This paper investigates the impact of moisture content on the thermal inertia parameters of building material layers. Moisture variation affects the energy storage and therefore the energy gains/losses through buildings. To this effect the decrement factor and time lag are determined for three types of concrete layers and one of solid clay-bricks masonry layer. Their consideration is essential to enhance the design of building elements, from a thermal point of view, when exposed to varying moisture content conditions. Moisture content and relative humidity variations of each analysed layer, as defined by specific moisture storage functions, are shown to interrelate non-linearly with the layer resistor-capacitor circuit section parameters (thermal conductivity and volumetric heat capacity) showing notable consequences on the thermal inertia parameters. The dynamic thermal analysis is accomplished by using the thermal-circuit modelling approach and the nodal solution method. The deterioration of decrement factor and time lag due to moisture content are illustrated by appropriate metrics. Computer results for the studied layers with thicknesses varying from 10 cm to 50 cm show the influence of the variation of relative humidity and thickness on the decrement factor and time lag. (C) 2016 Elsevier Ltd. All rights reserved.