Signs of Success! (Was: Resilient Channel In Ceiling?)

I'm currently working with a builder on a design for a partial garage conversion for a drum practice/teaching studio. Thanks to this site (I think my eyesight has deteriorated significantly reading it over the past couple of months...) I think I've managed to tackle the question of wall design fairly well. Two external walls will be 1 leaf of brick/concrete block with an air gap and second leaf comprised of a stud wall with double plasterboard on the inside. The other two walls will be of double stud construction, double plasterboard on the outside and inside (different thicknesses on one side) with a significant airgap to help with Low Freq. Tran... MSM construction all the way, and enough acoustic caulk to gag an elephant. All seems good. Now comes the ceiling... The garage has existing timber framing at a height of 8' and and an angled roof that peaks at around twice that height. I'm considering simply adding two layers of plasterboard on the underside of the existing framework along with Rockwool Acoustic Slab above that. Should I be considering resilient channel in the ceiling? Am I going to gain a significant enough amount of transmission loss to justify it in such a situation? I notice that there are ceiling designs mentioned on this site both with RC and without. Can anyone pitch in their 2 pence on this one?

Well, I am no expert, but I am just going on what I have been advised and read about. I went with RC on a small part of a ceiling that I could not afford to lose any more height by creating a free-floating frame. Your isolation is only going to be as good as your weakest link. You could have solid lead walls that are 10 feet thick, and then if your ceiling is compromised, you might as well have not bothered with the walls. There were several times with my build where I started to take a shortcut somewhere, but then I was brought back to reality with the "weakest link" issue. If you have a big hole in your isolation, all of your other work is for naught. My advise, get the RC and do not skimp ANYWHERE! Good luck!

Fair enough. That's the way I was leaning, for exactly the reasons you stated. My detracting thought is that since there will be a minimum 6" and maximum 6-7 foot air gap between the "new" ceiling and the existing tiled roof (second leaf) that I wouldn't be gaining THAT much by hanging the new inner ceiling on RC. I suppose in the end the cost isn't that much different and I will - at the very least - gain some TL in the mids and highs; which in my case means snare drums and cymbals.

In order of VAlue - greatest isolation to least isolation: Independant ceiling RSIC clips RC-1 or 2 (I reccomend 2 for ceilings) Direct connect. Walls would be the same - If the ceiling has RC-1 clips then that is your weakest link - and will do a lot to determine your over all isolation value/ I wsould reccomend that you try to figure out a way to do an independant ceiling - and then opt for RSIC clips if that is not possible. Sincerely, Rod

Thanks Rod. (Got a lot of mileage out of your book, BTW...) I've considered an independent ceiling, but because the existing timber framing is at 8", I prefer not to cut into my headroom another 6 inches, though if the performance were to be significantly better, I suppose I'd have to consider it. I'm not familiar with the clips, but I'll see if I can find a UK supplier to see about cost. Thanks again.

Boomka77 wrote:

Thanks Rod. (Got a lot of mileage out of your book, BTW...) I've considered an independent ceiling, but because the existing timber framing is at 8", I prefer not to cut into my headroom another 6 inches, though if the performance were to be significantly better, I suppose I'd have to consider it. I'm not familiar with the clips, but I'll see if I can find a UK supplier to see about cost. Thanks again.

Why would you have to loose 6" - you can step the new joists up betwwen the old ceiling joist with no problem. I can usually get a new ceiling down to only 1 1/2" to 2" of loss. Rod

Ahhh, I think I see what you mean. You run the new joists in between the old joists and use the new stud walls to support it? Smart like the Dickens, that... Would you recommend decoupling the new joists from the new stud walls somehow? Neoprene or somesuch?

Boomka77 wrote:

Ahhh, I think I see what you mean. You run the new joists in between the old joists and use the new stud walls to support it? Smart like the Dickens, that... Would you recommend decoupling the new joists from the new stud walls somehow? Neoprene or somesuch?

No - the idea here is to decouple the new from the old - after that you gain nothing by carrying it further. By the same token - you do not use RC if you have independant frames - Rod

rod gervais wrote:

Boomka77 wrote:

Ahhh, I think I see what you mean. You run the new joists in between the old joists and use the new stud walls to support it? Smart like the Dickens, that... Would you recommend decoupling the new joists from the new stud walls somehow? Neoprene or somesuch?

