The latest research for the Wood Window Alliance (WWA) provides proof that windows manufactured to the group’s standards have a service life of 60 years.

This latest research builds on previous life cycle assessment research by Imperial College for Akzo Nobel in 2004. That research showed that timber windows made to the standards of the Timber Window Accreditation Scheme, which is run by the British Woodworking Federation, gave a 40-year service life. Six years on, the new study by Imperial College used ISO 15686-8:2009 methodology to assess and quantify the impact of the major advances in design, manufacturing and coatings technology incorporated in today’s WWA windows.

And the new service life story does not end there – enhanced maintenance and sheltered conditions can extend that service life to 80 years and even beyond.

Dr Richard Murphy of Imperial College, who undertook the new study, said the research implies that there is no reason why today’s WWA windows should not last a lifetime, in the same way that Victorian and Edwardian wood windows are still to be seen in buildings today.

This latest research validates the huge advance in manufacturing standards over the past five years or so. It can now be said WWA windows will actually last the design life of a building.

The Imperial College data was also used to provide a new whole life costing analysis. The work considered building lives of 60, 80 and 100 years across a range of exposure conditions and maintenance regimes for two WWA A and C energy-rated windows and comparable PVCu windows. As the graph shows, the results proved that the extended life of a WWA window results in lower whole life costs than the PVCu windows at 60 years and beyond, giving cost savings of 2-7%.

All this builds on the first piece of major research announced by the WWA last year. This was the first study to measure the embodied energy of wood empirically and showed that WWA windows are carbon negative. Davis Langdon measured the embodied energy of a selection of WWA standard A and C-rated windows over 30, 60 and 100-year service lives and the results showed that, despite carbon emissions from transport, production, maintenance and end of life, WWA frames are still carbon negative because of the carbon sink effect of sustainably-managed forests.

All WWA windows must be sourced from sustainably-managed forests where new growth exceeds harvest. That means the WWA can legitimately claim that every WWA window specified instead of a PVCu window saves around 89kg of CO₂e over the window’s life. For a typical house, that’s around 0.75 tonne of CO₂e, the equivalent of driving almost 5,000km in a typical family car. To put this in perspective, if just half the PVCu windows fitted in the UK in 2008 had been WWA windows there would have been a saving of over 300,000 tonnes of CO₂e.

Research is the cornerstone of the Wood Window Alliance’s campaign, which was launched three years ago. “The campaign has become the authoritative voice on wood windows, supported by the one thing that influences, informs and drives specifiers and architects – independent research,” said WWA chairman Sean Parnaby. “We will continue to produce reports on the evolution of timber windows that will prove that timber is the longer-lasting and environmentally-friendly option.

Wood Window Alliance criteria

WWA members’ windows:
● meet the minimum standards set out in BS 644, the main British Standard for wood windows, or equivalent standards from other countries;
● meet the performance standards for wind and weather resistance of BS 6375 Part 1;
● meet the minimum performance standards for operational aspects of BS 6375 Part 2, or equivalent
standards from other countries;
● are accredited by an independent UK or European body to prove
compliance with those standards;
● are made using timber that is independently certified as legal and sustainable by a scheme recognised by CPET ie FSC, PEFC, SFI or CSA;
● have chain of custody certification;
● have service life warranties for durability, paint life, ironmongery and insulated glass units;
● meet or better the UK Building Regulations recommendations for energy efficiency.

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