STC Ratings Simply Put

Sound Transmission Class (STC) is an integer rating 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. Compressing a batt reduces STC and thermal efficiency

• Stud assembly must span from deck to ceiling

• Structurally decoupling the gypsum wallboard panels from each other, like using a staggered stud assembly

or a double stud wall) can yield an STC as high as 63 or more

•Also materials such as United Plastics Corporation's dB-3PRO along with gypsum wallboard and insullation may also improve STC ratings (Refer to manufacturer specifications)