Where to put faced insulation?

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howiedrum
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Location: Arcata, California USA

Where to put faced insulation?

Post by howiedrum »

I am nearing the insulation phase of my studio build. All the insulation has been purchased and is on site. The original plan was to fill the 2x6 cavities with faced R-19 fiberglass insulation and then fill the inner leaf 2x4 wall cavities with sound installation (safe n sound mineral wool), which is unfaced.

My question is if I do this, then the vapor barrier (faced side of R-19) ends up in the middle of the whole wall assembly, which I have read is not good. Typically, I learned that vapor barriers or retarders should be placed inside the cavity up against the surface that is warmest in winter. For me that would be up against the inner leaf OSB/Drywall sheathing. Also, I read that OSB also acts as a vapor retarder when used as interior sheathing. So if I go as planned, would I have two vapor retarders inside the wall? The faced R-19 in the middle and the OSB on the inner leaf?

My current thought is to switch the order and put the safe n sound mineral wool in the 2x6 bay cavity and then add the R-19 faced insulation so the vapor barrier in its proper place up against the inner leaf OSB sheathing.

I look forward to hearing your opinions.

Thank you and I hope all is well during this pandemic.
Gregwor
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Re: Where to put faced insulation?

Post by Gregwor »

How big is your gap between your inner and outer leaf framing? The 2x6 insulation will be 5.5" thick which will be fine if your gap is 2". Any smaller and the insulation will compress and that is not good. I do agree that you should put the facing up against your inner leaf sheathing.

Greg
It appears that you've made the mistake most people do. You started building without consulting this forum.
howiedrum
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Joined: Thu May 25, 2017 8:09 am
Location: Arcata, California USA

Re: Where to put faced insulation?

Post by howiedrum »

How big is your gap between your inner and outer leaf framing?
I have a one inch gap. It goes 2x6-1" gap - 2x4. So I have 5.5 + 1 + 3.5 = 10 inches in total. The R19 is 6.25" thick and the Safe n Sound is 3" thick. So I am not worried about compression because I am only adding 9.25" of insulation.
I do agree that you should put the facing up against your inner leaf sheathing.
This was my main question. Good to know you agree that the facing should go up against the inner leaf sheathing.

Thanks Greg I appreciate it.
Gregwor
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Re: Where to put faced insulation?

Post by Gregwor »

I have a one inch gap. It goes 2x6-1" gap - 2x4. So I have 5.5 + 1 + 3.5 = 10 inches in total. The R19 is 6.25" thick and the Safe n Sound is 3" thick. So I am not worried about compression because I am only adding 9.25" of insulation.
Yes, but if you put the 6.25" insulation in your inner leaf 2x4 frame, the frame plus the 1" gap only equals 4.5" of space to squeeze in 6.25" of insulation. Therefore, every spot that there is a stud, the insulation will be super compressed :|

Greg
It appears that you've made the mistake most people do. You started building without consulting this forum.
howiedrum
Posts: 36
Joined: Thu May 25, 2017 8:09 am
Location: Arcata, California USA

Re: Where to put faced insulation?

Post by howiedrum »

Yes, but if you put the 6.25" insulation in your inner leaf 2x4 frame, the frame plus the 1" gap only equals 4.5" of space to squeeze in 6.25" of insulation. Therefore, every spot that there is a stud, the insulation will be super compressed :|
The extra inches would just go into the 2x6 cavity. Am I missing something? Here is a photo of my wall. /Users/howiedrum/Desktop/Double stud wall.jpg
Gregwor
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Re: Where to put faced insulation?

Post by Gregwor »

Your inner studs should have been staggered against the outer leaf studs in order to obtain the maximum distance between your inner and outer leaf sheathing. Right now, you only have 1" between your studs. In some spots that unavoidable, but not good to have throughout your entire build! Furthermore, if you do put the insulation like you intend, there will be NONE in between the studs, further increasing the resonant frequency and trashing your isolation even further. If I were you, I would knock those studs out and even toenail them in in different locations. However, then you're having to deal with the insulation issue I mentioned above. Maybe I'm blowing this out of proportion here but it's very concerning in my mind. Does anyone else have opinions on this?

