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Restoring original features with bespoke secondary glazing

Category:

Treat Of The Month

Tags:

refurbishment and conservation, thermal, energy efficiency, listed building, sustainability

During a retrofit of two Grade II Listed Central London town houses, the thermal properties of the original windows were identified as being inadequate for 21st century comfort. Selectaglaze was approached to devise a secondary glazing treatment which would address these thermal issues. In this treatment, the designer’s brief was to restore the original look and sightlines of the primary glazing. Replacement windows were prohibited due to the building’s Listed status, so the designer approached Selectaglaze to come up with a solution for this issue. Specifying secondary glazing for older properties is both a science and an art. Thought has to be given to how the treatment will function, what benefits are required as well as the visual impact it may have. Older properties can be particularly challenging due the distortions and idiosyncrasies they present. Over time features such as windows can be pushed and pulled out of square by subtle changes in the fabric of the building. These changes are so slow and gradual, that generally all the elements of the window adapt, yet the whole still functions. Treating older windows with secondary glazing can be very challenging when working with these irregularities. These London town houses were built in the early 19th century in a style influenced by both the Georgian and Regency periods. A key feature of these town houses is their large, symmetrical, evenly spaced and aligned sash windows. Over the period of nearly two centuries, the primary windows had become significantly distorted due to the gradual subsidence of the property. None of the windows were true and no one window aligned with any other. The historic reveals were not designed with secondary glazing in mind, very few are. The distortion in the original reveals, although charming, can have a negative impact and draw attention to new additions such a secondary glazing. However, in this refit the architect had a particular opportunity, as all of the walls and reveals were being relined to improve thermal performance. As part of the relining work came the chance to design a reveal specially to accept secondary glazing creating a seamless, elegant result with all the benefits of modern glazing. Sectional detail of the treatment A rebated reveal was created so that the secondary glazing would sit within the rebate giving the impression that it was an integral part of the original design all those years ago.  On the cavity side, the reveal aligned with the staff bead joint and the inside line of the secondary frame. On the room side the reveal was built traditionally providing that all important seamless look. Reveal aligned with staff bead joint The results look amazing, you would be forgiven for not even noticing that secondary glazing is even there. In this way Georgian symmetry was regained and 21st century comfort was added to these irreplaceable buildings.