Rw (Weighted Sound Reduction Index)

Rw is the internationally standardized single-number rating for airborne sound insulation of a building element, defined in ISO 717-1:2020. It is determined by fitting a reference curve to the measured sound reduction index (R) in third-octave bands from 100 Hz to 3150 Hz using the same methodology principle as STC but with a different reference curve and frequency range. Rw values are reported with spectrum adaptation terms: Rw(C;Ctr), where C adjusts for A-weighted pink noise (general living noise) and Ctr adjusts for A-weighted traffic noise (emphasizing low frequencies). Typical values include Rw 33 for single glazing, Rw 45–50 for standard plasterboard walls, and Rw 55–65 for high-performance separating walls. Building codes across Europe (EN 12354), Germany (DIN 4109), and internationally (ISO 717-1) specify minimum Rw values. The combination Rw + Ctr is increasingly used for facades exposed to traffic noise because standard Rw underestimates low-frequency performance requirements.