insulation interior wall without drywall, plastic sheet on the outside?

[masraum]

< edit > I should have proofread read the title before posting. I am sure a bunch of you are reading the title and wondering WTH I'm talking about. Hell, that's what I thought when I read it.< /edit >

We've added a wall back into the house that was removed years ago. We're hoping to cut the sound through the wall so we're going to add insulation (among other things like 2x6 wall with alternating 2x4 studs so the walls are decoupled plus 5/8 type X drywall).

I want to put the insulation in the wall, but we were thinking of having someone come hang and finish the drywall on the wall as well as mud/repair a bunch of other drywall in the house.

The problem is going to be making sure the insulation stays put. I'd wondered about putting plastic sheet on one side, then insulation, then more plastic sheet. The sheet would hold the insulation in place until the drywall can be hung. Since it's an inside wall, I don't think condensation would be much of an issue, or would it?

Any other reasons why it is a bad idea or any better ideas?

[Gogar]

Is this an exterior wall? If so then you absolutely need to put a plastic vapor barrier on the inside (warm) side of the wall.

If it's an interior wall I don't think you'll have problems doing whatever you want but I don't think you should really try to put plastic on both sides.

As far as sound deadening goes the insulation is nice but air movement is the big thing. A beautifully insulated wall with something as simple as leaky AC box cuts or even a round hole the size of a quarter will negate a big part of the sound deadening.

[masraum]

Originally Posted by Gogar

Is this an exterior wall? If so then you absolutely need to put a plastic vapor barrier on the inside (warm) side of the wall.

If it's an interior wall I don't think you'll have problems doing whatever you want but I don't think you should really try to put plastic on both sides.

As far as sound deadening goes the insulation is nice but air movement is the big thing. A beautifully insulated wall with something as simple as leaky AC box cuts or even a round hole the size of a quarter will negate a big part of the sound deadening.

Interior wall. The old house is like a sieve, but this wall is going to be tight. And the insulation is going to be mineral wool which does cut sound a fair amount. There will be an outlet on both sides, but both outlets will be sealed up (I've got some mass loaded vinyl and some aluminum tape). I know it's not going to be like a studio wall, but hopefully, it'll be better than your average home wall.

[Bill Douglas]

As Cougar said some plastic vapor barrier. It's waterproof (water resistant really). and won't get condesation as it can breath. Great stuff.

[Gogar]

Is Cougar my neighbor nickname?

[rockfan4]

When they built my house, code was that the basement walls had to be insulated. They put in loose bats, and put a thin fabric to hold the bats in place. So air could freely pass through it, but it held the insulation in place.

I built a exercise room in the basement, I ended up using a similar fabric. The ceiling is 3 1/2" of denim insulation, then a layer of sheet rock, then some metal isolation clips and then a second layer of drywall. On the walls I used the same denim insulation, and one layer of drywall on one side of the wall, and two on the other.

It's not 100% soundproof, but it's pretty good. Solid door as well, not a hollow one.

[masraum]

Thanks

[Bill Douglas]

Originally Posted by Gogar

Is Cougar my neighbor nickname?

Oh sorry.

Yes we all talk about you behind your back and call you Cougar.

[908/930]

How quiet are you trying to make the wall? You are on the right track with 2x6 with alternating studs and 5/8 drywall. I have some walls that I did that way and works very well. The mineral wool between will be a little bit of a problem because of the alternating studs, but worth the effort in my opinion, also good fire break. The batts cut tight will stay in place. Plastic sheet should be fine on a inside wall so you don't have fibres floating around. Remember the 5/8 type x has fiberglass strands running through it so cut with caution. I think there is a 5/8 without the glass strand available.

If you are trying to keep a room quiet the door will be harder to keep the noise from passing through, likely need a very heavy solid door.

[oldE]

On an interior wall I would not use plastic. To hold the insulation in place you could staple something like duct tape onto the studs if you are using Batts, or a breathing material such as tyvec if the insulation material is looser.

Best
Les

[id10t]

Originally Posted by Gogar

As far as sound deadening goes the insulation is nice but air movement is the big thing. A beautifully insulated wall with something as simple as leaky AC box cuts or even a round hole the size of a quarter will negate a big part of the sound deadening.

We have 2x6 exterior walls with insulation and "normal" 2x4 interiors with insulation. Normal ducts, wall plates, etc. you'd expect.

When there were accidents on our corner, we never heard 'em. The house another 100 yards past us would hear the crash and call the cops.

When bedroom doors are closed, you can't hear someone knocking on the front door (I've missed a few critical deliveries due to this).

Unless masraum is cutting window boxes in his walls, I think he'll get the quiet bits he wants.

[billybek]

Basement interior walls I install a vapour barrier under the floor plate and up both sides of the wall approximately 16" on either side.
If you are using mineral wool for the sound deadener, it will friction fit between the studs and will not slip or drop because of the density of the product.
I used Roxul Safe and Sound.

[look 171]

Two layers of drywall and insulation will do the trick. A layer of sound board will also help instead of two layers of drywall. How much sound are you trying to muffle out and what kind of sound? You snore that loud? No need for vapor barrier if its interior wall.

[masraum]

Originally Posted by 908/930

How quiet are you trying to make the wall? You are on the right track with 2x6 with alternating studs and 5/8 drywall. I have some walls that I did that way and works very well. The mineral wool between will be a little bit of a problem because of the alternating studs, but worth the effort in my opinion, also good fire break. The batts cut tight will stay in place. Plastic sheet should be fine on a inside wall so you don't have fibres floating around. Remember the 5/8 type x has fiberglass strands running through it so cut with caution. I think there is a 5/8 without the glass strand available.

