Question:

• What is a wall / partition system with good sound insulation rating ?

   

Answer:

• The average sound insulation level of a wall system is rated by a single figure called STC, sound transmision class, under American standard ASTM E90  or Rw, weighted sound reduction index, under international standard ISO 140-part 3 (recently replaced by ISO 18233). These two rating methods are slightly different with the former based on the 125Hz - 4000Hz frequency range and the latter based on the 100Hz - 3150 Hz frequency range. In general, for most of us, the difference can be ignored. For instance, a purpose-built wall system has an STC 50 when rated by the American standard, whereas achieves an Rw approximately equals to 50 dB(A) when rated by the ISO standard. For most wall systems of exactly configurations, their STC and Rw rarely deviate more than 2 measuring units.
  

   

• A 100mm thick hollow brick wall with its weight approximates to 140-150kg/m2 will have a maximum Rw = 42 dB(A); a 100mm thick solid brick wall with its weight approximates to 210kg/m2 will have a maximum Rw = 46 dB(A); and a 100mm  thick solid concrete wall with its weight approximates to 240kg/m2 will have a maximum Rw = 50 dB(A). Whereas an internal drywall partition of a 102mm total thickness and 46kg/m2 weight, constructed from light gauge steel studs and tracks, both sides lined with two layers of 12.7mm thick fire rated wallboards, with 50mm thick 14kg/m3 glasswool insulation fit snuggly between the frame, if installed carefully in compliance with internationally good practice (correct design, high quality materials, highly skilled workers, strict supervision) may achieve Rw = 50-51 dB(A). From above facts and figures, we can see that with its weight only approximates 19% of that of a dense concrete wall of the same thickness, a gypsum drywall partition has similar sound insulation performance !!!
  

   

• Under the Building Code of United Kingdom, for multi-residential apartments, the minimum weighted sound reduction index of separating walls (wall that separates one apartment from another) must be Rw = 55 dB(A), while that of an internal partition that divides one area from other area, for instance a bed room from a living room, or a bed room from a toilet, of the same apartment must be Rw = 50 dB(A).