What are Composite Windows?

Looking for an energy-efficient, low-maintenance window? Composite frames could fit the bill, says Chris Bates
by Chris Bates
10th February 2013

If you’re looking for a high-performance fenestration solution for your project, composite windows could be the answer.

Available in a wide range of styles and specifications, these factory-made products combine an exterior cladding (usually aluminium) with a timber core. The result is a durable composite window with a low-maintenance finish that still offers the charm of wood internally.

Alu-clad windows: the basics

The fact that composite window frames are easy to maintain has obvious benefits for self-builders and renovators – put simply, they’ll go a long way to reducing the amount of time and money you need to spend re-finishing windows every few years. But the aluminium cladding offers another tempting bonus – its durability makes it a great choice in coastal regions of the UK, where salt spray can be an issue, and other areas exposed to harsh weather conditions.

Using engineered timber (either hardwood or softwood) for the internal framework helps to reduce movement in situ. It also means there’s no need to incorporate a thermal break – which is a necessity for fully metal windows. Timber is a natural insulator, so composite frames are easily capable of meeting high levels of energy efficiency – but do check the wood has been sustainably sourced (look for PEFC or FSC certification).

These windows were initially developed for the chilly climates of Scandinavia and Canada, so they’re designed to minimise heat loss and many ranges offer both double and triple glazing as standard options. Many triple-glazed versions are specifically sold as being suitable for achieving Passivhaus standards (where the whole window U-value must be 0.8 W/m2K or better, as opposed to the much less efficient 2.0 W/m2K required by Building Regulations in new build scenarios).

Composite windows are supplied pre-assembled, so they’re fully-glazed and factory-finished when they arrive on site for speedy installation. High-quality units are built to last – Crittall suggests a life cycle of over 40 years for its range, for example. That’s comparable to conventional timber windows, and easily beats the widely-recognised 25-35 year lifespan of PVCu units.

Styles & finishes

When it comes to achieving a modern look, composite windows are a fantastic choice. The sleek lines of the powder-coated aluminium cladding are the perfect complement to a contemporary setting – although traditionally-styled versions are starting to come onto the market. In many cases, matching external and bi-folding doors are also available.

Most manufacturers offer a RAL colour matching service, so you can run the whole gamut of frame tints. A bold choice might make your windows stand out as a key feature of the facade, for example, or you could pick a more muted shade that allows the frames to blend in with the building. Gloss, matt and satin powder-coated finishes are all available, while some manufacturers offer anodised aluminium, too.

Internally, the engineered timber can be lacquered, stained or painted to suit your tastes. Retaining a wood finish can bring natural warmth to your decor, while painting gives you the opportunity to either highlight the windows’ sleek profiles or match your wall finish for a clean look.

The majority of opening formats are catered for in the composite market, including: flush and stormproof casements; reversible types that tilt 180° to offer easy access for cleaning; and the popular European-style ‘tilt-and-turn’ models.

Sliding sash windows with composite frames are less common at present, though they are available through companies such as Sash Window Aid. Be aware, however, that their clean lines can rule them out for heritage projects – they’re more likely to be acceptable on new builds.

What do composite windows cost?

Considering they’re basically timber windows with an additional weatherproof cladding, it’s no surprise that composites occupy the upper end of the pricing spectrum.

Expect to pay from around £350 per m2 for standard casements, and significantly more for ultra-efficient triple-glazed versions.

But remember these windows are aimed at homeowners looking to achieve a high spec, low-maintenance build with good energy efficiency and low running costs. So you’ll reap plenty of benefits in the long run, especially if you’re building near the coast.

Photo: Composite windows from Kloeber

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