Greg
It appears that you've made the mistake most people do. You started building without consulting this forum.
howiedrum
Posts: 36
Joined: Thu May 25, 2017 8:09 am
Location: Arcata, California USA

Re: Where to put faced insulation?

Post by howiedrum »

Your inner studs should have been staggered against the outer leaf studs in order to obtain the maximum distance between your inner and outer leaf sheathing.
Why? I don't understand. This is a double stud wall. Two separate leafs. Two separate plates. How would staggering the studs change the distance between my inner and outer leaf sheathing?

Below is an example I have followed:
Double Stud Wall.png
Paulus87
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Re: Where to put faced insulation?

Post by Paulus87 »

howiedrum wrote:
Your inner studs should have been staggered against the outer leaf studs in order to obtain the maximum distance between your inner and outer leaf sheathing.
Why? I don't understand. This is a double stud wall. Two separate leafs. Two separate plates. How would staggering the studs change the distance between my inner and outer leaf sheathing?

Below is an example I have followed:
Double Stud Wall.png

I believe the reason for why staggering the studs between the two walls is preferable is because it helps to break up the low frequency waves a little more than when the studs are aligned. Much like waveguide absorbers. I don't think it's a massive deal though, just a little extra kick.

I also do not see how it increases the overall distance between the two sheathing layers. Yes, there is a 1" gap between the studs when they are facing opposite each other, when they are staggered then that 1" gap disappears, is that what you mean Greg? but it doesn't increase the distance between the sheathing.

Paul
Paul
howiedrum
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Re: Where to put faced insulation?

Post by howiedrum »

I believe the reason for why staggering the studs between the two walls is preferable is because it helps to break up the low frequency waves a little more than when the studs are aligned. Much like waveguide absorbers. I don't think it's a massive deal though, just a little extra kick.
Thanks Paul. That is a relief. After two years studying and reading about double stud walls I am bummed I didn't realize this.

One more piece of advice. Inside my middle leaf ceiling joists the builders put faced insulation. Below that is an 18" gap where my silencer boxes and ducts are suspended. Below that is a layer of 5/8drywall and 3/4 OSB on top of my inner leaf joists (inside out ceiling). See photo.
IMG_4610.jpg
I still need to add insulation between my inner leaf joists. The builder bought more faced insulation for this. If installed face down towards the room (later covered with fabric), do you think this constitutes as two vapor barriers in my ceiling? The facings would be approximately 28 inches apart. Should I remove the facing of the insulation above the silencer boxes or should I remove the facing prior to installing in my inside-out ceiling? Or is having them both faced not problematic. Here is another picture showing the inner and middle leaf ceilings.
IMG_4611.jpg
Thank you.
Paulus87
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Location: Wales, UK

Re: Where to put faced insulation?

Post by Paulus87 »

howiedrum wrote:
I believe the reason for why staggering the studs between the two walls is preferable is because it helps to break up the low frequency waves a little more than when the studs are aligned. Much like waveguide absorbers. I don't think it's a massive deal though, just a little extra kick.
Thanks Paul. That is a relief. After two years studying and reading about double stud walls I am bummed I didn't realize this.

One more piece of advice. Inside my middle leaf ceiling joists the builders put faced insulation. Below that is an 18" gap where my silencer boxes and ducts are suspended. Below that is a layer of 5/8drywall and 3/4 OSB on top of my inner leaf joists (inside out ceiling). See photo.
IMG_4610.jpg
I still need to add insulation between my inner leaf joists. The builder bought more faced insulation for this. If installed face down towards the room (later covered with fabric), do you think this constitutes as two vapor barriers in my ceiling? The facings would be approximately 28 inches apart. Should I remove the facing of the insulation above the silencer boxes or should I remove the facing prior to installing in my inside-out ceiling? Or is having them both faced not problematic. Here is another picture showing the inner and middle leaf ceilings.
IMG_4611.jpg
Thank you.
In a two leaf system, the vapour barrier should go on the warm side of the cavity insulation (behind your inner leaf drywall). I am guessing since you have a vented roof the vapour barrier should go behind the middle leaf drywall, since the idea is to stop warm moist air leakage to your roof deck, which helps your vents do their job preventing condensation forming on the bottom of your roof deck. But having just dealt with a condensation nightmare myself in my own studio I would double check this until you're 100% certain what you should do.

