# Thoughts on this insulation placement



## info2x (Aug 19, 2012)

Well I've been working on my bathroom and came across something I didn't quite expect. I found insulation on an interior wall (yellow hashed area in drawing below). That doesn't strike me as that odd since the wall borders the open stairwell to below so perhaps it's for noise abatement. What struck me as odd was the vapor retarder. 



Was curious as to everyone's thoughts on if the when I go to put the insulation back for soundproofing if I should keep the vapor retarder. I know that typically interior walls don't need them, but is there any harm?











For what it's worth the insulation that is below the subfloor doesn't seem to have a vapor retarder and not all of the interior walls had insulation in them.


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## SeniorSitizen (Sep 10, 2012)

Lets hope it's just there for very slight noise reduction being it was installed wrong for insulating / vapor barrier purposes.


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## SPS-1 (Oct 21, 2008)

Must be for noise reduction. Normally, I would not think a vapor barrier on an interior wall would have any effect one way or another. However, that is a bathroom. I don't think I would want my bathroom wrapped with a vapor barrier.


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## PD_Lape (Nov 19, 2014)

SPS-1 said:


> Must be for noise reduction. Normally, I would not think a vapor barrier on an interior wall would have any effect one way or another. However, that is a bathroom. I don't think I would want my bathroom wrapped with a vapor barrier.


I thought it was a good to have a vapor barriers on bathrooms especially those surrounding the shower and the tub. Would you mind educating us (or just me)?


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## SPS-1 (Oct 21, 2008)

Without the vapor barrier, any moisture (from high humidity or other) behind the wall has the ability to dry towards the other rooms.


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## HomeSealed (Jan 3, 2008)

Did that staircase previously lead to an unconditioned attic perhaps?


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## PD_Lape (Nov 19, 2014)

SPS-1 said:


> Without the vapor barrier, any moisture (from high humidity or other) behind the wall has the ability to dry towards the other rooms.


So it wrapping the bathroom with vapor barrier would be harmful for the other interior walls in the long run?


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## info2x (Aug 19, 2012)

SPS-1 said:


> Without the vapor barrier, any moisture (from high humidity or other) behind the wall has the ability to dry towards the other rooms.


Well wouldn't it still have that ability? 

Inside air | Drywall | FG | VR| Drywall

As I understand it the VR/VB is there to prevent water vapor from entering the wall where it might condense. Since this is an interior wall and there isn't a huge temp delta across the wall the chances of condensation should be minimal. Or am I way off here?



HomeSealed said:


> Did that staircase previously lead to an unconditioned attic perhaps?


Nope. Staircase was part of the original floor plan. My guess is either they had this left over or whoever did the insulation work thought it might have been an exterior wall.


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## nap (Dec 4, 2007)

sound. Nobody wants to hear what you are doing in the bathroom.


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## Gary in WA (Mar 11, 2009)

"As I understand it the VR/VB is there to prevent water vapor from entering the wall where it might condense. Since this is an interior wall and there isn't a huge temp delta across the wall the chances of condensation should be minimal. Or am I way off here?"------- Exactly, as I understand it also. Diffusion is really slow without air pressure/temps differences relying only on wicking after wet- unlike an exterior wall. 

The paper facing is .3-1 perm (dry cup), opening up (hygroscopic) the wetter it gets (5-10 perms); http://www.certainteed.com/resources/3028097.pdf

Depending on the manufacturer; http://www.buildingscience.com/documents/insights/bsi-024-vocabulary

Use an oil base paint or vapor barrier paint if you want to contain the moisture to the bath and a good fan w. timer/humidistat. 

Gary


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## ddawg16 (Aug 15, 2011)

PD_Lape said:


> So it wrapping the bathroom with vapor barrier would be harmful for the other interior walls in the long run?


If the vapor barrier is an issue in this case, then you have bigger problems. The moisture in the bathroom should not be getting through the walls. That is one of the reasons for using a semi-gloss paint.....and proper ventilation.



nap said:


> sound. Nobody wants to hear what you are doing in the bathroom.


In my case, the noise is the least of your worries. 


If I had to speculate in this case....the reason for the paper is.......because, that is what he had laying around. I'm willing to bet that the installer has intentions of trying to control vapor....just noise.


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## gregzoll (Dec 25, 2006)

Another vote on cheap noise reduction. If you wish, you can pull it out, if you are not worried about noise. I would be more apt to sound insulate a bedroom that may butt up against a common space (ie Kitchen, Living Room, Home Theater/Entertainment space), than the bath.


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## info2x (Aug 19, 2012)

ddawg16 said:


> If the vapor barrier is an issue in this case, then you have bigger problems. The moisture in the bathroom should not be getting through the walls. That is one of the reasons for using a semi-gloss paint.....and proper ventilation.
> 
> 
> 
> ...


I agree. Fortuneatly it isn't an issue it just caught me off gaurd and I wanted to make sure there wasn't some side note that I had missed about VR on bath walls.



Gary in WA said:


> "As I understand it the VR/VB is there to prevent water vapor from entering the wall where it might condense. Since this is an interior wall and there isn't a huge temp delta across the wall the chances of condensation should be minimal. Or am I way off here?"------- Exactly, as I understand it also. Diffusion is really slow without air pressure/temps differences relying only on wicking after wet- unlike an exterior wall.
> 
> The paper facing is .3-1 perm (dry cup), opening up (hygroscopic) the wetter it gets (5-10 perms); http://www.certainteed.com/resources/3028097.pdf
> 
> ...


Agree. Plan is to put a better bath vent in there now. Current vent centered in the lower cross part of the T because directly outside of the shower is a sky light. I was thinking a remote vent with two inlets might be a good solution.

I'll draw a better picture later.



gregzoll said:


> Another vote on cheap noise reduction. If you wish, you can pull it out, if you are not worried about noise. I would be more apt to sound insulate a bedroom that may butt up against a common space (ie Kitchen, Living Room, Home Theater/Entertainment space), than the bath.


The wall in question is open to downstairs, the other side of the bathroom borders a bedroom. I'm not sure I would put insulation behind the bathtub so this is probably a decent compromise at isolating the upstairs from a noise perspective.


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## gregzoll (Dec 25, 2006)

Water noise when filling the tub, or while taking a shower. You can decouple the wall in the Bedroom, by using clips & two layers of Drywall with Green Glue between.


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## info2x (Aug 19, 2012)

As promised.



Vent is in front of toilet centered in the opening. Skylight is centered to the tub. Tub is left hand drain.



gregzoll said:


> Water noise when filling the tub, or while taking a shower. You can decouple the wall in the Bedroom, by using clips & two layers of Drywall with Green Glue between.


I could, but I'm not about to do that for a guest room. :no:


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