"Many builders are insulating these walls fully for sound proofing purposes per the International Building Code (IBC), Section 1207, Sound Transmission walls, partitions, and floor/ceiling assemblies separating dwelling units from each other must have a sound transmission class (STC) of not less than 50 for airborne noise when tested in accordance with ASTM E 90."
Also the comment I replied to said 'americans' not 'in america'
These sound like wild assumptions with nothing to back them up.
https://basc.pnnl.gov/code-compliance/air-sealing-and-insula...
"Many builders are insulating these walls fully for sound proofing purposes per the International Building Code (IBC), Section 1207, Sound Transmission walls, partitions, and floor/ceiling assemblies separating dwelling units from each other must have a sound transmission class (STC) of not less than 50 for airborne noise when tested in accordance with ASTM E 90."
Also the comment I replied to said 'americans' not 'in america'