Help with insulation

[lodstudios@gmail]

I am battling REALLY old construction right now, it is basically 2 1/2 by 3" stud framing. I beefed up the inner walls with 1/2" plywood and am going to insulate now. Problem is, I am left with 2.5" space to put the insulation which is roughly 3.5". I am planning on using RC-13 for the walls but that leaves me with only 3"...I am assuming I can't compress the insulation, without losing the R value, a half an inch so I have to go with something smaller. Right? What do you think my options might be?

Here is a link to my build.

Best,
Keith

[gn87berner]

Just stuff what you have in there.It will be fine. It will bulge and touch the drywall adding dampening. A Good tip is to pop your lines where your channel will go before insulating so your bulging insulation won't interfere. Otherwise it will difficult to get lines on studs.

[lodstudios@gmail]

Ok, good idea!

Thanks so much!

Keith

[Ted White]

R11 would be better. Best to not compress.

The damping is a good idea, but consider using an actual damping material.

[gn87berner]

John Sayers' Recording Studio Design Forum • View topic - Floating floor over basement concrete. (Artifact Recording) here's a link that says it's beneficial to have your insulation touching your inner wall. It'll act as dampener without any extra cost. For weather uncompressed is superior but just go for it. INMO compressing that 1 inch won't hurt a thing and it will make sure your insulation will bulge out and make contact with your inner wall. Good luck

[Ted White]

I agree compressing some isn't bad, but there would be little if any actual damping to the drywall panels.

[KyleDiSanto]

It will help dampend the drywall a little bit, HOWEVER, when you compress insulation, you DO NOT get its full "R" Value.

Hence whey I'm guess Ted Suggested R11

In your case, R-13 might be easier to get, I don't know...in which case I would just stuff it in there.

[gn87berner]

Being in beautiful San Diego, losing a little R-value shouldn't be a problem. Plus any decoupling will help in the prevention of conduction regarding transfer of heat. From my understanding, half way down the page Knightfly suggests your insulation lightly touch inner wallboard will act as a dampener. Similar as to lightly touching a resonator head on a drum and tapping the drum head. The resonator is not able to freely vibrate therefore dampening. When you put up your rc-channel, it will hold in your insulation = good. If it bulges a little to far out, use staples thru the plastic banding that comes on insulation batts when sold in 3's, and strap it in a little more. You can find the stuff on most const. sites or dumpsters. Again good luck.

[Ted White]

I'm hoping no one is designing rooms around the damping capacity of lightly contacted insulation. There is a huge amount of energy coursing through these panels as bending waves. The insulation contact does not provide a sink to remove this energy.

[gn87berner]

Not to design a whole room around this. Just if you insulate anyway, it's better to have it touch rather than hold it back. This and this alone isn't going to cut it. In the same post I referred to, he lists all the important facets of isolation. Or go to green glue site and they list isolation attributes, mass,decoupling,absorption,resonance and conduction. Now if you believe having something touching the inner wallboard will dampen,lower resonance, like knightfly suggests go for it. If not don't. It is free after all.

[Ted White]

Let me clarify my point so as not to appear confrontational. In a wall or ceiling application, the light contact of insulation would technically damp. Technically.

Then comes the practical. Can you measure the damping, and / or can you hear any improvement?

Technically some amount of damping must occur. Practically, no damping occurs.

Looking at the NRC research, IR 761, they studied the placement of insulation in a cavity. Contacting surface #1, placed in the centre of cavity (no contact of surfaces), and contacting surface #2. No difference in performance. There's no practical benefit to having the insulation contact one or both surfaces.

It's really dificult to successfully (practically) damp the leaves of a wall or ceiling.

Having insulation in the cavity will damp cavity resonance. Won't actually damp the panel.

[gn87berner]

Ted.. could you point out what page in IRC 761 the data is on. I couldn't find where they had the insulation touching and then not touching the surface. I also couldn't find where they had the insulation in the middle. Thanks. I think this has gotten way blown out. If there's a good reason to not have insulation lightly touching your inner wall I would be all ears. It has to do something, touching. As it can not do nothing. Science won't allow it. And I don't think anyone has actually tested "lightly touching" against "definitely not touching". All the data on 761 just says "in this cavity." To me it doesn't matter what anyone else does, I'm having mine lightly touch, because it "has to do something" measureable or not and that makes feel better. Not that I'm designing my studio around this.

[Ted White]

Apologies. It's IR-766:

"Moving 152 mm glass fiber batts from the top, to the middle and then to the bottom of a 240 mm deep cavity had no significant effect on sound insulation."

The world won't end if the insulation is lightly touching. Indeed most walls or floors that we all discuss have insulation touching one or both leaves. My only point was and is that you can't expect any practical damping to result.

The issue is that so many casual readers pick up on these things and don't ask further questions. I would hate to have a lurker read into this that this is a design goal.

I'm sure your build will go well.

[lodstudios@gmail]

Wow, sorry guys...didn't mean to ruffle any feathers! But, this is EXACTLY why I come here.

Thanks all, I will insulate with the R13.

Best!
Keith

[Bassmankr]

I thought that R13 was more fiberglass for the 3 1/2" thickness (more dense) than the less expensive R11. If so compressing the R11 stuff a small amount might bring it up to a R13 insulation value. Anyone?

[Ted White]

Good point. You're saying that if you have R13, but compress (and compromise) it a bit, you may as well go for the R11.

Can't argue with that at all.

[666666]

Originally Posted by lodstudios@gmail

...Problem is, I am left with 2.5" space to put the insulation which is roughly 3.5"....

I personally would have faced all the studs with 3/4" furring strips so that your space would grow from 2.5" to 3.25".... then the 3.5" insulation would fit a lot better / go in way easier. Trying to compress 3.5" insulation by 1" can be slightly tough over a 4'X8' area (when screwing up a 4'X8' drywall panel), it can be done but it's a little bit more of a pain than you might initially think. Also, if you "expand" your studs to 3.25" (from 2.5"), you'll get a little bit more R value and sound isolation. Furring strips are pretty inexpensive and you could slap them up in maybe under two hours or less so it's not too much work / expense to make it happen. You could probably do it faster than it will take to finish reading / responding to this thread over the next few days. And at 3.25", you'll still have a little extra dampening too for good luck.

[gn87berner]

For anyone interested nrc-ir-766 doesn't address the issue we are talking about. 1st.. They state "insulation at the top, middle, or bottom showed no difference" The thing is you can have insulation at the top, without it touching or the bottom without it touching. They weren't testing what we are talking about. Also 766 is "testing joist/ceiling assemblies with a tapper" This is for impact noise/footsteps. On the 2nd or 3rd page of the summary they state "using insulation/absorption material show no difference in assemblies that did not use resilient channels" Now if you go to the link below, the first example is where putting insulation in wall cavities shows between 4 and 5 stc gain. http://www.stcratings.com/assemblies.html..We need something different than 766. I do not have any data saying it will "add dampening" Nor have I seen any data thus far proving "it virtually does nothing" I would love to see some one with some real data on this subject. So I apologize for passing on information that is considered common knowledge in some circles, but that I can't prove. I'll be more careful in the future.

[Ted White]

I think you've brought a thought provoking perspective to the topic. I think its very interesting. I appreciate you discussing it with me.