As part of an ongoing research project in the new four-room flanking facility at the National Research Council Canada, the velocity level differences between cross-laminated timber floors/ceilings and lightweight timber framed walls have been measured according to the standard, ISO 10848-1. The apparent sound reduction indices between the pairs of rooms have also been measured according to ISO 10848-1. The measured apparent sound reduction indices are compared to those predicted according to the standard, ISO 12354-1 based on the measured velocity level differences, the resonant transmission losses and the dimensions of the elements of the flanking paths between the room pairs.