In the present study, experimental and numerical studies are conducted to identify and improve the thermal properties of the most commonly used hollow concrete blocks in Morocco. The experimental approach consists of characterizing the thermal conductivity and thermal capacity of the basic materials using the guarded hot plate and the differential calorimeter, respectively. The obtained properties have been exploited as input data in the numerical approach to investigate the coupled heat transfer through the concrete blocks using the approximation calculation method suggested by EN ISO 6946, and the three-dimensional numerical simulations using the commercial software ansys fluent. The obtained results showed that the average differences between the 1D and 3D calculations are less than 7.5% concerning the five different studies. In addition, the increase in the width and the number of cavities leads to gain a significant decrease in heat loss and an increase in thermal resistance. For block B4 improvement, the cavities with the previously characterized insulation have been partially filled. The proposed technique ensure high thermal performance by reducing the heat flow at 32%, which increased the thermal resistance of the block by 40.5%.