The presentation will summarize and discuss values of field measured normalized impact sound pressure level L’n,w measured sideways with different configurations of concrete slabs on ground within buildings. All results are adjusted to receiving room volume of 100 m3 and with thickness of concrete slab 80-100 mm. Measurement on continuous concrete slab on expanded polystyrene gives L’n,w between adjoining rooms of 74 dB. Different principles of splitting have been investigated to evaluate the effect on L’n,w. The configuration where only the concrete slab is split (and with a plastic film between the concrete base and the upper layer of expanded polystyrene), gives L’n,w of approximately 66 dB which is 8 dB lower than for a continuous bare concrete slab. When both the concrete slab and the upper layer of expanded polystyrene are split, measurements show L’n,w of 58-61 dB for the case of no flooring, which is 13-16 dB lower than for a continuous concrete slab (no split). When both concrete slab and all layers of polystyrene are split down to continuous foundation measurements show L’n,w of 55 dB. The situation with concrete slab and all layers of polystyrene split and with no foundation beneath gives L’n,w of 46 dB. Consequences for airborne sound and R’w will be discussed as well for the above mentioned configurations.