The objects of the study are lightweight enclosing structures (partitions) located between the premises of buildings. The surface density of lightweight fences lies in the range of 20 < μ < 100 kg/m2. The elaboration of methods for calculating the sound insulation of lightweight enclosures, taking into account geometric and physical and mechanical parameters, is an urgent task for building acoustics. The studies are carried out on the basis of the theory of self-consistency of wave fields with account of the resonant and inertial sound transmission through the enclosures. The article presents the results of theoretical studies of sound insulation of lightweight enclosing structures in the frequency range from 50 Hz to 5000 Hz. It was proposed to divide the generalized frequency characteristic of the sound insulation of lightweight enclosing structures into two ranges, the boundary between which is determined by the geometric sizes of the fence. Based on the theory of self-consistency of wave fields, a method was developed for calculating the sound insulation of lightweight enclosing structures in the frequency range above the threshold frequency of sound field diffuseness in the plane of the enclosing structure and below the threshold frequency. The method enables calculating the sound insulation of lightweight enclosures, the threshold frequencies of the areas of resonant sound transmission, as well as the frequency characteristics of the coefficients of resonant and inertial sound transmission. The implementation of this method is considered on the example of a lightweight frame-sheathing partition with anti-resonance panels. The authors obtained theoretical frequency characteristics of the coefficients of sound transmission through a lightweight frame-sheathing partition and the frequency characteristics of the sound insulation of the partition in the calculated frequency range.