The evaluation of the effectiveness of the use of non-removable void formers in monolithic reinforced concrete slabs is based on the analysis of the results of numerical modeling of four series of samples with different dimensions in plan and the main working reinforcement. A comparative analysis of the values of compressive stresses in concrete and reinforcement, as well as tensile stresses in reinforcement for reference samples (full-bodied) and samples with non-removable void generators of the Sibform system was performed. According to the results of the study, it was revealed that the use of non-removable void formers in a monolithic reinforced concrete slab does not affect its strength, but it allows to reduce the consumption of concrete and, as a result, the weight of the structure by an average of 20%.