107 CATHEDRAL COMMUNICATIONS THE BUILDING CONSERVATION DIRECTORY 2025 METAL, WOOD & GLASS 3.3 and perimeter seals, can be applied to sash and casement windows without altering their appearance. However, incorrect application of draught strips can lead to operational issues, such as windows becoming too tight to open or poor adhesion causing premature failure. To maintain functionality and aesthetics, conservationgrade draught seals, such as embedded brush seals or compression seals, should be carefully selected and installed with minimal visual impact. For those looking to improve thermal performance further, secondary glazing can be a non-intrusive option. A carefully selected product is an excellent solution for listed buildings where double glazing is not an option as it significantly reduces heat loss while retaining the character of the original windows. Work can be combined with draught-proofing, making it more cost-effective and could address up to 50 per cent of total heat loss. Historic England conducted a study on traditional wooden sliding sash windows, where repairs and draught seals reduced air leakage by 86 per cent, and additional secondary glazing cut it by 96 per cent.1 More advanced glazing solutions include triple glazing and vacuum glazing. Vacuum glazing, in particular, offers the thermal efficiency of triple glazing but with a much slimmer profile, making it possible for retrofitting into historic window frames. Doors are another common source of unwanted draughts. For external doors, installing perimeter draught seals and a brush or rubber threshold seal can reduce air leakage while maintaining the door’s historic appearance. Again incorrect sealing of doors can lead to problems with expansion and contraction in timber, potentially causing warping or operational issues. It is advisable to use flexible materials such as brush seals or discreet rubber seals which will allow the timber to Brush seals and perimeter seals can be applied to sash windows without altering their appearance. To improve thermal performance and reduce down draughts from cold window panes, secondary glazing can be a non-intrusive option. Draught-stripping is a highly effective way of reducing air leakage in a casement window. (All photos this page: Mitchell & Dickinson) 1 www.historicengland.org.uk/research/results/reports/109–2009
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