How do you soundproof a foundation wall? (ITOLLTHW Theater Build) - AVS Forum
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post #1 of 16 Old 10-27-2013, 06:32 AM - Thread Starter
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I have 2 walls of my HT which are poured concrete foundation wall (FW) - the top of this wall is about 6.5 feet from the floor and the joists rest on the top of this wall
Currently I have my ceiling (whisper clips, hat channels, DW+GG+DW+GG+DW) resting on the ledge

I've read here that despite the great mass of this wall, it can present flanking issues (sound going up the wall, through the rest of the house - even the other side) - and that it requires a framed stud wall filled insulation between the study and with DW+GG+DW in the front, and DW in the back, and that this wall should ideally be 1" from the concrete (and no less than 1/8" away) so that it doesn't come in any contact with the concrete as it vibrated (thus decoupling the wall from the concrete)

Questions:
Q - How do you put DW on the back of the stud wall if there's only 1" of space between it and the FW?
Q - Is it worthwhile to put DW+GG+DW on the back?
Q - I've already built my ceiling (see above) - so how do I anchor the stud wall?

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post #2 of 16 Old 10-27-2013, 06:53 AM
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Quote:
Originally Posted by cgott42 View Post

Q - How do you put DW on the back of the stud wall if there's only 1" of space between it and the FW?
You don't.
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post #3 of 16 Old 10-27-2013, 07:07 AM - Thread Starter
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Even better! so is the back totally bare (i.e. nothing between the R13 inside the stud wall and the FW)
or do I glue rigid insulation boards to provide a vapor barrier and add'l sound containment?
If I put the rigid insulation boards - (a) do I separate these boards by an inch or can the stud wall run right up to the them? (b) Also is it OK if the R13 is backed or is there a problem with 2 vapor barriers?
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post #4 of 16 Old 10-28-2013, 12:23 PM
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2" Rigid Foam (or spray foam)
1" air gap
2x4 stud wall

fill stud wall cavities with fiberglass (unbacked)
no further vapor barrier

This is basically BSC basement methodology.
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post #5 of 16 Old 10-28-2013, 12:44 PM - Thread Starter
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Since the back of the wall is open , what holds the unbacked insulation that's in the study wall in place?
Also - being that I already have standard R13 paper backed - is that a problem ?
i.e. how much of a problem is it? Also (for my own knowledge)- what is the reason that the 2nd paper / vapor barrier is a problem, and not added benefit?

thx
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post #6 of 16 Old 10-28-2013, 02:28 PM - Thread Starter
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My First Oops - Didn't hold onto the inner pipe after pulling the outer plastic off of it
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post #7 of 16 Old 10-29-2013, 08:41 AM - Thread Starter
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Which of the 2 rigid foam?
see pics:

the pink seems to be R40 , whereas the Dow is R8

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post #8 of 16 Old 10-29-2013, 09:01 AM
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Quote:
Originally Posted by cgott42 View Post

Which of the 2 rigid foam?
see pics:

the pink seems to be R40 , whereas the Dow is R8


That pink is R4 not R40. I used that 3/4" pink foam board myself on all foundation walls and the floor.
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post #9 of 16 Old 10-29-2013, 11:43 AM - Thread Starter
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Does the 3/4" Pink board - also serve as a vapor barrier?
Also - how do you attach it to the foundation wall?

Also - Anything cheaper than this?

Would need approx. 50 linear feet - @ $6.5 linear foot = $325!
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post #10 of 16 Old 10-29-2013, 12:15 PM
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Quote:
Originally Posted by cgott42 View Post

Does the 3/4" Pink board - also serve as a vapor barrier?
Also - how do you attach it to the foundation wall?

Also - Anything cheaper than this?

Would need approx. 50 linear feet - @ $6.5 linear foot = $325!

Yes. I used PL300 to attach it to the walls and floor.

What kind of area are you looking to cover? The stuff you referenced is odd shaped and not standard (thus the higher cost). I would use this if you want 1 1/2" thick. I used the 3/4" tongue and groove (cheaper but slightly smaller R value) with the PL300 and some house wrap tape and ended up with pretty good results.

