John Sayers' Recording Studio Design Forum

Initially when the building framing was constructed, there was a layer of 6 mil poly put on for vapour barrier on the inside of the 2x6 studs of the outer(outside walls)
Since i will be finishing the wall with an inner leaf (2x4-DW on inner side, open on back), and the VP rule is that it should be no more than 1/3rd the distance from the inner wall surface(warm side), i have to slash the existing VP and put new stuff on closer to the warm side.
Calculation=
outer to inner wall:
-3/8" cement board
-5/8" ext drywall
-5.5" (2x6)
-2.5" Stapping for extra width (2x3 on end)
-1" air space-
-3.5" (2x4 inner wall)
-1.25" (2 layers 5/8th DW)
Total 14.75" wall thickness /3 =4.9"

VP is presently at 8.25"s in from interior face and needs to be at 4.9" or less

see pic below.

So my question is:I have read that in some instances, pink insulation with paper backing can perform differently than non backed batts.... is this 6 mill poly remaining in the cavity after i slash it going to be a factor in my STL?
Should i remove as much as possible or just break the seal?
I have a significant amount do deal with unfortunately.
thanks

Seaweed.

There is no one, no where, well, 2 things, that says "VP" or that ASSUMES from listening to their brother in law that a vapor barrier sits in a 1/3 part of a wall.

In your area of the world...it goes, this what you call VP, what others call a vapor barrier and what I refer to as a Vapor Diffuser Retarder, goes on the interior side of the interior framing.

Magic gone.

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Brien Holcombe
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Sound: You can't stop it, you can only try to contain it.

I used VP to mean vapor barrier, not sure why, guess i should have said VB. Anyway, semantics, but that said, i do not understand the rest of your post, could you say it differently somehow?

The 1/3 rule is well known and in use here, perhaps it is a climate thing, but it is well regarded all the same.

But i asked more about leaving the poly in there and it's affect on the isolation, any comments on that?

BTW i didn't say it SHOULD sit 1/3 of the way in i said that was the maximum suggested distance from the warm side.

Well known and wrong.

To suspect that there is a mathematical equation that can account for this environmental phenomenon...is hard headed at best...and dismisses Science at worst.

Here is the thing...Moisture moves from the warm side to the cold side. The warm side is, in your neck of the woods, the interior of the dwelling. So when it moves from this warm side to the cold side...what does it encounter?

In your scenario, it hits the barrier somewhere in the middle of the double wall assembly.


In a double wall assembly you will have insulation on both sides of the frames...meaning, you essentially have a potential sponge on the inside of the wall and the "wetting" that happens as a direct result of condensation creates a mold issue that you do not know about for some time.

Even if it were a simple exterior home wall...the vapor diffusior retarder goes where? You tell me where this 1/3 area is in a simple framed wall...

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Brien Holcombe
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Sound: You can't stop it, you can only try to contain it.

You are clear that my position is that i am moving the vapor barrier to just under the drywall on the warm side of the wall right?

My question actually has to do with whether the old (wrong vapor barrier, old VB, not in the right spot vapor barrier) once slashed will be a problem regarding STL. The material, the plastic in the wall along with the insulation as opposed to just pink fiberglass.
Do you have any thoughts on that?

I think I'd try to get the old stuff out as much as possible, if I were you. Probably not a big deal, but you don't really know what it might be doing, acoustically.

- Stuart -

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I want this studio to amaze people. "That'll do" doesn't amaze people.

Right, makes sense. Thanks for confirming that. I don't mind working i just hate working for no reason on stuff.

It's a hugh deal Stuart, it is what is called a double barrier. Indeed the vapor barrier...one and only one, go's in the place that it goes, depending on where in the world you live. UP North, it is on the interior,,below the equator, in hot areas...goes on the outside of the assembly.

So to have two, let's explore what that does. Well, the condensation from the inside is extracted by the HVAC. The exterior wall assembly, as it condenses, maybe it gets dried to the outside..maybe not.

But what about the area between the two barriers? This becomes a trap. There is no air that does not have moisture...H2O right? So when it attempts to find a path of egress it hits a barrier in either direction, the recipe for rot.

Know what you are talking about before you say something that someone might think is truth.

We fight against that type of thinking every day around here.

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Brien Holcombe
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Sound: You can't stop it, you can only try to contain it.

Not really: The OP was saying that he has slashed huge cuts all over the original barrier, which pretty much wrecks its properties for preventing the passage of vapor. The way I read his post, he's worried if he needs to take out the dangling pieces of slashed old vapor barrier, or if he can leave them in place. As a vapor barrier, not really an issue. But who knows what it might be doing, acoustically? That's the gist of my comment: Might not be a biggie, but I'd take it out anyway, since that type of construction has never been tested in an acoustic lab, as far as I'm aware. I don't think he wants to be a guinea pig in testing new acoustic designs based on "slashed vapor barrier"!


- Stuart -

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I want this studio to amaze people. "That'll do" doesn't amaze people.

Sorry, I thought your comment "not a big deal" might have suggested that the original VDR could stay with no ramifications.

I would suggest cutting it out completly, since the remaining pieces could "flap" around in the cavity.

_________________
Brien Holcombe
_____________________________________________
Sound: You can't stop it, you can only try to contain it.

Yup! That's my thinking too.

You know the old saying: "Great minds think alike!"


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Cool. This is very useful discussion regarding Vapor barrier, thanks guys.