The secondary glazing treatment of large gothic arches in a Grade II Listed University Library

Going with the flow on these gargantuan gothic arches

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Treat Of The Month

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arches shapes and curves

You think you have seen just about every size, shape and style of window – nothing is too difficult to treat…. And then you get to site and are confronted with these towering windows; over 4.5m tall x 1.6m wide, stone reveals, beautiful detailing, and tracery – as well as a Grade II Listing. View of the untreated gothic arched windows in a univerity library, which required acoustic insulation and thermal enhancements Initial reasons for secondary glazing in this library were discussed with the client; acoustic insulation was priority and the secondary benefit of raising thermal efficiency, but they didn’t want an ugly and overbearing treatment. Standing back and doing a quick initial assessment of the windows, configurations began to spring to mind – some aesthetically pleasing, yet some could deem impractical due to access. Starting with a reminder of the factors which would affect the approach to the treatment:
  • Sheer size of the openings – manual handling
  • Weight considerations of units stacked on top of each other and manual handing
  • Access to the location – are there any limiting factors on the maximum size units can be
  • Full functioning of the units and desired benefit achievable
  • Access for installation – is scaffolding required – working at height
The scaffolding build up to ensure a safe installation of Selectaglaze secondary glazing for these large gothic arched stained glass windows Due to the irregularity of the splayed reveals, it was decided for the timber subframe to be manufactured and installed first, then the openings measured for the secondary glazing manufacturing plans. To try and create as unobtrusive treatment as possible, using the flow of the original break lines and sightlines; the treatment was broken up into seven constituent parts and replicated for each of the arched openings: A diagram showing the build up of the secondary glazed units to complete the treatment of the 3 imposing gothic arched primary windows Taking advantage of the deep reveal and potential for a large cavity, lightweight products could be used, glazed with 6.8mm glass to not only achieve the desired acoustic reduction and thermal upgrades but also create a visually pleasing result. Section A – forming the base of the arch, was a Series 10 slimline horizontal slider, providing full access to the stained glass windows for cleaning and maintenance. This window alone weighs 45kg Section B –the series 42 heavy duty fixed lights were used to protect the stone relief - no access was required for cleaning and maintenance of this area. These were 8kg each and formed a solid platform for the build up of further units to the apex of the gothic arch  Section C – a slightly smaller Series 10 slimline horizontal sliding unit was installed, again providing full access to the primary windows. This weighed 27kg, which feels a lot heavier when it is being moved into place and installed at height To follow and accentuate the ornate tracery at the top of the arch the following units were used: Sections D – two Series 42 curved fixed lights. Access to the primary windows could be gained behind the opening, however if maintenance was to be carried out the units could be removed by us Section E – a reverse curved Series 42 fixed light, following the original lines of the stone reveal In an ideal world, the fewer units used to create a treatment the better, however in this case, step by step was best to ensure a safe and beneficial secondary glazed treatment. Scaffolding was erected and added to for each stage of the build-up, ensuring a safe installation. The benefits can already be felt, with a much quieter space and a warmer environment to study in. The black frames of the secondary units and painted timber sub-frame accentuates the imposing gothic architecture, yet blends seamlessly, appearing as if it was always there and part of the initial design.