Can the conservation issue be maintained?

The Future of Single Glazing. Can the Conservation Issue Be Maintained?

T R Wakeman, OBE, CEO The Performance Timber Products Group

Timber has rightly regained its superiority in being the only natural and sustainable material for the manufacture of high quality windows and doors.  Recent research identifies that timber is energy efficient and over ifs life cycle could actually outlive the building in which it has been installed.

timber sash windows

This is supported in a recent study of a Lifetime Cost Analysis commissioned by the Wood Window Alliance (WWA) which was carried out by the Heriot Watt University in 2012. It found that timber windows have a life expectancy of 60 years or even more, and is carbon negative. By comparison plastic windows have to be replaced every 35 years or so. This means that although the initial cost of a timber window can be as much as 25% more than a plastic equivalent the total lifetime cost should be the primary consideration.  In this, timber offers the lowest cost option every time. Consequently, modern timber windows are regaining market share in the UK and now represent some 25% of demand by value.


The argument from conservation bodies and owners of period properties come to the fore, in my experience, whenever someone wants to invest in their properties and improve them, as is their right and as custodian of a notably special building.  No one wants to see ugly facades compared to historic design such as Elizabethan, Georgian, Edwardian and Victorian architecture so, from that point of view, design is critical and the fine line, particularly in joinery products such as windows and doors, need to be maintained if replacement products are to be installed in properties of these eras. Timber, because it was used originally, does provide the answer when it comes to maintaining these elegant features, no matter how the engineers try to replicate the joints and glazing bar details provided by the original timber material; the plastic industry fails to meet the criteria.

So, whilst the original prime cost comparison between timber and plastic favours the latter, in the long term timber is more cost effective. This does depend of course on preventative maintenance being carried out in accordance with the manufacturer’s instructions whether for timber or plastic products.

Taking all of the important requirements of this world in which we live: we must reduce carbon emissions, conserve energy and use sustainable products, it doesn’t take rocket science to support the argument for timber. Significant carbon savings can be made over this lifetime when substituting a timber window for that of PVC-U material which equates to roughly 1.5 tonnes of CO₂ per average home. This is the equivalent of driving over 5,000 miles in a small family car.

Single glazed or double glazed

What do we do about the argument from conservationists, who almost always insist on maintaining single glazed products, to protect the integrity of the installation and glazing methods used in the original design and the use of fenestration products? Should we still be using single glazed sash and casements using putty for the fixing? It seems to me that this argument is fast losing its strength as the modern glazing methods using double and even, in some cases, triple glazing is really the only way to go and satisfy the needs of the environmental legislation. Double glazed units of at least 24mm provides for the best thermal and acoustic performance. Modern timber windows produced today allow for the glazing to be applied from the inside so as to protect the integrity from the elements, and also enhances security and aesthetics.

It beggars belief that, from 5 feet away, you couldn’t tell the difference between double glazed timber windows and putty glazed single glazed windows, that conservation officers and planning control object to the modern way of satisfying the real needs of the home owner. At the Listed Property show last year, when our award-winning brand Mumford & Wood exhibited new, high performance and engineered designs built to replicate historic design but using modern glazing techniques, that over 95% of all visitors to our stand - they were all owners of listed properties - wished for double glazed windows. In almost all cases they had refusals from their local planners to install modern double glazed timber windows, with the recommendation, if you can believe it, to install ugly secondary glazing as the only alternative. This last offer was bred in the 60s and 70s along with ghastly plastic windows to create an industry that quickly grew to dominate the replacement window and doors market. Thank goodness this trend has now been reversed and timber is taking its rightful place at the top of the home owners wishes.

Another way of cutting corners on the subject of glazing has been the malpractice of using butchered double glazing spacer bars to reduce the width so as to create a narrow spaced double glazed unit. It has been proven that these untested products almost always fail in integrity in a short space of time. Our trade association, the British Woodworking Federation (BWF), produces regular bulletins on these subjects and offer particularly good advice which is to not specifiy narrow space double glazed units unless they have been fully tested and certificated.

The acid test for any successful design or product application is the acceptability from the consumer to satisfy not only aesthetics but also performance against the elements and to satisfy today’s essential requirement which is to save our planet.  

The Government is committed to building new homes from 2016 that would be zero carbon and the Zero Carbon Hub demonstrates this so the potential for timber based products to create a new generation of low-carbon energy-efficient homes is huge.

The Conservation™ Range of Timber Windows & Doors


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