All you need to know about composite windows
A composite window combines two or more different materials into a single frame, so the finished window performs better than any one of those materials could alone. In practice, that almost always means a warm, insulating core protected by a tough, weatherproof outer skin. The most capable composite on the market is the alu-clad timber window: an engineered timber frame with a powder-coated aluminium exterior, giving you the insulation and character of wood with the durability and low maintenance of aluminium.
What are composite windows?
A composite material is made from two or more constituent materials that have different physical or chemical properties. The combination delivers properties superior to the individual elements. Reinforced concrete is an everyday example. A composite window applies the same principle to fenestration.
There are currently two main types of composite window on the market. One uses an aluminium-clad timber frame, the other an aluminium-clad uPVC frame. Alu-clad timber windows are made largely of timber, while alu-clad uPVC windows are mostly uPVC. Both are overlaid externally with a powder-coated aluminium profile, which creates a more durable, longer-lasting product that needs almost no maintenance and opens up a dual-colour finish for design freedom inside and out.
Alu-clad timber or alu-clad uPVC?
Both are composites, but the core material makes a decisive difference to performance, strength and sustainability. The table below sets the two side by side.
| Feature | Alu-clad timber | Alu-clad uPVC |
|---|---|---|
| Core material | Engineered timber | uPVC |
| Thermal performance | Excellent, low-conductivity timber | Good |
| Strength & large spans | High, supports larger units | Lower |
| Typical lifespan | 40 to 50+ years | ~20 years |
| Embodied carbon | Lower thanks to timber core | Higher |
| Up-front cost | Higher, stronger lifetime value | Lower |
Lifespans are typical industry ranges and depend on product quality and upkeep. Relative embodied-carbon figures for uPVC and wood frames follow published cradle-to-gate research (see references).
Why we choose alu-clad timber
We are committed to windows and doors that are energy-efficient, durable and beautiful, so our composites use aluminium-clad timber frames rather than uPVC. Timber earns its place for three reasons.
Aesthetics and design. Our engineered timber frames are custom-made rather than mass-produced, come in a range of profiles, and are stronger than uPVC. That extra strength bears more weight and allows larger, more impressive units than uPVC can support.
Sustainability and performance. Wood has low thermal conductivity, which makes the timber core an excellent insulator. Our best alu-clad products deliver better U-values than uPVC windows, and timber is a more environmentally friendly material to work with.
Lifecycle and cost. Up front, alu-clad timber usually costs more than alu-clad uPVC. But once you weigh lifecycle and thermal performance, the long-term benefits of timber, lower heating bills and a longer lifespan, outweigh the initial saving of uPVC. Timber frames also tend to add more to a property's value than uPVC.
Our highest-performing triple-glazed alu-clad composites achieve a whole-window U-value of 0.64 W/m²K, with verified PHPP data. That is comfortably inside the Passive House threshold of 0.80 W/m²K, so several models suit Passive House, retrofit and low-energy projects. Download our PHPP data →
The benefits of composite windows
Compared with all-aluminium, all-timber and uPVC windows, a well-made composite offers the best of each without their individual drawbacks.
The alu-clad timber frame is more thermally efficient than all-aluminium or uPVC. Its powder-coated exterior has near-zero maintenance needs, where all-timber windows demand regular painting and treatment, and even uPVC needs more upkeep. The lifespan comfortably exceeds most competing products, and across production, in-use performance and disposal, the timber composite is the more sustainable choice. In short, the blend of materials delivers hybrid properties superior to all-aluminium, all-timber, all-uPVC and even uPVC-cored alu-clad windows.
Our timber composite range. Natural warmth meets modern performance.
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Your questions answered
Have a question? You're not alone. We've answered the most common queries about composite windows below.
What are composite windows?
Composite windows combine two or more different materials so the finished frame delivers hybrid properties that are better than any single material. The two main types on the market are aluminium-clad timber windows and aluminium-clad uPVC windows.
Alu-clad timber or alu-clad uPVC?
We recommend timber composites for their advantages over uPVC: the strength and durability of engineered timber, better insulation and U-values, a longer lifespan and a greater uplift to property value.
Are composite windows better than uPVC?
Timber composite windows generally exceed uPVC in thermal performance, last far longer and carry a lower carbon footprint. Energy savings over that longer life make them more cost-effective in the long run, even though uPVC is cheaper to buy.
Are composite windows worth it?
They usually cost more than uPVC, but they offer a wider range of benefits: better thermal performance, greater aesthetic appeal, a longer lifespan, more environmentally friendly materials and lower maintenance. For a well-insulated home, they are the smarter long-term choice.
How long do composite windows last?
With proper care, quality alu-clad timber composites routinely last 40 years or more, and often 50-plus. That is a considerable uplift on the roughly 20-year lifespan of a typical uPVC window.
Can composite windows be painted?
Yes. Our aluminium-clad timber composites can be powder-coated in any RAL colour, and a dual-colour finish (different colours inside and out) is available as standard. The internal timber can also be repainted later if your scheme changes.
Are composite windows good for Passive House projects?
Who sells composite windows?
Norrsken supply and install beautiful, durable and energy-efficient composite windows and doors for domestic and commercial projects across the UK, including double and triple-glazed alu-clad timber ranges.
Choosing Norrsken
Choosing Norrsken is not just about windows and doors, it is about choosing a partner for your building journey. We supply and install the double and triple-glazed alu-clad timber windows and doors for considered self build and commercial projects. Our focus on exceptional craftsmanship, meticulous detail and customer service runs from first consultation to after-sales support.
Explore our range of alu-clad timber composite windows and doors, and discover the Norrsken difference. If you would like to weigh composites against a single material, our guide to the value of alu-clad timber windows goes deeper on performance and lifetime cost.
Every project begins with a conversation. Share a few details and our team will help you specify the right windows and prepare your quote.
References & further reading
- Salazar & Sowlati, Carbon Footprint versus Performance of Aluminium, Plastic and Wood Window Frames from Cradle to Gate – comparative thermal-performance and embodied-carbon research. Research summary on ResearchGate.
- Norrsken – PHPP 10 modelled U-value data for the Norrsken window range. Download PHPP data.
- Norrsken – The lowdown on U-values and The value of alu-clad timber windows.
- Norrsken – The Passive House Standard – the Passive House standard and window component criteria, via the Passivhaus Trust & International Passive House Association.
