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What are composite windows?

Composite windows (also known as alu-clad windows) are a small but growing trend when it comes to energy-efficient windows here in the UK. While they may be a lesser-known option here, in Northern Europe composite windows have been a popular choice for decades.

With big Danish brands such as Rationel and Velfac leading the way, what do we need to know about composite windows?

What are composite windows?

What are composite windows made of?

When we think of composite here in the UK we tend to think of a combination of timber and plastic, commonly used for entrance doors. Composite or alu-clad windows are made with a solid wood core and an aluminium outer casing. These alu-clad composite windows are much more sustainable and environmentally friendly than traditional composite because they are plastic-free, and both aluminium and timber are widely recycled.

Forma Plus Triple Glazed
A cross section of a triple glazed alu-clad window

Are composite windows energy efficient?

Absolutely yes! Available in double and triple-glazed units, composite windows can deliver a U-value as low as 0.79 W/m²K. (And when it comes to u-value, low is good!) This is great news for homeowners looking to create a more energy-efficient home, particularly if your plans include lots of glass or large floor-to-ceiling windows.  For comparison, a double-glazed uPVC casement window would have a typical  U-value of around 1.2 W/m²K. 

Can composite windows be used for renovations and older properties?

Yes, there are ranges of composite windows suitable for older properties. There is even a heritage look range (Rationel Forma) which is specifically designed to work with heritage styles and older buildings (Subject to survey and planning regulations) These windows have traditional British style glazing bars and angled glazing beads for an authentic heritage look.

White timber core heritage window
Rationel's Forma range is inspired by traditional timber windows

What about newer properties and extensions?

The Rationel Aura range is perfect for a modern style extension or renovation. The windows in this range have a more modern Scandi-style look and are designed to create maximum light, with slim sightlines and minimalist hardware.

Aura Plus Anthracite Windows
The Rationel Aura range is modern, chic and minimal

What are Velfac windows?

Velfac is the sister company of Velux – the well known roof window manufacturer. Velfac windows are composite or ‘Alu-clad’ windows created for use in new builds or passive house style buildings. Much like Rationel, they offer triple-glazed units and a low U-value of 0.8W/m2K, and as you would expect from a Danish brand the look is beautiful – with a laquered timber internal finish and minimalist scandi style proportions.

Composite Window Velfac V200 Wooden Finish
Velfac windows feature timber on the inside with an aluminium casing on the exterior

How can I find out more about composite windows?

You can get in touch to ask us a question in all of the usual ways or fill out the contact form below to book a consultation in the Norfolk and Suffolk area.

You can also download a brochure below or visit our product pages for further information. 

Book a free quote with us for Composite Windows

Once we receive your enquiry, we’ll contact you to discuss and further understand your project. Typically, we then arrange a complementary site visit, however, in some cases we can provide remote services.


Or, you can contact us!


Either give us a call: 01603 905080
or email:

Get a free quote with us now.

Contact us to discuss your project.

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