Despite being a material used over time, soil has lost its space as a building material with the appearance of the most diverse materials and techniques that today are considered traditional. However, with the latest environmental and energetic concerns, earth construction techniques appear revitalized. Recently, the Interlocking Compressed Earth Block (ICEBs) masonry system has experienced considerable development. Some studies prove the potential of new stabilization techniques, such as alkaline activation, to improve the mechanical performance and the durability of the blocks, allowing the incorporation of industrial by- products. The high energy consumption for buildings acclimatization has been another aspect of high discussion. Many times, buildings constructed with earth are referred as an example with respect to the thermal performance. In this sense, an assessment of the heat transfer coefficient of the ICEBs was carried out. The results show that the ICEBs system performs poorly when compared to other current construction materials regarding the heat transfer coefficient, but presents an improvement when stabilization is done with alkali activated fly ash compared to other earth based materials.