resilient channels - how far apart to mount?

[dr_penner]

Hi again everyone,

I am soon to mount my ceiling drywall and resilient channels to the floor joists above my room. I have questions:

1) How far apart should the channels be mounted? The Auralex RC-8 info says 2 feet apart or closer. I plan for 16". Is closer equal to more load carrying capacity?

2) How many layers of drywall can be held up by these channels? The Home Depot guys say one layer only (5/8" drywall). Auralex says two. Others say three.

3) Does anyone have trouble getting the screws to easily penetrate the channel? One person posted that he couldn't get the screws to fully sink into the drywall because they would spin in the channel.

Thanks!

Kurt Penner

[ausrock]

dr,

Read through the following thread............specifically Knightfly's post..............http://www.homerecording.com/bbs/sho...ight=resilient

Alternatively, contact the sheetrock, etc., manufacturers or find their websites and get the information direct from them. DON'T rely on the guy working at Homedepot or the like to have adequate product knowledge.

[DigitalDon]

I'm not sure if it applies to ceilings but here are the specs for wall mounting RC: If the studs are 24" on center then space the RC 16" apart. If studs are 16" on center then space the RC 24".

DD

[John Sayers]

It also depends on how much weight you want to hang on them The more weight/layers the closer the RC.

cheers
John

[dr_penner]

Thanks for the replies.

I decided to go with 12 inch spacing for the RC channels. I planned initially to go with one layer of soft fiberboard and one layer of 5/8" drywall, but I wanted the option of adding one more layer (1/2" drywall) if I felt it was needed.

Plus I like to overengineer anything that might crash down on my head..... ;->

Kurt Penner

[John Sayers]

If you want to use the soft fibreboard it should be sandwiched between the drywalls, I wouldn't start with it.

cheers
john

[knightfly]

Kurt, first of all John is right on about NOT putting the sound board first -

Second, your question "One person posted that he couldn't get the screws to fully sink into the drywall because they would spin in the channel."

If you find yourself in this situation, you may have the wrong type of screws, your RC may be kind of wimpy, not sure - what I would do in that case is to use a screw gun with a depth stop (usually a hollow nose you adjust to slip the clutch when the screw is in far enough) and I would DIMPLE the wallboard and THEN drive the screw in the center of the dimple. This will put the screw head deep enough to mud and/or add the next layer, hopefully WITHOUT stripping the screw in the RC.

If more than a couple screws spin like this, you have NO HOLDING power - you need to find a way around that problem unless you LIKE wearing ceiling on your head.

Also, if planning on three layers on RC, I would center the fasteners for EACH LAYER on 9" (this is a CEILING), offsetting each course by 3" so they don't coincide, and using successively longer screws per layer so they will pass thru the RC by at least 1/2", possibly 3/4".
Don't forget to orient the middle layer at 90 degrees for best seal.

Hope that helped... Steve

[Chadwick]

I purchased RC and selfdrilling screws from Home Depot and had a problem with the screws spinning in the channel as well. I tried using standard COURSE thread dry wall screws and I had no problems after that. The other advantage using standard drywall screws in my situation was that they actually penetrated the channel with less effort than the self drilling screws. This method might not work as well on other types of RC.

Chad

[John Sayers]

LDQ - Luis should be able to help on this one as he's just done it for his S. Productions studio at the construction site.

cheers
john

[sjoko2]

Most likely a too late response but..........
I have found the best results with first a layer of 1/4" firerated drywall, then a layer of 1/2" soundboard, and finished with a layer of 7/8" firerated drywall, on 9" centers, stacked, as was already suggested.

[knightfly]

Sjoko, I haven't tried that combo but it sure make sense - you've got 3 different thicknesses, 3 different resonant frequencies, and 2 different types of material - if that doesn't create a broadband barrier, I don't know what would.

Have you done any testing that produced STC or MTC ratings, or do you just find that it's quieter than other combo's youve tried? Steve

[sjoko2]

I gathered some data a few years back.......... but can't find it anymore.
However, I have used this approach in three projects now, one of them being in a timber clad building near a railway line, with very good results, better results than using for instance 2 layers of 5/8" or even 2 layers of 7/8", and it is lighter as well.
Please note that there is a special "high density sound board" drywall product available, which is the 1/4" one.

[Roker1]

Originally posted by knightfly

Don't forget to orient the middle layer at 90 degrees for best seal.

Hope that helped... Steve

Sorry I know I'm late on this one, but just wanted to clarify with you Steve.....what exactly do you mean by
"orienting the middler layer at 90 degrees"??

thanks steve..

cheers

[knightfly]

If you put three layers of 4 x 8 foot panels on a wall, and all three layers are placed with the long (8') dimension running the same way (like, vertical) there is more of a chance that cracks between boards will co-incide, causing sound leakage.

So, if you put the first layer on running vertical, then the second layer horizontal, then the third layer vertical again (offsetting by 2' from the first layer by starting with 1/2 sheet) then you have no coincidence of joints anywhere.

I used a wall for example to avoid the confusion that could result by a ceiling being ALL horizontal, in a way. The same method applies, however - you just would run one course with the long way North, the next course East, and the third course North again, but starting with 1/2 sheet (cut lengthwise) again.

Sjoko, thanks for the clarification on your choice of materials/thicknesses - doing it that way sure sounds like a good way. There's no test like "Does it work?"... Steve

[Roker1]

thanks heaps steve....so you sort of create crosses in a sence...
on top of one sheet that's 8' high, you'd put two 4' sheets..right??
and the one 8' sheet on top of those two....

thank you

[knightfly]

Right. If you run the first course with the sheets vertical, screwed to horizontal RC, you would run the second course horizontal, offset horizontally from the first one by one stud (either 16" or 24") so that the cracks don't line up - then, if you use a third layer, go back to vertical, and again offset the cracks, even from the first layer. Doing this gives the longest path for any sound that may leak between layers, which shouldn't happen because you're caulking as you go - it's more precautionary, but also makes for a slightly stiffer wall by not having joints coincident from layer to layer.

You accomplish the offsets, merely by starting the next course one stud away from the last crack - then, you cut a piece to fit the gap you left at the beginning of that course.

Hope that confused the matter even more :=)

[Roker1]

Originally posted by knightfly


Hope that confused the matter even more :=)

it did actually ....nah pretty clear now....
thanks steve

cheers