By Kevin Underwood, BWF Technical Director
In June 2019, Parliament passed legislation requiring the Government to reduce the UK’s net emissions of greenhouse gases by 100% relative to 1990 levels by 2050. Doing so would make the UK a ‘net zero’ emitter. Achieving net zero requires a balance between reducing existing emissions and actively removing greenhouse gases from the atmosphere.
It is estimated that the built environment is responsible for around 40% of global carbon emissions, so a focus has been rightly placed upon the construction industry to look at utilising lower carbon materials. It is widely accepted that timber, as a core building material, can support the UK build a zero-carbon future. However timber is still being overlooked when it comes to the specification of windows despite the Government calling upon the UK to ‘build back better, build back greener’. Via the Wood Window Alliance (WWA), A BWF owned and managed scheme, I get general feedback from the market that the end-user can sometimes perceive wood windows to not be as durable as PVCu alternatives, or that the cost is slightly higher.
In this article I provide evidence to prove that such perceptions are outdated and highlight how the environmental credentials of both new and existing (i.e. retrofit) buildings when wood window frames are specified.
Independent Insight into Wood Windows
The WWA have commissioned a number of studies on the environmental credentials of wood window frames to help understand how they compare with other materials.
A ground-breaking study for wood windows was ‘Whole Life Analysis of Timber, Modified Timber and Aluminium-Clad Timber Windows’ by Heriot Watt University. Published in 2013 this study compares the service life, ownership cost and environmental impact of windows across four different frame materials. More than anything, this study shows that wood window frames (made to the WWA specification) can outperform PVCu equivalents by almost 30 years and consequently have the lowest whole life costs and the lowest environmental impact.
Wood Windows for Longer Life and Lower Environmental Impact
The Heriot Watt study found that in moderate UK climate conditions, a typical wood casement window frame (made to the WWA specification) has an expected service life between 56 and 65 years. This is almost double that of a PVCu equivalent which in the same conditions has an expected service life of 26 to 35 years.
Over this expected service life (which averages at 60 years), the wood window frame was found to offer the lowest cost alternative too. Whilst PVCu manufacturers claim that there windows are ‘maintenance’ free, we would argue that no window can be as they still require cleaning and attention given to the hardware (hinges and handles). Where wood window frames especially differ from PVCu equivalents is that they can easily be repaired if damaged and also when the colour begins to fade, they can be easily repainted. Planned maintenance prolongs the life of the wood window frame and its carbon store effect, reducing the impacts caused by new replacements.
The Heriot Watt study found that a typical wood casement window frame (made to WWA specification) is carbon negative over its lifecycle. As part of membership criteria, all WWA manufacturing members must hold either FSC® or PEFC™ chain of custody. Timber sourced from sustainable forests not only means that more trees get planted than chopped down, but it’s a proven way to reduce carbon dioxide in the atmosphere. Wood products are carbon stores and growing forests are carbon sinks.
Creating a better understanding of use of wood windows
It’s important that architects and specifiers working on both domestic and commercial buildings keep up to date with the evolution of timber products and avoid common misconceptions about wood. Correctly specified timber products are crucial to helping move the construction industry towards building more sustainable buildings that create the optimum environment for occupants, and capitalise on timber’s inherent properties as a construction material.
To help with continued learning the WWA have invested in an Interactive Wood Window and Door CPDi. The educational programme is broken down into bitesize chunks based on key themes, and each session can be taken alone, or as part of the wider series.
Four modules are currently available to access free of charge, these explore:
- the circular economy;
- the benefits of timber school buildings;
- building nature into architecture; and
- the natural evolution of the wooden window.
Providing practical guidance and support with specification, the modules offer a comprehensive overview of how high performance, quality buildings can be created with the use of timber products, with a specific focus on windows and doors.
To access the Wood Window and Door CPDi visit https://cpdi.bwf.org.uk/