Double glazed aluminium windows are window units that combine two panes of glass with a thermal break aluminium frame, offering low maintenance with improved energy efficiency compared to single glazing. The Energy Saving Trust states that switching from single to double glazing in a typical semi-detached house can save around £195 per year on heating bills (Energy Saving Trust, 2026).
The core of what sets double glazed aluminium windows apart is the thermal break, a plastic or resin strip inserted between the inner and outer aluminium sections. This barrier reduces heat transfer through the frame, addressing aluminium’s naturally high conductivity. Without a thermal break, aluminium windows perform poorly; with one, they can achieve whole-window U-values as low as 1.4 W/m²K, comparable to uPVC or timber. These windows suit modern and commercial-style homes, but the frame’s slim sightlines mean less glazed area than uPVC, which can reduce solar gain slightly.
Construction and how it works
Each double glazed aluminium window contains two panes of glass separated by a spacer bar filled with a desiccant, creating a sealed air or argon gas gap. The gap is typically 12mm to 20mm wide, with argon filling improving insulation by about 30% over air. The aluminium frame is powder-coated or anodised for durability, resisting corrosion and fading. The thermal break, usually polyamide or polyurethane, bridges the frame’s inner and outer sections, stopping cold bridging. The Building Regulations require replacement windows to meet a minimum whole-window U-value of 1.6 W/m²K for new builds (GOV.UK, 2026). Most aluminium systems exceed this.
Energy efficiency and U-values
A typical double glazed aluminium window achieves a whole-window U-value between 1.2 and 1.6 W/m²K, depending on the glass specification and frame design. Low-emissivity (low-E) glass coatings reflect heat back into the room, improving performance further. The Energy Saving Trust notes that double glazing can reduce heat loss through windows by up to 50% compared to single glazing (Energy Saving Trust, 2026). For homes with large glazed areas, aluminium frames offer structural strength for bigger panes without sagging, but the thermal break is critical, frames without it can lose 30% more heat than uPVC equivalents.
Cost and lifespan compared to alternatives
Double glazed aluminium windows cost between £400 and £800 per window installed, roughly 20-40% more than uPVC but less than timber. The premium reflects the material’s strength, slim profiles, and longer lifespan, aluminium frames typically last 30-45 years with minimal maintenance, compared to 20-30 years for uPVC. The FENSA certification scheme ensures installations meet Building Regulations, and all new windows should be installed by a FENSA-registered or Competent Person Scheme member (FENSA, 2026). While aluminium frames are highly recyclable, they conduct heat more than uPVC if the thermal break is compromised, so check for BRE certification or a clear thermal break guarantee before purchase.
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 saves roughly £195 per year on heating bills, which means the windows pay for themselves in just over 33 years. However, the real benefit is long-term comfort and reduced draughts, with the aluminium frames lasting 40 years or more with minimal maintenance. The Great British Insulation Scheme closed on 31 March 2026. It funded insulation measures only and never covered windows or glazing. Using argon gas fill in the sealed units improves insulation by around 30% compared to standard air-filled double glazing, lowering the whole-window U-value to as low as 1.4 W/m²K.
| Item | Figure |
|---|---|
| Upfront cost after grants | £6,500 |
| Yearly savings | £195 |
| Payback period | 33 years |
| 25-year lifetime savings | £4,875 |
What homeowners often get wrong
Many homeowners believe aluminium windows are always cold and inefficient because of the metal frame. Here are the three most common mistakes people make when considering double glazed aluminium windows.
- Assuming aluminium frames are poorly insulated This is a misconception from older designs. Modern double glazed aluminium windows use a thermal break, a plastic strip between the inner and outer aluminium, which drastically reduces heat loss. Without this break, you risk high energy bills and condensation on the frame.
- Thinking all double glazing performs the same Many homeowners choose the cheapest option without checking the U-value. Double glazed aluminium windows with a 16mm argon-filled gap can achieve U-values as low as 1.4 W/m²K, while poor-quality units may exceed 2.0 W/m²K. The difference can cost you £50 more per year in heating.
- Ignoring the impact on solar gain Aluminium frames have slim sightlines, which means less glass area compared to uPVC. This reduces the amount of free solar heat entering your home in winter. If you live in a north-facing property, you could lose up to 10% of passive heating, increasing your reliance on central heating.
Quick reference
- Double glazed aluminium windows save the average UK semi-detached house around £195 per year on heating bills according to the Energy Saving Trust.
- The thermal break in modern aluminium frames reduces heat transfer by up to 50% compared to older non-thermally broken designs.
- 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).
- A whole-window U-value of 1.4 W/m²K is achievable with argon gas fill and a 16mm cavity, matching good-quality uPVC performance.
- Aluminium frames last 40 years or more with minimal maintenance, but you must check the warranty covers the thermal break to avoid premature failure.
Frequently Asked Questions
Yes, with a thermal break they achieve U-values as low as 1.4 W/m²K, comparable to uPVC. The Energy Saving Trust confirms annual savings of £195 when upgrading from single glazing.
Typically 30 to 45 years with minimal maintenance, as aluminium resists corrosion and powder coating prevents fading. The sealed double glazing unit may need replacing after 15 to 20 years.
Yes, aluminium windows usually cost 20% to 30% more than uPVC, but offer longer lifespan and modern aesthetics. Ofgem notes that energy savings can offset the initial investment over time.
