By Andrew Madge, CEO of Gowercroft Joinery.
Finding a suitable replacement for old and dilapidated, single-glazed windows in listed and listed buildings can be challenging, especially when trying to combine the needs of building protection with the modern desire for a comfortable and energy-efficient living environment.
If the original wooden window frames are too rotten to be repaired, the traditional approach has been to specify handmade, single-glazed wooden replacement parts, which usually means that a relatively poor level of thermal and acoustic performance has to be accepted or chosen to compensate for secondary glazing solutions ,
In an ideal world, most of today’s owners of old and old buildings want to benefit from modern performance standards such as durability, sustainability and a good level of energy efficiency in order to create a pleasant living environment without compromising the original aesthetics.
Energy efficient double glazing
Although superior energy efficiency can be achieved with standard factory-installed double glazing (usually with an argon-filled cavity of 16 to 20 mm), the double reflection of the glazing and the thicker profiles required to accommodate heavy double glazing units are almost the same without exception unacceptable for period properties.
This has led to the popularity of the slim, low line of sight double glazing, which aims to combine some of the features of a slim window with better thermal performance. This is achieved by using a heavier inert gas such as krypton or xenon to reduce the thermal conductivity sufficiently to create a more effective smaller cavity between the panes. The line of sight (which represents the area from the edge of the glass to the top of the spacer bar) is usually reduced to only 5 to 6 mm to allow thinner window sections.
However, this type of window has become controversial, not least within the Glass and Glazing Federation (GGF), since less sealant and desiccant have to be used to achieve such a thin thin layer. This can lead to instability and increase the likelihood of a device failure. In fact, it is currently being discussed whether some of these units actually comply with the Construction Products Regulations (CPR). 1
As a result of these unresolved questions, finding the right balance between performance and aesthetics has become even more complicated and challenging.
An alternative option that is now attracting cultural heritage interest is vacuum glazing, in which all air is extracted to create a vacuum cavity between a low-emissivity glass sheet and a clear float glass sheet. No heat can be transferred without air or gas between the panes, making the energy efficiency much higher. The same applies to acoustic performance
Originally developed in Japan over twenty years ago as a lightweight, energy efficient solution for buildings in earthquake areas in Pilkington Spacia ™ is the first commercially available vacuum glazing in the UK to offer U-values of 1.1 W / m2K on its standard units and 0.9W / m2K on its higher performance Spacia ™ Cool units.
With a total thickness of 6.2 mm (the vacuum cavity is only 0.2 mm), this corresponds to approximately a quarter of the thickness of a conventional double glazing and half the thickness of a typical slim double glazing. It’s also about two-thirds of the weight, making it narrow and light enough to fit in most existing wooden frames without causing any noticeable double reflection.
Vacuum glazing technology now allows owners of historic buildings to replace the glazing of old windows while maintaining as much of the original joinery as possible. It is also used by specialized carpentry companies who want to manufacture traditional looking windows with modern performance advantages for those periods when the original frames cannot be recovered.
A complete window solution
Gowercroft is the first window and door manufacturer to incorporate Pilkington Spacia™ Vacuum glazing technology in a traditionally manufactured heritage range of wooden windows to reproduce the classic look of past single glazed windows.
While the new Heritage range is traditional through and through, it is made from AccoyaÒ, a modern, sustainable wood (the cell structure of which has been treated to increase durability, stability and longevity) and is guaranteed to be sprayed with a unique formulation of protective paint 10 Deliver maintenance-free for years.
Instead of using old-fashioned putty to secure the glass panes like the windows of the past, a traditional putty line is reproduced in the outer profile, which significantly improves the safety and longevity of the coating. Likewise, all modern seals that are supposed to make the windows weatherproof are neatly hidden in the carpentry and only traditional hardware is used.
With its unique combination of contemporary features and modern performance advantages, the Heritage range has been installed in listed properties across the country, including the impressive restoration of the listed Templeton House, Winston Churchill’s former home in Roehampton, which recently won Gowercroft’s award for the British in 2019 Woodworking Association (BWF) for design, innovation and carpentry.
The best of all worlds
Any attempt to find an acceptable, modern solution for a listed property inevitably involves compromise. However, nature conservation officers, planners and owners of listed properties now have this highly functional, future-proof and genuinely personable modern product that is supposed to offer the “best of all worlds”.
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