No - the idea here is to decouple the new from the old - after that you gain nothing by carrying it further. By the same token - you do not use RC if you have independant frames - Rod

Thanks for the input. I'm going to go out and have a look at the existing joists tonight and come up with a plan to build amongst them. Two questions, however, if I can bother you some more... 1. When putting insulation into the new ceiling, will it be necessary to cut it so it sits on either side of the old joists? Is the density of compressed acoustic/fire slabs going to be a problem for transmission if I just squish it in between the new ceiling and the old joists? I know that insulation usually counts as "airspace", but is that still the case when it's severely compressed; if it will compress that much? 2. Do you close off the ends of the new joists to keep the insulation from shifting around (though I don't know how that would happen) or does it even matter? If you do, how do you manage that with the old joists in the way? I've searched and I can't find a diagram on the site of what we're talking about. But I seem to recall seeing one around here... Hmmm.... Anyone?

One additional question. How does one cap a double stud wall system when the two stud walls are a good distance apart - say 8"? Moreover, how do you cap and keep the airspace "airtight" when building a stud wall inside a brick or mortar wall? If the object is to decouple the new from the old?

Do a search here for firestop details that should answer your questions - I know they have been posted. Rod

Thanks, I wouldn't have thought of that. I know I've seen that kind of thing as well.

Here's a great detail for that condition.

rod gervais wrote:

Boomka77 wrote:

Thanks Rod. (Got a lot of mileage out of your book, BTW...) I've considered an independent ceiling, but because the existing timber framing is at 8", I prefer not to cut into my headroom another 6 inches, though if the performance were to be significantly better, I suppose I'd have to consider it. I'm not familiar with the clips, but I'll see if I can find a UK supplier to see about cost. Thanks again.

Why would you have to loose 6" - you can step the new joists up betwwen the old ceiling joist with no problem. I can usually get a new ceiling down to only 1 1/2" to 2" of loss. Rod

What a great idea. I never would have thought of that. So the old & new joist would be like interlocking your fingers. I guess you would need to have nothing in between those existing joists: duct, gas lines, wiring, etc. Very cool...

Just did my first test on my build. All the walls are 2 layers 5/8 sheetrock with greenglue on reselient channel with ultratoch, then concrete walls. The ceiling is the same except I used 2 layers of 1/2" sheetrock. The final seal was the double doors at the entrance. My studio is not up and running yet so I took the stereo out of the bedroom, about 70 watts with a 10" sub. I put it on the wood floor with no mat, turned it up about 3/4 with AC/DC. Total silence.

natas wrote:

Total silence.

Maybe the fuse was tripped............ :wink: Rod

:D Well, almost total :D I am very satisfied, now the wife can watch TV whilst I squeeze the life out of my Tele!

Thanks for the graphic, Rod. I have just one more question, unrelated to the ceiling of course. Insulation: I read here often that the optimum density for insulation is about 2.5 - 3 PCF, but elsewhere I've seen a table (created by you, Rod) showing that Rockwool RW3, which has a density of 60 kg^3 (closer to 4 PCF) is good bang for the buck across the largest frequency range. Can anyone chime in? There are a lot of products being touted around the UK these days - especially by Rockwool, etc. as there has been a lot of changes in the construction industry regarding sound isolation. The manufacturers have seized on this to have a field day advertising this product and that with all kinds of claims of benefit, but usually without any quantitative data to back it up. As such, even builders are a little bedazzled I think... Anyway, is there any benefit in using one of the denser products being bandied about, or is the 2.5 - 3 guideline the only way to go?

This is what I used; http://www.greenmakersupply.com/product ... page_id=66 lots cheaper and Green!

