Thermal conductivity testing of a range of Irish traditional bricks using Transient Line Source methodology

National policy in Ireland is beginning to address the global challenge of retrofitting the existing building stock to reduce heat loss and increase energy efficiency. Any retrofit strategy is reliant on a good understanding of the hygrothermal behaviour of the existing building envelope. The FabTrads project intends to improve BER (DEAP) assessments and support hygrothermal modelling in accordance with IS EN 15026:2007 by measuring the hygrothermal properties of a range of building materials in use in Ireland between 1700 and 1940 through laboratory testing, and by measuring the in-situ U-values of traditional walls. Knowledge of the thermal conductivity of a building material is fundamental to the calculation of U-values of building assemblies. Standardised thermal conductivity testing routines for building materials are generally steady-state methods, which require precise and complex sample preparation in the laboratory. This paper describes how a transient line source method commonly used for determining the thermal conductivities of soil and rock (conforming to ASTM D5334-22) can be adapted for use on traditional bricks in the laboratory and discusses how this simplified testing routine allows for wider availability of testing on inhomogeneous, irregularly shaped and friable samples at different moisture contents. The measured thermal conductivities of ten historical Irish bricks at 50% RH ranged from 0.361 W/mK to 0.948 W/mK. At saturation level, an increase to between 194% and 347% of the original value was observed. The paper considers the relationship of measured thermal conductivity to apparent density and contributes to a better understanding of the suitability of transient line source testing for traditional building materials. It highlights issues with current methods of accounting for the impact of moisture content on the thermal conductivity of a material Thermal conductivity testing; transient line source; historic brick; traditional building materials; National Calculation Methodology; moisture dependent thermal conductivity