The STC requirements apply to exterior walls as well as interior partitions (walls, ceiling and floor). Meeting the requirements usually requires insulation between interior common walls, double layers of gypsum or acoustical drywall on at least one side

The STC requirements apply to exterior walls as well as interior partitions (walls, ceiling and floor). Meeting the requirements usually requires insulation between interior common walls, double layers of gypsum or acoustical drywall on at least one side of the wall, air gaps between common walls, sound-rated doors, and sealants around penetrations and door openings.