The invention refers to precast blocks for constructions from which modular elements of insulating material, with optimized geometry are obtained, to a network of channels obtained by assembling the modular elements, to a supporting structure, to a process of obtaining a construction by assembling the modular elements. The precast block for construction, according to the invention, comprises an exterior face provided with recessed areas and protrusions such that the thickness g of the precast block wall is uniform, and fastening areas for veneering elements, considering of ribs set on the protrusions, and/or a surface without recesses and protrusions, obtaining a higher thickness of the precast block wall, for the precast blocks destined to be positioned in the areas where the outer surface of a construction obtained from precast blocks is larger than its inner surface thereof, such that the rate of heat transfer of the construction to be uniform on the entire built surface of said construction, for preventing the occurrence of thermal bridges.