Low Cost and Easy Soundproofing Solution instead of Drywall and Resilient Channel: QuietRock
The advent of high quality audio systems and home theaters has changed the building environment completely. Where hotels, motels, homes, condos, and apartments previously only needed to deal with isolating a neighbor’s voice, we must now contend with loud movies coming from next door, even when the sound is simply coming from a good television. Given today’s need for high quality transmission loss in walls, it is important to rethink the original standards of Sound Transmission Class (STC) 34 walls and start thinking about raising the transmission loss by 20dB – 30dB or more, to provide a high quality living environment for all.
Over the years, many techniques have been used to enhance the sound transmission loss through residential and commercial walls. Many of these methods require unusual or difficult construction techniques that may not be followed accurately by an installer. As technology has given way to new materials, the more exotic construction techniques can revert back to standard STC ratings for single wood or steel stud construction. Furthermore, new technology allows easy, fast, and low cost retrofitting in existing structures (including homes and offices) where the existing installed drywall does not have to be removed to achieve large increases in Sound Transmission Class (STC) ratings. Most importantly, this guide draws from actual lab and field testing on complete assemblies–it is important to prove how well a specific wall assembly performs. Serious Materials is committed to industry standard STC testing on complete assemblies and references independent lab tests throughout this guide.
Interior Walls Using Traditional Technologies
Walls with higher STC values have been achieved for years using a variety of construction techniques.
A commonly used technique since the 1960s, on both wood and metal studs, is called resilient channel (RC). These are metal channels that are placed at right angles to the studs. The drywall is then screwed into the channel, being very careful that no screws touch a stud directly. In this way, the drywall is isolated from the studs, thus carrying less noise and vibration to the outer wall.
When installed correctly, RC can typically improve STC ratings by 8-14 points, depending on construction. An important note here is that resilient channel is easily “short-circuited”, or in other words, the isolated sheet of drywall can lose some of its isolation due to mechanical connections between the drywall and the frame or adjacent wall/floor/ceiling. For this reason, very careful construction techniques must be followed. For instance, no screws can ever touch a stud; drywall must not touch floors or adjacent walls or ceilings; no pictures or shelves can be hung on the wall where the fastener screws into the studs, etc. If there is one failure, it can ruin any gain that would have been had. Very careful construction and review by the architect or acoustic engineer is required.
Other stud arrangements, such as staggered-stud and double-stud increase STC points as well (covered below), but consume valuable space and can nearly double the labor costs in both wood and steel stud construction. For retrofit in existing construction, there have been few choices that do not require demolition. It should be noted that adding resilient channels to an existing wall (over the existing gypsum) will not increase STC values. There is not enough space between the old and new gypsum for RC to work effectively.