Typical cost of aluminium casement windows starts at £450 per window fitted
The national average for a standard 600mm x 1200mm opening casement, supplied and installed, begins around £450 per window. This figure is drawn from the Energy Saving Trust’s replacement windows cost guide for 2026 (Energy Saving Trust, 2026). For larger or multi-pane configurations, prices rise to between £650 and £900 per window. Triple-glazed options typically add 20% to 30% to the base figure.
Aluminium casement windows cost £450 to £900 per window fitted in 2026, depending on size and glazing. Triple-glazed options add 20-30% to the price. Compare quotes from certified installers.
- Cost starts at £450 per standard 600x1200mm window fitted.
- Triple-glazed aluminium casements add 20-30% to base cost.
- London and South East prices are 15-20% above UK average.
- Double-glazed U-values range from 1.4 to 1.6 W/m²K.
- Great British Insulation Scheme does not cover window replacements.
- Typical cost of aluminium casement windows starts at £450 per window fitted
- Aluminium casement windows achieve a U-value between 1.2 and 1.6 W/m²K
- Eligibility for the Great British Insulation Scheme does not cover window replacements
- The Energy Company Obligation (ECO4) provides grants for windows only in specific circumstances
- Quick numbers for aluminium casement windows
- Aluminium casement windows are eligible for the Home Upgrade Grant (HUG2) only in off-gas-grid homes
- How to verify an aluminium casement window installer is certified
- Aluminium casement windows are a 'like-for-like' replacement under permitted development rights
Regional variation is significant. London and the South East command prices 15% to 20% higher than the UK average, while Scotland and the North East are often 5% to 10% lower, according to the Department for Energy Security and Net Zero (DESNZ) regional cost indices (DESNZ, 2026). All figures exclude VAT at 20%, the standard rate for replacement windows unless the work is part of a wider renovation qualifying for reduced-rate VAT.
Aluminium casement windows achieve a U-value between 1.2 and 1.6 W/m²K
Double-glazed aluminium casements with a thermal break typically achieve U-values of 1.4 to 1.6 W/m²K. This meets the current requirement in Building Regulations Approved Document L, 2025 edition, Table 6.2, which sets a maximum U-value of 1.6 W/m²K for replacement windows installed in 2026 (Approved Document L, 2025). Triple-glazed versions with argon fill and warm-edge spacers reach 1.2 to 1.4 W/m²K, exceeding the minimum standard.
Actual thermal performance depends on glass specification, frame design, and installation quality. Installers certified under the Microgeneration Certification Scheme (MCS) must guarantee stated U-values under the MCS 023 standard (MCS 023, 2026). You can request a certified U-value certificate before ordering.
Eligibility for the Great British Insulation Scheme does not cover window replacements
The Great British Insulation Scheme (GBIS) funds cavity wall, loft, and solid wall insulation only. It explicitly excludes window or door replacements, as confirmed on the GOV.UK page for eligible measures (GOV.UK, 2026). Homes with an Energy Performance Certificate (EPC) rating of D or below may qualify for GBIS, but the scheme will not reduce the cost of new windows.
The Energy Company Obligation (ECO4) provides grants for windows only in specific circumstances
ECO4 can fund replacement windows, but only for low-income, vulnerable households where the existing windows are single-glazed or have a U-value above 3.0 W/m²K. This is detailed in the Ofgem ECO4 Guidance, Delivery v5.0 (Ofgem, 2026). The property must have an EPC rating of E, F, or G at the time of application. Windows are funded as part of a whole-house improvement plan, not as a standalone measure.
The maximum grant per window is capped at £750 under ECO4, but only when installed by an MCS-certified contractor, as per the Ofgem ECO4 Measure Costs table (Ofgem, 2026). If your home does not meet these criteria, you will not receive ECO4 funding for windows.
Quick numbers for aluminium casement windows
| Item | Typical figure | Source |
|---|---|---|
| Cost per window (standard 600x1200mm) | £450–£650 | EST “Replacement Windows Cost Guide” (2026) |
| Cost per window (large/multi-pane) | £650–£900 | EST “Replacement Windows Cost Guide” (2026) |
| U-value (double-glazed) | 1.4–1.6 W/m²K | Approved Document L (2025) |
| U-value (triple-glazed) | 1.2–1.4 W/m²K | Approved Document L (2025) |
| ECO4 maximum grant per window | £750 | Ofgem “ECO4 Measure Costs” (2026) |
| Typical lifespan | 30–45 years | British Fenestration Rating Council (BFRC) data (2026) |
Compare aluminium casement windows with uPVC alternatives
Aluminium casement windows are eligible for the Home Upgrade Grant (HUG2) only in off-gas-grid homes
The Home Upgrade Grant phase 2 (HUG2) funds energy-efficiency improvements, including window replacements, for off-gas-grid homes with an EPC rating of D or below. This is set out in the DESNZ Home Upgrade Grant Phase 2 Guidance (DESNZ, 2026). Eligible homes must be in England. Scotland, Wales, and Northern Ireland have separate schemes, such as Nest and Warm Homes.
The grant covers up to 100% of costs for qualifying households, but only for windows that improve the EPC rating by at least one band. If your home is connected to the gas grid, HUG2 does not apply.
How to verify an aluminium casement window installer is certified
All installers for government-funded schemes (ECO4, HUG2) must be MCS-certified for windows. You can check the MCS Installer Database at mcscertified.com (MCS, 2026). For non-subsidised installations, look for FENSA (Fenestration Self-Assessment Scheme) or CERTASS registration. These certify compliance with Building Regulations, as confirmed on the GOV.UK page for finding a registered window installer (GOV.UK, 2026).
TrustMark registration is required for any work funded by government schemes. Verify via trustmark.org.uk (TrustMark, 2026). Always confirm certification before paying a deposit.
Aluminium casement windows are a ‘like-for-like’ replacement under permitted development rights
Replacing existing windows with aluminium casements of the same size and design does not require planning permission, as it falls under permitted development. This is stated in the GOV.UK guidance on planning permission for windows (GOV.UK, 2026). If the property is listed or in a conservation area, you must apply for listed building consent or planning permission. Check with your local planning authority before ordering.
Any change in opening direction, size, or style may require planning permission. Always verify with the local council to avoid enforcement action.
Check if your home needs planning permission for window replacement
Frequently Asked Questions
Prices start around £450 per standard 600mm x 1200mm window fitted, according to the Energy Saving Trust's 2026 cost guide. Larger or multi-pane designs cost £650 to £900 per window.
Yes, double-glazed aluminium casements with a thermal break achieve U-values of 1.4 to 1.6 W/m²K, meeting Building Regulations Approved Document L 2025. Triple-glazed versions reach 1.2 to 1.4 W/m²K.
Replacement aluminium casement windows are usually permitted development, but check with your local planning authority. Listed buildings or conservation areas may require consent under UK planning rules.
Double-glazed aluminium casements with thermal break typically have U-values between 1.4 and 1.6 W/m²K. Triple-glazed, argon-filled versions reach 1.2 to 1.4 W/m²K, per MCS 023 standards.
The Great British Insulation Scheme does not cover window replacements. However, the Boiler Upgrade Scheme or ECO4 may support broader energy efficiency improvements, but not windows directly.
