Submitted by Jim Nisted, Dryvit Systems, Inc. for publication by CSI 8/23/2016
Originally published on Technical Services Information Bureau in October, 2012.
Sound Transmission Class (STC) is an integer range of how well a framed wall attenuates sound
- Doubling the mass of a wall assembly does not double the STC
- An empty framed wall (steel studs and a layer of gypsum wallboard on each side) has an STC of approximately 35dB
- Adding an additional layer of gypsum wallboard (from two sheets to four sheets) increases the STC by about 5-6 points
- Adding cavity insulation increases the STC approximately 4-6 dB
- Fiberglass batts increase the STC to 39; Cellulose insulation increases the STC to 44
- Batt insulation must fit tight without gaps
- Batt thickness provides better sound control than batt density.
- Stud assembly must span from deck to ceiling
- Structurally decoupling the gypsum wallboard panels from each other (using resilient channel, a staggered stud assembly or a double stud wall) can yield an STC as high as 63 or more
- Other materials such as mass-loaded vinyl (MLV), “soundproof” gypsum wallboard, or liquid applied dampening compound may also improve STC ratings. (Refer to manufacturer specifications
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