs. Triple glazing is an option for large windows, costing £200–£500 extra per unit but improving U-values to around 0.8 W/m²K.
Installation and fitting costs add significantly
Installation for a large double glazed window typically costs £200–£500, depending on access and complexity. A full frame replacement (including removing the old window and making good) costs £300–£700, according to TrustMark (TrustMark, 2026). If the opening needs enlarging, costs rise by £500–£1,500. Always use a FENSA-registered installer to comply with building regulations (FENSA, 2026).
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). This figure assumes timber frames from a FENSA-registered installer, costing £2,200 per window. With the windows replacing single-glazed originals, the Energy Saving Trust estimates annual heating savings of roughly £195 per year on a gas-heated home (Energy Saving Trust). The payback period stretches to around 19 years, but the 25-year lifetime savings total approximately £4,875, not counting the added property value and improved comfort. If the homeowner qualifies for ECO4 (e.g., receiving means-tested benefits), a grant could cover part of the installation cost, shortening the payback significantly.
| Item | Figure |
|---|---|
| Upfront cost after grants | £3,800 |
| Yearly savings | £195 |
| Payback period | 19 years |
| 25-year lifetime savings | £4,875 |
What homeowners often get wrong
The most common mistake is assuming all large double glazed windows cost the same, regardless of frame material and style. This leads to three frequent errors that cost homeowners money and performance.
- Choosing the cheapest frame without checking U-values Many homeowners pick uPVC for its low upfront cost, unaware that a poorly designed uPVC frame can have a U-value above 1.4 W/m²K, losing heat faster than a timber or aluminium frame with a U-value of 1.0 W/m²K. This mistake can add £50 to £100 to yearly heating bills for a large window.
- 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). This oversight adds 20% to the labour cost, roughly £200 on a £1,000 installation, and the homeowner cannot reclaim it later.
- Assuming all large windows qualify for the BUS grant The Boiler Upgrade Scheme only covers heat pumps and biomass boilers, not windows. Homeowners who spend £7,500 on windows expecting a BUS grant end up with no subsidy. The correct route is ECO4 for low-income households or a local authority grant.
Quick reference
- A large 2m x 2m double glazed window costs between £1,200 and £2,500 installed, with timber frames at the top end.
- uPVC frames for large windows are the cheapest option at £600 to £1,200, but aluminium frames offer better thermal performance for £900 to £1,800.
- ECO4 eligibility requires the homeowner to be on a means-tested benefit and the property to have an EPC rating of D or below.
- Replacing single glazing with double glazing on a large window saves roughly £100 to £195 per year in heating costs, according to the Energy Saving Trust.
- Installing large double glazed windows without a FENSA certificate can void your building regulations compliance and reduce your home’s resale value.
Frequently Asked Questions
A large double glazed window costs £600–£2,500 installed, according to the Energy Saving Trust. The price varies by frame material, with uPVC cheapest and timber most expensive.
A 2m x 2m double glazed window typically costs £1,800–£2,500 installed. This assumes a standard argon-filled unit with a U-value of around 1.2 W/m²K.
Yes, large windows cost more due to stronger frames and thicker glass. Building regulations may require toughened or laminated safety glass for windows over 2m², adding £100–£300.
