he international standard ISO 140-5 for the measurement of the sound insulation of build- ing façades will soon be replaced by the new standard ISO 16283-3. This revision includes the procedures for measurements at low frequencies down to 50 Hz. The uncertainty of fa- çade sound insulation, in particular at low frequencies, was evaluated by a Round Robin Test, conducted in a full-scale experimental building at ITC-CNR. Each of the 10 teams in- volved in the RRT replicated the tests 5 times, for a total of 50 measurements. The different measurement positions inside the receiving room are compared. In particular, all the teams involved in the RRT assessed corner and center room positions; their energy average values according to ISO 16283-1 are considered and the relative uncertainty in terms of repeatabil- ity and in situ reproducibility standard deviations are compared with the ones measured and calculated following ISO 140-5.