Why the oldest window frame material is the modern choice

As the industry searches for new alternatives to PVCu, Tony Pell of The Wood Window alliance investigates the resurgence of timber window frames

Architects appreciate the look and feel of high quality materials, but are naturally attracted to innovative ideas, especially when they bring the promised of enhanced performance. So it’s interesting to see timber – the oldest of materials for window frames – enjoying something of a renaissance over the last few years. It’s not something that’s happened by chance, but the result of a determined effort by the industry to shake off earlier performance issues, while at the same time reinforcing its sustainability credentials.

There has been a significant investment in the quality and engineering of wood windows in the UK in recent years.
The days of site-finishing single-glazed redwood frames are long gone.

Now, fully factory-finished double or triple-glazed windows are the norm, made from defect-free, laminated, slow-growth Scandinavian softwood that has a 60-year planned service life (commonly twice as long as PVCu).

The industry has also listened to what architects want. All Wood Window Alliance (WWA) members are BIM-ready and offer Environmental Product Declarations (EPDs), while most can provide Secured by Design certification. Windows that are easier to clean or redecorate from inside a building have been developed, both sliding sash and casement; as well as factory finishing in different colours, inside and out; and new, more durable products using modified wood such as Accoya, or aluminium-clad timber systems.

With the adoption of warm-edge spacers, low-emissivity glass and argon gas fill, double-glazed timber windows are now widely available with U-values of 1.2 W/m2K, while triple-glazed windows can achieve 0.7 or even lower.

Environmental considerations

With the spotlight on low carbon construction and sustainability, timber is enjoying a revival in the construction industry, and the benefits are just as applicable when timber is used for window frames in developments of any size and scale. All members of the WWA offer FSC or PEFC Chain of Custody certification, and the organisation has worked hard to provide the evidence to back up environmental claims being made by window companies.

Tony Pell, chairman of the WWA, commented: “We worked with the British Woodworking Federation to complete a feasibility study for a typical wood window frame against the Materials Health elements of the stringent Cradle to Cradle Certified standard.” The results show that wood is a healthy option that can easily

U-VALUES

Double-glazed timber windows are now widely available with U-values of 1.2 W/m2K meet the Silver level of the standard, making timber a good choice for any eco or conservation project.

This study complemented a Life Cycle Assessment conducted by Heriot-Watt University showing that all timber frame types – engineered softwood, modified softwood and aluminium-clad timber window frames – made to WWA standards are more environmentally-friendly than PVCu in every end of life scenario considered. The same study calculated that a standard wood window would save 160 kg CO2e when fitted instead of a PVCu window, making a potential saving of over 1.5 tonnes of CO2e for the average home from the window frames alone.

About The Wood Window Alliance

Founded and managed by its members, the WWA has more than 20 members manufacturing many different types of timber windows and doors. It provides the reassurance of high quality, performance and sustainability standards. All products are third-party certified to meet British Standards, typically offering unbeatable warranties, and all members are BIM ready, have FSC or PEFC Chain of Custody certification and meet all building regulations including Part Q (Security).

Tony Pell is chairman of The Wood Window Alliance