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post #11 of 16 Old 10-29-2013, 01:38 PM - Thread Starter
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thanks - that's $5.5 lin. ft = $275 ($50 cheaper is cool)
Unfortunately they don't sell it in my home depot.
Anything similar @ Lowes?
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post #12 of 16 Old 10-29-2013, 06:33 PM
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Quote:
Originally Posted by cgott42 View Post

thanks - that's $5.5 lin. ft = $275 ($50 cheaper is cool)
Unfortunately they don't sell it in my home depot.
Anything similar @ Lowes?

So they don't sell the 1 1/2"? Looks like Lowes only has 1" in your area. Any construction supply retailers in your area?
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post #13 of 16 Old 10-30-2013, 11:47 AM
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Quote:
Originally Posted by cgott42 View Post

Since the back of the wall is open , what holds the unbacked insulation that's in the study wall in place?
Also - being that I already have standard R13 paper backed - is that a problem ?
i.e. how much of a problem is it? Also (for my own knowledge)- what is the reason that the 2nd paper / vapor barrier is a problem, and not added benefit?

thx

You can push the fiberglass back so it touches the foam board - that will not short circuit the decoupling because the fiberglass is not rigid.

2 vapor barriers traps moisture in between - not good. If you already have it, at least slash some cuts in the paper after installation so it no longer acts as a vapor barrier.

By the way, you should use minimum of 1.5" of rigid foam - if you only use 3/4" then you no longer have a vapor barrier (foam must be at least 1.5" to be considered a vapor barrier). 2" foam + fiberglass is well studied so is advisable.
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post #14 of 16 Old 10-30-2013, 12:36 PM
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Quote:
Originally Posted by kromkamp View Post

2 vapor barriers traps moisture in between - not good. If you already have it, at least slash some cuts in the paper after installation so it no longer acts as a vapor barrier.

By the way, you should use minimum of 1.5" of rigid foam - if you only use 3/4" then you no longer have a vapor barrier (foam must be at least 1.5" to be considered a vapor barrier). 2" foam + fiberglass is well studied so is advisable.

+1 on both of these comments. If you have the stuff with kraft paper facing, just put plenty of slices in it with a blade. Also, pick up a hammer tacker like THIS ONE. It's a cheap and easy way to get the insulation to stay in place.

You're located in NY...I would check local code, but I bet your required R value for basement walls is R11. (I'm in Albany and that's what my inspector told me for this area.) More importantly, and as kromkamp states above, I also read somewhere that 1" XPS does not qualify as a vapor barrier. In my opinion, the extra ~$200 now is very much worth it...

Finally, be sure you address the rim joists/sill areas. Homes lose a lot of heat in this area and it will be well worth your time to seal it up well. I would cut the 2" foam to the approximate size and then fill in any gaps with Great Stuff...an excellent product for getting into those small gaps (available in cans at HD for ~$5).

The Esquire Theater Construction Thread:
http://www.avsforum.com/avs-vb/showthread.php?t=1289590
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post #15 of 16 Old 11-11-2013, 08:56 PM - Thread Starter
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thanks - so I'll get this 2" foam

Says it's R-10

Q - On one wall I currently have wallpaper directly glued to the foundation wall - do I need to remove the wall paper before I put this on (not a pleasant job to do)?
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post #16 of 16 Old 02-28-2014, 04:55 PM
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I'm starting a similar project. Existing basement walls have studs against concrete and drywall....no insulation. Tearing it down.

 

You do not want food for mold on the walls or floor of a basement. Period. No wood, no paper. I'm not sure if mold spores would be behind the 2" foam you adhere to walls. But wallpaper and moisture are ingredients enough for mold. Would it smell behind the foam? Not sure, but since it's wallpaper on concrete, I'm sure you could be more aggressive physically or chemically about getting the wallpaper down.

 

And you need to ****** the movement of water from the concrete that's sitting in moist soil. And you need to keep the moisture of air in basement from condensing on cold 50 deg concrete walls. Fluffy insulation doesn't do that, so while one sees it in a lot of [older] basements, we know now not to do that. 

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