In-Situ Versus Calculated U-Values of Traditional Solid Masonry and Early Mass Concrete Walls in Ireland: Results from the FabTrads Project

This paper examines the results of in-situ U-value measurements across 36 traditional uninsulated solid walls and early mass concrete construction in Ireland. As the retrofit of poorly performing buildings becomes increasingly important, establishing an accurate thermal performance baseline for common solid wall types is essential. Existing assumptions in Ireland are based on default U-values used for Energy Performance Certificates or on calculated values derived using BR443 or ISO 6946 with reference thermal conductivities, while no large-scale dataset of in-situ U-values for Irish solid wall construction currently exists. This paper introduces a new dataset for such walls and compares it to the associated default and calculated U-values. Brick walls < 325 mm performed on average 36.8% better than default assumptions, while brick walls ≥ 325 mm aligned on average reasonably well with the defaults. However, the results ranged from −18.7 to +33.1% of the defaults. Stone walls performed on average 7.2% better than the defaults but with substantial variability at −54.8 to +40.8%. In contrast, mass concrete walls performed significantly worse than assumed (+37.2%), while an earthen wall exceeded expectations by 21.5%. The findings demonstrate that in-situ U-value measurements provide a valuable, non-invasive means of improving the accuracy of thermal performance assessments for traditional solid walls.