This work focuses on the study of the effect of barley straws addition on the thermophysical properties of sand concrete intended for the construction of an external wall in arid regions. The work has been basically devoted to the study of the thermal properties of two river-dune sand concretes: one without barley straws (SC-W-BS) and another with barley straws (SC-BS). The effect of barley straws addition, wall thickness, air-gap within the wall, wall orientation as well as the wall surface coating on the time-lag (Phi) and decrement factor (f) of the materials have been discussed. The obtained results show that the addition of barley straws considerably improves the thermophysical properties of sand concrete (thermal conductivity, specific heat and density). In addition, the results obtained by the use of the "EnergyPlus" software and its application for an external wall made of these materials show that, in the case of SC-BS, the thermal insulation is markedly improved compared to the case of SC-W-BS. This thermal insulation is also improved when the thickness of the wall is higher and even a further improvement is possible if both faces of the wall are coated. Moreover, the addition of an air-gap within the wall, further improves its thermophysical behavior and the study of the wall orientation effect confirms the results of literature i.e. the south and east direction. Besides all that, the macro-structure of the studied composite appears relatively homogeneous with good adhesion 'straw-matrix'. (C) 2014 Elsevier B.V. All rights reserved.