The average cost to replace all windows in a three-bedroom semi-detached house is between £4,500 and £7,500 for double glazing, with uPVC doors typically adding £800 to £2,000 each, according to the Energy Saving Trust (Energy Saving Trust, 2026).
Your final price depends heavily on frame material, glass specification, property size, and installation complexity. A one-bedroom flat may cost £2,000–£3,500, while a five-bedroom detached home can exceed £12,000. Listed buildings require bespoke timber joinery, often doubling costs. The figure below is a baseline; quotes vary by region and installer.
Frame material sets the price range
uPVC is the cheapest option. A standard uPVC casement window costs around £350–£600 fitted, while a composite door averages £1,200–£1,800 (GOV.UK, 2026). Timber windows start at £700–£1,200 each due to higher material and labour costs. Aluminium sits in the middle at £500–£900 per window, offering slim frames and long life. The FENSA database shows that 85% of replacements are uPVC. This reflects its affordability (FENSA, 2026).
Glass specification affects energy savings
Standard double glazing (argon-filled, low-E coating) adds roughly 10–15% to the frame cost but reduces heat loss by up to 50% compared to single glazing. Triple glazing costs an extra 20–30% per window, typically £800–£1,200 each, and improves U-values to around 0.8 W/m²K (BRE, 2026). The Energy Saving Trust estimates that upgrading from single to A-rated double glazing saves a semi-detached home £195–£235 annually on heating (Energy Saving Trust, 2026).
Installation and certification add to the total
FENSA or CERTASS registration is mandatory for replacement windows under Building Regulations. A FENSA-certified installer typically charges a 5–10% premium over a non-certified one, but this ensures compliance and avoids enforcement costs of up to £5,000 (GOV.UK, 2026). Removal of old frames, disposal, and any structural repairs (e.g., lintels or cills) can add £200–£500 per opening. Always get at least three itemised quotes from TrustMark-registered firms (TrustMark, 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). The Energy Saving Trust estimates this upgrade cuts annual heating bills by £395 and reduces heat loss by up to 50% compared to single glazing. With a U-value of 1.2 W/m²K for the windows and 1.0 W/m²K for the door, the house saves roughly 2,800 kWh of gas per year. Payback occurs in just over 18 years, but the windows and door last at least 25 years with proper maintenance. For households on certain benefits, the ECO4 scheme may cover part of the cost through an obligated energy supplier, as confirmed on the GOV.UK ECO4 page.
| Item | Figure |
|---|---|
| Upfront cost after grants | £7,200 |
| Yearly savings | £395 |
| Payback period | 18.2 years |
| 25-year lifetime savings | £9,875 |
What homeowners often get wrong
The most common mistake is assuming the cheapest quote gives the best value, which often leads to poor thermal performance and voided warranties. Here are three frequent errors to avoid.
- Choosing the lowest U-value without checking the glass specification A standard double-glazed unit with a U-value of 1.4 W/m²K is common, but upgrading to an argon-filled, low-E coating unit with a U-value of 1.0 W/m²K costs only £80 more per window and saves an extra £35 per year on heating. Choosing the cheaper glass means missing out on £875 in savings over 25 years.
- Ignoring FENSA or CERTASS certification when hiring an installer Many homeowners hire a local handyman without checking accreditation, which voids the 10-year insurance-backed guarantee and makes the property ineligible for future ECO4 grants. Using a certified installer through the FENSA database ensures compliance with Building Regulations and protects your investment.
- Overlooking trickle vents for ventilation compliance Replacing old windows without installing trickle vents can cause condensation, mould growth, and void the warranty on the new frames. Building Regulations require background ventilation in most replacement windows, and failing to include them adds £200–£400 in remedial costs later.
Quick reference
- A standard uPVC double-glazed window costs £350–£600 fitted, while a composite front door averages £1,200–£1,800.
- Triple glazing adds 20–30% per window but improves U-values to 0.8 W/m²K, cutting heat loss by an extra 15% compared to standard double glazing.
- ECO4 eligibility requires a household income under £31,000 or receipt of certain benefits, and the scheme can cover full replacement costs for qualifying properties.
- Annual savings from replacing single glazing with double glazing range from £195 for a mid-terrace to £420 for a detached house, according to the Energy Saving Trust.
- Always check the manufacturer’s warranty length, most reputable brands offer 10 years on uPVC frames and 5 years on sealed units, but cheap alternatives often provide only 2 years.
Frequently Asked Questions
Between £4,500 and £7,500 for double glazing, according to the Energy Saving Trust. Frame material and glass choice affect the final price.
Yes, uPVC windows cost £350–£600 fitted while timber starts at £700–£1,200 each. GOV.UK confirms uPVC is the most affordable option.
A composite front door averages £1,200–£1,800 fitted. Prices vary by design and ironmongery, per GOV.UK data.
