This update explains how to achieve effective control of sound transmission through gypsum board walls in multi-family dwellings. The information is derived from the results of an exhaustive industry-supported research project conducted by NRC’s Institute for Research in Construction (IRC).
The research project studied the influence of isolating each face of the wall, and of mass, sound absorption and cavity depth on controlling sound transmission through walls. Because the STC between dwelling units was increased from 45 to 50 in the 1990 edition of the National Building Code, this article focuses on the role and relative importance of these key parameters in constructing walls that can attain STC ratings of 50 or more.
The research demonstrated that the major factor to consider in constructing walls to control sound transmission is the isolation of the gypsum board layers on each face of the wall. If at least one of the layers is not resiliently supported, or if the two faces of the wall are not isolated from each other, sound-absorbing material in the cavity is rendered ineffective. When the layers are isolated, sound transmission through the wall can be reduced by increasing the mass, the cavity depth and the amount of sound-absorbing material.
To provide the needed isolation, walls can be constructed of double studs (wood or steel), staggered studs (wood or steel), nonload-bearing steel studs, or wood or loadbearing steel studs with resilient channels.3
The type of sound-absorbing material has a relatively minor effect on the ability of the wall to control sound. There are clear benefits associated with increasing the spacing between studs and resilient channels – the farther apart they are, the better the sound reduction. Usually the STC increases by one or two points when going from 400-mm to 600-mm spacing.