U-value determination of masonry walls with complex shape units and thermal rendering

Abstract

Single leaf masonry walls with the application of thermal rendering can be an interesting solution for façades, providing the performance of its components can lead to a competitive thermal resistance. The determination of the walls U-value will therefore be of most importance. Practitioners often use reference values available in literature or declared by manufacturers to determine U-values that will be computed in building thermal calculations. The case of masonry walls is typically sensitive in the sense that manufacturers frequently base the declared values on calculations using EN ISO 6946 methodology. For the case of masonry using complex shape units and thermal rendering the definition of the expected U-value raises several problems that have to be tackled so that manufacturers declared values can be trusted.Laboratory tests were conducted in a wall composed of a thermal rendering applied over a single leaf masonry of complex shape units. The objective was the evaluation of the U-value and the validation of calculation methodologies for its calculation. The tests included material properties evaluation and U-value determination of the wall using a climate chamber and fluximeters.Numerical simulations were applied with the focus on the calculation of the thermal resistance of masonry through two approaches. One was made through a simplified 2D model based on EN ISO 6946 calculation methodology, and the other was made through a 3D model based on the finite element method (FEM). The numerical results obtained from the simulations were compared to the experimental results obtained from laboratory tests. The differences observed and the results obtained in the material characterization phase supported a discussion on correction factors that can be used to improve the feasibility of U-value calculations for the studied wall.