Composite timber/aluminium products are being imported into the UK in ever increasing quantities to meet the demand for ‘high insulation’ and ‘sustainable’ window solutions, but are imports really sustainable and the most economic solution for the UK’s construction requirements? Look to place an order today from a reputable European manufacturer and you can be quoted a 16-week plus lead time, and whilst this is just acceptable for new commercial projects it can be a nonstarter for the refurbishment sector.

The transportation of readymade frames takes up much more space than window material in component form, so a readymade product starts to embody more energy and consequently more carbon prior to arrival in the UK. There are a few UK manufacturers of composite windows, all of which are experiencing good order books and with improved lead times to UK contractors over their European counterparts, their future seems to be set. So the time is perfect to look more seriously into how fabricators can become part of this ‘composite revolution’, but until now there have been serious barriers to competition.

Following several campaigns by the timber producers, specifiers are now seeing the benefits of using high performance engineered timber profiles which can be coated to withstand up to ten years weathering without the need for recoating. Add a powder coated or anodised aluminium profile to the outside of the product, and designed correctly, the same timber window will last in excess of 30 years. As timber is a good insulator and sourced from sustainable forests, the timber/aluminium combination is attracting many specifiers in the public sector wishing to specify a sustainable product which is easy to deconstruct and offer 100% recyclability at some point in the future.

Consultants have stated that timber/aluminium composites are the lowest cost option when a 40 year life cycle analysis is undertaken against other materials and combinations.

There are basically two forms of timber/aluminium composites, a timber window with an external cladding of aluminium and an aluminium window internally clad with timber. The latter uses normal aluminium machinery to manufacture and can be noninsulated or is often insulated with polyamide. The internal surface of the product is then clad with timber which is fixed into place with ‘toggle’ type fixings to allow for the differential expansion between the two materials. This method of construction design offers a product which is more expensive than a typical high-performance aluminium window, but does offer very slim sight lines. The high cost usually excludes fabricators on competitive tenders.

The former method, a timber structured window with extruded aluminium profiles added externally, fixed on ‘toggle’ fixings to allow for the differential expansion, is the more competitive option. The downside is that until now the fabricator would need to purchase a large woodworking machine, often
well into a six figure sum, plus dedicated machining cutters and a proprietary timber finishing system.
So whilst a more competitive product can be made, it requires heavy investment and high throughput and the steep learning curve of adopting timber as a main structural framing material.

So whilst the aluminium framed composite is uncompetitive and the timber framed composite requires a heavy investment and steep learning curve, a barrier to entry exists for the fabricator which has ensured, until now, that our European cousins, who have invested heavily in production machinery and
techniques, continue to supply the UK market.

Fortunately there is now a third method of construction which takes the best points from both previous designs of making composite windows and combines these to offer local fabrication and shorter lead times whilst maintaining competitiveness.

Enter the Senior Hybrid System, simple ideas are often the best and it surprising until now that this type
of system has not been available. Simply provide finished timber profiles in ‘bar’ length, mitre and make up frames using a proprietary jointing method. With a minimal investment in a timber mitre saw and a simple router, frames can easily be made up in an aluminium fabrication shop and then re-enter the normal production process to have the aluminium external profiles added and then be bench glazed if required.

By offering shorter lead times from stock profile, utilising existing investment in machinery and workforce experience, can in turn result in better margins being obtained compared to a similar ‘bought-in’ composite product. Importantly, using this method of construction, windows can now be made from the results of a site measure, something not possible before due to extended lead times.

Lennart Jonsson is managing director of Senior Aluminium Systems