What are the Sound Transmission Class (STC) ratings for concrete and masonry walls?
The actual Sound Transmission Class (STC) for your wall will depend on the type of wall, the finish, and the weight of the wall per square foot of surface area. STC ratings for partition materials may range from 40 to more than 60 with higher values providing less sound transmission. The Federal Housing Administration (FHA) requires a minimum STC of 46 to limit sound transmission from unit to unit in multi-family dwellings.
See the table below for details. For example, a 4 in. masonry wall at 18 lb/ft2 would be rated at 40, while the same thickness of wall with a weight of 27 lb/ft2 would have a rating of 45. An example of a painted wall (both sides) weighing 22 lb/ft2 is rated at 43.
Question and answer courtesy of Portland Cement Association (PCA). More information is available at: http://www.cement.org/tech/cct_faqs.asp.