Section 3280.115 - [Effective 3/17/2025] Sound transmission between multi-dwelling unit manufactured homes(a)Scope. This section applies to common interior walls, partitions, and floor/ceiling assemblies between adjacent dwelling units.(b)Air-borne sound. Walls, partitions, and floor/ceiling assemblies between stories separating dwelling units from each other must have a sound transmission class (STC) of not less than 34 for air-borne noise when tested in accordance with ASTM E90 (incorporated by reference, see § 3280.4 ) or calculated. Penetrations or openings in construction assemblies for piping; electrical devices; recessed cabinets; bathtubs; soffits; or heating, ventilating, or exhaust ducts must be sealed, lined, insulated or otherwise treated to maintain the required ratings. This requirement does not apply to dwelling unit entrance doors; however, such doors must be tight fitting to the frame and sill.(c)Structure-borne sound. Floor/ceiling assemblies between stories separating dwelling units must have an impact insulation class (IIC) rating of not less than 34 when tested in accordance with ASTM E492 (incorporated by reference, see § 3280.4 ).