[91BlckGT]

Hi,


Quick question before I progress farther. I have about 20 sheets of R-30 insulation to stuff in the ceiling, soffits.


My plan is to have it vapor barrier down in the ceiling joists over the soffits, and then vapor barrier where the fiberglass will actually touch the drywall, to keep it from "buzzing", and to maximize the trapping.


Is this sound acoustical theory, or does it not matter in the slightest which way I face the vapor barrier? All things equal, I'd rather have the vapor barrier down, so I'm not breathing fiberglass flakes as I work on the theater.

Here's a pic where I tried it both ways. I can trim off the vapor barrier.

Oh, and if I have a 1/4" gap between the fiberglass and joists, or gaps in the fiberglass, how bad is this? With two layers of 5/8" DD, I figure the only thing making it to the drywall is low-bass energy, so even if there are some air gaps, the reflection of the waves around will still be sucked up by 9" of the fluffy stuff.


Thoughts?

 

[SteveMo]

There is any number of things floating around in all the air we breath. There is fiberglass floating around outside in the air.


The gap is used to improve the effectiveness of the energy savings in your home. The vapor barrier is code to any exterior wall and that would be with the fluffy side to the inside of the room and kraft paper to the exterior.


Consider wearing a mask, eye protection, and do not I repeat, do not sit on the nice sofa before a change of clothes. Then you could use a vacuum with a hepa filter included or whatever kind woln't just blow the stuff around and suck up all the excess particles. Allow it to settle then repeat that if you need to.


Don't worry about the 1/4" gap, but I would remove the paper if there is another room above. I don't understand how you say the fiberglass will touch the wall also then buzz. There are many considerations which concern acoustics but that do not always apply to what applications we use or forseen problems worth concentrating on, and I think buzzing fiberglass would fall into this category.

 

[James Mos]

I live in New Jersey and the inspectors actually wanted the vapor barrior sliced when I installed it in the basement ceiling. I think the vapor barrior is only to be kept in-tact when on exterior walls.


I just installed it all with the barrier down(facing basement floor), and then I went back around with my utility knife and just cut x's down the lengths of the paper.


Best bet is to check with your local inspectors to see what they require.

 

[In2Photos]



Quote:
Originally Posted by SteveMo /forum/post/15437132


The vapor barrier is code to any exterior wall and that would be with the fluffy side to the inside of the room and kraft paper to the exterior.

I don't think so. Faced insulation should be installed with the paper on the INSIDE wall.


In this case the paper isn't really a vapor barrier. I would leave it out completely unless it provides some other benefit.

 

[SteveMo]



Quote:
Originally Posted by In2Photos /forum/post/15437676


I don't think so. Faced insulation should be installed with the paper on the INSIDE wall.


In this case the paper isn't really a vapor barrier. I would leave it out completely unless it provides some other benefit.

The paper will decrease the NRC. Since they have foam on the wall and they are installing faced insulation in what appears to be a lower floor I would think maybe they could not get unfaced R19 in the economy size also. I tried to get unfaced and they would no longer carry this at one of the hardware stores and I was thinking this could be what the OP has done. If this is the case it would be better to place it with facing onto the foam.



I think I was thinking that insulation is code.

 

[Ted White]

We're not measuring NRC of insulation once it's in the cavity, however. The free-air measurement isn't appropriate.


Personally I love the paper face for the practicality of attachment.


The small air gaps are meaningless from an isolation / absorption perspective. Having a ceiling cavity 1/2 full of insulation is fine, and certainly much better than a stuffed cavity which can conduct and couple our assemblies.

 

[crunchyfrogs]

For the ceiling I put the vapor barrier on top. Reason being the old insulation I removed in a few spots...what little this old home had, was filthy. Covered in dirt and dust from the floor above. The vapor barrier will at least keep the dirt from above getting into the insulation. If the space above is conditioned I think this is ok.

 

[91BlckGT]



Quote:
Originally Posted by SteveMo /forum/post/15437867


The paper will decrease the NRC. Since they have foam on the wall and they are installing faced insulation in what appears to be a lower floor I would think maybe they could not get unfaced R19 in the economy size also. I tried to get unfaced and they would no longer carry this at one of the hardware stores and I was thinking this could be what the OP has done. If this is the case it would be better to place it with facing onto the foam.



I think I was thinking that insulation is code.

Excellent guess! This is in the basement. The "REAL" vapor barrier is the R3 styrofoam that is glued, nailed, and then caulked onto the framing. I'm not the slightest bit worried about the vapor barrier at all, nor am I worried about code. The code just requires 60% insulation coverage on the wall, which I have.


And yes, i bought faced because it was $5 cheaper a bag as the unfaced for the exact same length and quantity. That's silly to me, but that's how HD priced it.

 

[91BlckGT]



Quote:
Originally Posted by Ted White /forum/post/15438298


We're not measuring NRC of insulation once it's in the cavity, however. The free-air measurement isn't appropriate.


Personally I love the paper face for the practicality of attachment.


The small air gaps are meaningless from an isolation / absorption perspective. Having a ceiling cavity 1/2 full of insulation is fine, and certainly much better than a stuffed cavity which can conduct and couple our assemblies.

Regarding the stuffed cavity, there is a 1" space between the old joist and new joist in one area, and 1.5" in all the other areas. I was planning on sliding 3" thick R-10 insulation into these cracks, but it sounds like that would end up with a stuffed cavity.


When I did put fiberglass in there, it was packed tightly. Sounds like I should pull it out.


Thanks for the "half full" thing too. For the soffits that are 18" wide I was putting a single sheet of R-30 in it, but it sounds like that's not needed. I just didn't want a big reverberating cavity.

 

[Ted White]

Insulation is really in interesting thing.


It's intuitve that a great deal of sound isolation will come from using it- false. While it is definately something you want to use, it is not as impactful as decoupling, mass or damping. In a non-decoupled assembly, the improvement from using insulation is really quite minimal.


It's intuitive that an exotic "acoustic" insulation would really do more for a guy - false. Inumerable acoustic tests make it clear that the cheap stuff, regardless of color, works as well as anything.


It's intuitive that filling the cavity completely will be better than 1/2 full - false. Again, studies show that a 1/2 full ceiling cavity with R19 does not improve in practical terms compared to filling with R30.


It's intuitive that "increasing the density" of insulation should help even more - false. The fact is that you want a low density application of insulation in a cavity, and you certainly do not want to risk over-compressing and thereby conducting vibration.


It's intuitive to want to put a little insulation in all sorts of spots - false. Because the air cavity behind a double stud wall or decoupled ceiling is really just one big air cavity, it's an additive thing. The systems absorption is defined by the sum of all the insulation (to a large degree) not a section by section assessment.


Anyway, I have found this interesting over the years.