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)

How Loud is TOO LOUD

Standards set by OSHA (Occupational Safety and Health Administration) indicate that continued exposure to noise over 85 dBA will eventually harm hearing. According to OSHA, the exposure time allowed is cut in half for every 5 decibel increase. For example, if a sound is 95 dBA, then 4 hours of exposure, over time, will cause hearing loss, and exposure to sounds at 115 dBA for just 15 minutes a day, over time, will cause hearing loss. Other groups, such as NIOSH (National Institute for Occupational Safety and Health) calculate safe exposure time by decreasing time in half for every 3 decibel increase. The NHCA (National Hearing Conservation Association) is an excellent resource for more information about occupational hearing conservation programs.