Boomka77 wrote:

Insulation: I read here often that the optimum density for insulation is about 2.5 - 3 PCF, but elsewhere I've seen a table (created by you, Rod) showing that Rockwool RW3, which has a density of 60 kg^3 (closer to 4 PCF) is good bang for the buck across the largest frequency range. Can anyone chime in? There are a lot of products being touted around the UK these days - especially by Rockwool, etc. as there has been a lot of changes in the construction industry regarding sound isolation. The manufacturers have seized on this to have a field day advertising this product and that with all kinds of claims of benefit, but usually without any quantitative data to back it up. As such, even builders are a little bedazzled I think... Anyway, is there any benefit in using one of the denser products being bandied about, or is the 2.5 - 3 guideline the only way to go?

Boom, actually, your mixing apples and oranges here - unless I went temporarily crazy at some point in time that table you are referring to was a comparison of products for room treatments.......... not for in wall insulation. For insulation I recommend the standard fluffy fiberglass (roughly 1.2 pcf) you loose a little bit on the higher frequencies (as far as TL value goes - but you gain in the bottom end - check out IR-761 if you wish to verify this for yourself. The more dense the insulation product - the lower the TL values will be in the LF range. Rod

Rod, You're right, I went back and checked the post you'd made (on another forum) regarding insulation density and you were indeed talking about room treatments. In all the reading I've done on this, I got some wires crossed. Sorry to misquote you. But I do find it interesting that you're suggesting a density as low as 1.2 PCF versus something like Rockwool between 2.5 - 3 PCF which has been touted elsewhere on this site. So, the difference is in the low end?!? Oh boy.... :( I just finished agreeing to a quote from my builder using Rockwool RWA45 (40kg/m^3 or 2.5 PCF) and thought I was doing the right thing. Should I change that? I am trying to isolate drums, so low end is of great concern. So far the construction is this: Wall 1) Single layer brick - 2" Air - RwA45 - Wood Studwork - 2 x 15mm (5/8") Plasterboard Wall 2) 4" Solid Concrete Block - 2" Air - RwA45 - Studs - 2 x 15mm plasterboard Wall 3) 2 x 15mm plasterboard - Studs - RwA45 - 4" Air - RwA45 - Studs - 2 x 15mm plasterboard Wall 4) 2 x 15mm plasterboard - Studs - RwA45 - 1" Air - RwA45 - Studs - 2 x 15mm plasterboard Ceiling - Independent resting on inner stud wall, 2 x 15mm plasterboard and RwA45 - air - pitched roof (felt and tile) Should I have him downgrade the insulation to something less rigid to help with low end?

Yes, you should - 20 million Canadians can't be wrong :wink: Inside a wall, the main function of insulation (sound-wise) is panel damping and (to a lesser extent) absorption - you do NOT want anything between wall panels that will hard couple them, which higher density tends to do - In any and all wall testing I've seen, higher density can improve TL at UPPER frequencies but HURTS it at LOWER frequencies - just a personal theory, but I tend to think this may be (in part) because the denser stuff might be causing the wall to act somewhat as a "3-leaf" construct. Warning - this is, at this time, just a "gut feel" on my part, but the FACT is that lower density INSIDE a wall helps low frequency TL. Since it's MUCH harder to stop lows than highs, it only makes sense to build a wall for best LOW frequency TL - by doing this, you will automatically build enough HIGH frequency TL into the wall. For acoustic TREATMENT inside a room, it's a whole different animal - and it's hard NOT to get confused at first since BOTH applications use "insulation", and NEITHER application is using the stuff as it was originally intended :roll: HTH... Steve

Heh... It's true, we Canucks are seldom wrong, though I sometimes question my relocation to the UK when I'm costing out my project! ;) Anyway, I changed my post above. The Rockwool product I'm looking at is somewhere in the range of 2.5 PCF (using the 40kg/16 calculation mentioned elsewhere on this board). Do you suppose that's still too dense? I hope my builder hasn't ordered the insulation, yet... I don't want him to think I'm messing him about... ;)

you want material in the 1.2 to 1.6 pcf range.

Alright then... So for those of us in the UK, somewhere between 19 and 26kg/m^3. I'll hunt for some specs on products available in the UK and make it so. Though I'm a little embarrassed to be making this revision after being VERY specific with him about the insulation already, but such is life. Haha... I'm paying him, I guess. ;) Thanks Rod, and Knightfly, for your input.