Optimising thermal performance in historic solid wall buildings: The role of orientation, natural insulation and building simulation

Purpose – This study examines how façade orientation influences in situ thermal transmission in historic solid wall buildings and evaluates the measured performance of natural insulation materials when applied to traditionally constructed fabric. The aim is to improve the understanding of how orientation and exposure affect retrofit outcomes in hard to treat heritage buildings, supporting more evidence informed retrofit decision making. Design/methodology/approach – Two pre 1910 stone buildings located in coastal Cornwall were monitored using medium duration in situ U value measurements in accordance with ISO 9869 1. Baseline and post retrofit performance was assessed across multiple façade orientations using sheep wool, hemp wool, wood fibre and synthetic polyisocyanurate insulation. Measurements were undertaken over periods ranging from approximately 11–20 days per test, enabling diurnal and exposure related effects to be captured. Measured U values were subsequently used to inform dynamic thermal simulations to explore the sensitivity of energy performance predictions to orientation dependent inputs. Findings – Measured U values varied substantially with façade orientation and insulation material, including differences of up to approximately 16% between opposing elevations under comparable construction conditions. Parallel measurements on the same façade also revealed notable local variability. These results demonstrate that short duration testing and uniform performance assumptions may obscure orientation-related behaviour in historic solid wall construction. Natural insulation materials exhibited thermal performance comparable to polyisocyanurate in several orientations when assessed under real world exposure conditions. Research limitations/implications – The study is limited to two case study buildings within a single climatic region and to the specific wall constructions tested. The findings should therefore be interpreted as indicative rather than generalisable. Further work across a wider range of building typologies, orientations and climatic contexts is required to strengthen transferability. Practical implications – The findings highlight the value of extended in situ measurement when assessing retrofit options for historic buildings and demonstrate that orientation specific performance can materially influence measured outcomes. This supports a more cautious and evidence led approach to retrofit design where material choice and exposure are considered together. Originality/value – Whilst research into the influence of orientation on thermal performance has previously been undertaken, it is rarely quantified through medium duration in situ measurements across multiple insulation materials within the same historic buildings. This study contributes empirical evidence derived from extended real-world monitoring, enabling side by side comparison of natural and synthetic insulation performance under comparable exposure conditions. Highlights – Extended in situ monitoring shows façade orientation can influence measured U-values in historic solid wall buildings. Orientation-related variation of up to approximately 16% was observed under comparable construction conditions. Long-duration ISO 9869 compliant measurements reveal divergence between assumed and measured retrofit performance. Natural insulation materials demonstrated thermal performance comparable to polyisocyanurate in certain orientations when assessed in situ.