The time lag (TL) and decrement factor (DF) are essential for the heat storage capabilities of
building elements, which strictly depend on the thermophysical properties of the elements.
Many investigations are presented in literature arguing to find the influence of each
thermophysical property on TL and DF by keeping the other properties constant. This study
aims to investigate the effect of each property on TL and DF, utilizing relationships between
the measurement values of the thermophysical properties of wall materials. Therefore, first,
132 new concrete wall samples were produced, and their thermophysical properties were
tested. Secondly, TL and DF values for each building element are computed from the solution
of the problem by Complex Finite Fourier Transform (CFFT) technique. Finally, a
multivariate regression analysis has been performed, and the variations of each
thermophysical property versus TL and DF are presented, and also the findings are compared
with literature. The results show that each property alone (keeping the other properties
constant) is not adequate to identify the thermal inertia and thermal performance of a wall
element. Besides, 87.3 % decrease in thermal diffusivity corresponds to 6.03 h increase in the
value of TL and 88.8 % decrease in value of DF; respectively, for W1 wall assembly