The article is devoted to particularly important contemporary problems, namely usage of energy-saving and ecological materials in load-bearing structures of buildings. This issue is discussed in the paper in respect of floor slabs. We propose to combine traditional materials (concrete and steel reinforcement) with energy- -efficient material (non-autoclaved foamed concrete) in floor slabs structure. It is assumed that employment of precast-monolithic reinforced concrete floor slab with usage of non-autoclaved foamed concrete can afford to decrease dead weight of floor and foundation loading, and to guarantee good thermal and acoustic insulation between storeys.