1. I personally don't know if the facing on insulation is a very good vapour barrier since it is easy to have holes/gaps/breaches which makes the vapour barrier useless since it should be a continuous unbroken barrier preventing as much moist air leakage as possible.

2. The cavity should be fully filled as much as possible.

3. I do not know whether it matters from a moisture point of view if the paper facing is left on your acoustic insulation inside your inside out ceiling modules...from an acoustics point of view it will reflect some highs and high mids back into your space, which may or may not be desirable depending on your acoustic design concept.

Paul
Paul
howiedrum
Posts: 36
Joined: Thu May 25, 2017 8:09 am
Location: Arcata, California USA

Re: Where to put faced insulation?

Post by howiedrum »

In a two leaf system, the vapour barrier should go on the warm side of the cavity insulation (behind your inner leaf drywall). I am guessing since you have a vented roof the vapour barrier should go behind the middle leaf drywall, since the idea is to stop warm moist air leakage to your roof deck, which helps your vents do their job preventing condensation forming on the bottom of your roof deck. But having just dealt with a condensation nightmare myself in my own studio I would double check this until you're 100% certain what you should do.
The building inspector just left and he said we didn't need any insulation in the vented attic and that the faced insulation in the middle leaf joists was fine in regards to moisture. He was concerned about the potential that the facing could catch on fire. His solution was to put rock wool high up in the 1" gap under the two ceilings to form a fire block. So we can leave the facing on, which was a huge relief to my builders. He also suggested to use non-faced insulation for the rest of the building. So we are going to try to take back all of the faced fiberglass insulation and buy unfaced. If we can't return the faced batts, then we will just cut the paper off the insulation we have before installing.

I am relieved to put the whole faced insulation questions to bed.

Thanks for your help!
howiedrum
Posts: 36
Joined: Thu May 25, 2017 8:09 am
Location: Arcata, California USA

Re: Where to put faced insulation?

Post by howiedrum »

Do you have any product recommendations for a tight-weave mesh I can use to cover the insulation in my inside-out ceiling?

I was curious if anyone has ever used Tyvek house wrap? It is strong, available, cheap, and I believe it would protect me from loose fibers from filtering down into my studio. I would cover it with fabric so it wouldn't be seen.

Thanks,

Howie
Paulus87
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Re: Where to put faced insulation?

Post by Paulus87 »

You could use a thin (12mm) polyester wadding or Dacron, that will keep the fibres out and provide a little extra absorption. It also provides a nicer finish since it rounds the edges of the timber slightly.

You can even get the thicker version of the stuff and just use that as your acoustic treatment, it has a gas flow resistivity of about 3000rayls so is perfect for thick bass trapping.

Other options include a thin plastic which will have a slight membrane effect while reflecting some highs back in the space, or you could use an upholsterers mesh.

Paul
Paul
howiedrum
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Joined: Thu May 25, 2017 8:09 am
Location: Arcata, California USA

Re: Where to put faced insulation?

Post by howiedrum »

Do you have any links or photo's of the polyester wadding or Dacron you were mentioning. I have been looking online but I am still a little unclear.

Thank you,

Howie
howiedrum
Posts: 36
Joined: Thu May 25, 2017 8:09 am
Location: Arcata, California USA

Re: Where to put faced insulation?

Post by howiedrum »

Would this be a good choice to cover the insulation in my inside-out ceiling?
IMG_4693.jpg
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