The 2015 edition of the National Building Code of Canada (NBCC) introduced significant changes to the requirements for the acoustic separation between dwelling units. While the requirements in previous editions of the NBCC were given in terms of the sound transmission class (STC) rating, the new requirements in the 2015 edition are given in terms of the apparent sound transmission class (ASTC) rating. The STC rating is based on laboratory measurements and only describes the sound transmission through a single building element. The ASTC rating quantifies the sound insulation of the complete building system, i.e. taking into account sound transmission through the separating element and sound transmission via flanking paths such as common floors or ceilings. The ASTC rating is therefore a better descriptor for the sound insulation that the building occupants will actually experience.
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