EXTERNAL ENVELOPE 67
Rooflights with the authentic touch
Keeret Eden from The Rooflight Company discusses retrofitting rooflights to heritage properties to deliver the latest thermal performance standards while also improving user experience
R
etrofitting describes not only an intention to renovate but also to reduce the energy and carbon emissions produced through a building’s use. Preserving the historical integrity of heritage properties with a retrofitting target requires a more delicate touch than straightforward renovation. Typically, retrofitting uses a ‘fabric-first’ approach that – among a number of other factors – requires an assessment of the balance between thermal efficiency, lighting and ventilation. Fitting new rooflights to old buildings can be appropriate to address these elements, providing that the roof window solution respects the building’s heritage.
Whether the aim is to replace existing rooflights for a higher thermally performing solution or introduce new roof windows to balance light and ventilation, in protected heritage properties maintaining the original design elements of a rooflight is paramount. Preserving history in this way calls for close attention to detail. By carefully studying how manufacturers created the original rooflights, they can be replicated in modern replacements. Features of the original Victorian rooflight include stepped glazing edge that allowed water to drain away without getting trapped by putty at the cill; glazing clips that held the thin sheets of glass in place preventing glazing displacement; top hung with exposed hinges; an integral glazing bar, and slim putty facing that secures the glass in place.
Retaining the finer design detailing in a modern performing unit allows the structural integrity of the building to be preserved, as well as creating an aesthetically seamless transition between old and new.
ADF JULY/AUGUST 2023
Optimising thermal efficiency Optimising thermal efficiency is a delicate balancing act. Modern rooflights use double glazing to achieve an optimum whole window U-value. A true conservation rooflight will maintain the Victorian style stepped edge feature on the glazing unit for authenticity. Equally, as modern manufacturing methods allow for a robust glazing installation, the purpose of retaining glazing clips in 21st century design is to enhance the overall aesthetic character. An instantly recognisable feature of
the Victorian rooflight was the glazing bar. Modern glazing technology has evolved with larger glass panels readily available, meaning rooflights can now be constructed from one uninterrupted panel of glass, allowing for a thermally decoupled glazing bar, and thus vastly improving the thermal performance rating. As a distinctive feature, the glazing bar is still incorporated into modern designs to maintain this key element of authenticity. The combination of double glazing and a thermally decoupled glazing bar support the retrofitting principles.
Silicone facing offers a modern and efficient solution to sealing between the glass pane and the frame, creating weather resistance and optimum energy efficiency. Combined with a slim frame profile, the angled silicone wedge imitates the putty used in older construction methods without adding bulk to the frame. Retrofitting heritage properties with a rooflight that shares this design feature results in not only a thermally performing solution, but also in an aesthetically accurate replica of the original design.
Another key feature of the original
Victorian rooflights was the flush installation with the roofline. A flush finish
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Retaining the finer design detailing in a modern performing unit allows the structural integrity of the building to be preserved and creates an aesthetically seamless transition between old and new
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