In this study, the effects of thermophysical properties and thickness of a wall of a building on time lag and decrement factor have been investigated. For this purpose, one dimensional transient heat conduction equation was solved using Crank-Nicolson scheme under convection boundary conditions. To the outer surface of the wall; periodic boundary conditions were applied. A very general code which can take care of composite walls under any kind of boundary condition was developed. Single and combined effects of the thickness and thermophysical properties on the time lag and decrement factor were investigated. It was found that thermophysical properties have a very profound effect on the time lag and decrement factor. The computations were repeated for different building materials and the results are discussed. (C) 1998 Elsevier Science S.A. All rights reserved.