The pitfalls of Resilient Channel
Most contractors today are aware of a building product known as resilient channel, it is also referred to as "Chicago Bar" or R.C. It is a thin 20 to 25 guage galvanized steel channel that has a small flange to screw it to the studs or joists and a wider flange that the drywall is screwed into. It looks like an "L" or a "Z" channel. These channels generally are 3/8" (give or take) off of the face of the studs or joists and hold the drywall suspended and isolated from the studs/joists as well as the adjoining walls/ceiling. There must be a 1/4" gap around the edge of the newly installed drywall all the way around the perimeter where the drywall does not touch the adjoining walls or ceiling. This gap must be caulked in with an acoustical caulk or a combination of acoustical caulk and backer square. Backer square is a foam roll material 1/2" square and is similar to backer rod (which is round) and is used to help fill in the 1/4" gap around the perimeter of the drywall. It is best to get a backer square that is made of vinyl nitrile closed cell foam, that way you are not simply filling in this gap, but are adding to the soundproofing.
Many contractors and home improvement DIY folks drop the ball right here. They are not aware of just how important this gap really is. The 1/4" gap is imperative in order to keep the newly floated wall or ceiling from contacting the adjoining structures and shorting out the entire assembly. The key is to completely isolate the floated wall or ceiling from the studs/joists as well as the adjoining walls, floor and ceiling. Isolation is what you need when employing a floated ceiling or wall system. The 1/4" gap can not be compromised, it must completely isolate floated assembly from the surrounding structures.
The other area where mistakes are often made is when the drywall is being screwed into the R.C. If only 1 screw goes through the drywall into the channel and then screws into a joist or stud, you have short circuited any soundproofing you might have gotten from the floated wall or ceiling.
There are 2 types of Resilient channel, RC-1 and RC-2. There are others, but these are the 2 most common used today. The RC-2 is similar to the RC-1 except for the fact that it has 2 screw in flanges as opposed to just 1. The RC-2 is generally used in ceiling floats because it is much more stable. Keep in mind that with any floated ceiling assembly the RC is completely weight bearing. This holds true for sound clips and furring channels as well, but we'll talk about them at another time.
I hope this helps you to understand the basics of R.C. and though it is not the most effective sound isolator, it is the most widely known.
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