This article explains the adjustment procedure of a calibrated hot-box unit and the execution of the corresponding tests to measure the dynamic thermal properties of walls needed to calculate the thermal load of buildings. The results of a test for a heterogeneous wall are also presented, in a dynamic temperature rating. These results are compared with those obtained from a simulation carried out on the performance of the same wall through the application of a finite volume software. Subsequently, the error introduced by assuming one-dimensional heat flow through a nonhomogeneous wall is discussed. This is equivalent to considering the heterogeneous layer of the wall as an equivalent homogeneous layer, which is done in several whole building simulation programs. It is concluded that the error committed may be appreciable, even when the heterogeneities are not excessive. (C) 2008 Elsevier B.V. All rights reserved.