ISO 12354-2:2017 specifies calculation models designed to estimate the impact sound insulation between rooms in buildings, primarily using measured data which characterize direct or indirect flanking transmission by the participating building elements and theoretically-derived methods of sound propagation in structural elements.A detailed model is described for calculation in frequency bands, in the frequency range 1/3 octave 100 Hz to 3150 Hz in accordance with ISO 717‑1, possibly extended down to 1/3 octave 50 Hz if element data and junction data are available (see Annex E); the single number rating of buildings can be determined from the calculation results. A simplified model with a restricted field of application is deduced from this, calculating directly the single number rating, using the single number ratings of the elements; the uncertainty on the apparent impact sound pressure level calculated using the simplified model can be determined according to the method described in ISO 12354‑1:2017, Annex K (see Clause 5).ISO 12354-2:2017 describes the principles of the calculation scheme, lists the relevant quantities and defines its applications and restrictions.