The U-value of a dried wall made of vertically perforated porous clay bricks is determined by means of three different methods stated in EN 1745. These are the calibrated hot box measurement according to EN ISO 8990 and two numerical methods using for the thermal conductivity of the porous clay either a measured value or a tabulated value based on density. The results of these methods are compared and discussed leading to a proposal for the refinement of the model chosen for the numerical analysis. (C) 2002 Elsevier Science B.V. All rights reserved.