In-Situ analysis of traditional sash windows and their heat loss reduction measures

Traditional sash windows often underperform thermally and remain a major challenge for improving the energy efficiency of traditional buildings. Window coverings such as curtains, blinds and shutters have long been recognised for their potential to reduce radiant heat loss, yet they remain underutilised in contemporary practice. Laboratory- and simulation-based studies under controlled conditions predominantly inform the current literature on sash window thermal performance. These often fail to reflect the complexities and variability encountered in occupied buildings. This study evaluates the thermal performance of sash windows in occupied buildings, comparing two categories of interventions: traditional low-impact strategies (shutters, curtains, and blinds) and modern medium-impact solutions (slim-profile double glazing and secondary glazing). The research conducted in-situ U-value measurements on 14 sash windows across five user-occupied traditional buildings in Dublin, Ireland, over 200 + testing days. Test results showed a significant reduction in effective U-values using traditional strategies, which is on a par with efficiency gains from secondary glazing. Traditional measures offer viable nighttime solutions for reducing heat loss through traditional sash windows up to 42% without compromising the traditional building fabric and additional embodied carbon for retrofit. The synergistic effect of traditional and modern measures offers up to an 80% reduction in effective U-value, surpassing any standalone modern measure. The significance of this study is in positioning traditional low-impact strategies as ‘sufficiency’ measures in the context of an apparent conflict between architecture conservation and building decarbonisation.