If you are trying to keep a room quiet the door will be harder to keep the noise from passing through, likely need a very heavy solid door.

One room will have our TV, and the other room will be my office and possibly a guest bedroom if needed. We are not going for "sound proof" but we are going for "quiet", especially on the wall between the two rooms. We'd like to keep my voice and the TV from being loud in the opposite room. I'm thinking that the decoupled studs/drywall will make a pretty big difference. I think the mineral wool will help. I went with the 5/8 X type drywall. I think that's got to help. Most drywall these days seems to be 1/2" "lightweight" so that each sheet is about 35# per sheet. This stuff is 5/8" and closer to 70-75# per sheet. I think the extra mass will help, and it's a lot cheaper and easier to get than buying something like "quietrock". And the reviews of the 1/2" quietrock are pretty moderate. I think for the big results, you need multiple layers or to use the commercial style drywall that the quietrock people make, and that stuff is THICK and HEAVY. I think they make some stuff that's between 1" and 2" thick and $$$$ and hard to find.

Originally Posted by oldE

On an interior wall I would not use plastic. To hold the insulation in place you could staple something like duct tape onto the studs if you are using Batts, or a breathing material such as tyvec if the insulation material is looser.

Best
Les

OK, thanks. Not a bad idea.

Originally Posted by id10t

We have 2x6 exterior walls with insulation and "normal" 2x4 interiors with insulation. Normal ducts, wall plates, etc. you'd expect.

When there were accidents on our corner, we never heard 'em. The house another 100 yards past us would hear the crash and call the cops.

When bedroom doors are closed, you can't hear someone knocking on the front door (I've missed a few critical deliveries due to this).

Unless masraum is cutting window boxes in his walls, I think he'll get the quiet bits he wants.

I think so too. I'm not looking for something that'll pass as a sound booth, and in this house, I wouldn't get that unless we were willing to strip the inside to the studs and strip the exterior of the house to the studs too, and we are not planning to do that now.

Originally Posted by billybek

Basement interior walls I install a vapour barrier under the floor plate and up both sides of the wall approximately 16" on either side.
If you are using mineral wool for the sound deadener, it will friction fit between the studs and will not slip or drop because of the density of the product.
I used Roxul Safe and Sound.

We're using something similar, but it is also R21.
Because we have alternating studs, they are 24", but alternating, so really 12". The only mineral wool around here is for standard 16" spacing, so there's going to be a lot of cutting involved, and we'll be using odd sizes here and there, so it may not friction fit like it would normally.

Originally Posted by look 171

Two layers of drywall and insulation will do the trick. A layer of sound board will also help instead of two layers of drywall. How much sound are you trying to muffle out and what kind of sound? You snore that loud? No need for vapor barrier if its interior wall.

I'd originally considered multiple layers of drywall, but in stead we went with the decoupled studs. So around the perimeter of the wall (top, bottom, and sides) they will be coupled which isn't ideal. But all of the studs in the middle of the wall are 2x4 every other one is faced to the opposite sides of the wall. We're using the 5/8 type X drywall instead of 1/2" lightweight drywall, and the wall will have mineral wool. It was a pain to find it around here for 2x6 walls, but I found some at Lowes.

[Bob Kontak]

Originally Posted by masraum

and the wall will have mineral wool. It was a pain to find it around here for 2x6 walls, but I found some at Lowes.

Just talkin'. I performed an audit at Carborundum's refractory brick facility in Niagara Falls in the way back. They had a machine that made "Blown Insulation". Molten ceramic was poured and the poured stream was blasted with high pressure air and it turned it into fiber. The refractory fiber was made into blankets and some were not dissimilar to the mineral wool which I think may be made about the same way.

[masraum]

Originally Posted by Bob Kontak

Just talkin'. I performed an audit at Carborundum's refractory brick facility in Niagara Falls in the way back. They had a machine that made "Blown Insulation". Molten ceramic was poured and the poured stream was blasted with high pressure air and it turned it into fiber. The refractory fiber was made into blankets and some were not dissimilar to the mineral wool which I think may be made about the same way.

Very cool.

This lady is very into energy efficiency and has several videos online including this one that talks about how mineral wool is made. I think it's about 60-90 seconds long. I watched several videos a while back on insulation, and like mineral wool compared to fiberglass for several reasons, especially in our house because of some of it's peculiarities which are mostly due to it being built by a farmer 100 years ago.

[look 171]

Steve how much sound are you trying to block out? Mineral wool? Depending on the sound or the amount that needs to be blocked out, look into other walls in the room and work on those because sound will come through the other three walls. I think having insulation in there will do the trick, but if you take sound meters and equip, then there should be differences between the different types of insulation but for the most part, iI really don't think you will hear the differences.

[URY914]

You must also tie the new wall into the existing wall properly to avoid sound transfer. You can’t just butt the new wall against the existing wall. New wall has to intercept old wall so sound doesn’t travel around the new wall.

2 layers of drywall is better then one and a layer of durock and drywall is better still.

We’re building exam rooms in new doctors offices and we do staggered studs, rock wool, proper wall tie-in and two layers of 5/8 rock. We’ve also done durock and drywall.

[mjohnson]

While I've never been in an anechoic chamber - my old office was a SCIF-like thing (but for DOE/NNSA stuff) with I think three layers of drywall + loaded rubber walls and 2.5" solid doors with massive seals. If the HVAC went down it got so quiet my head would go crazy. Like "I can't do work, can only hear my heartbeat in my ears" quiet. Maybe there's a limit?

Though, in our southwestern stick-built shack from the 1960s - I could really appreciate some sound related upgrades. Even more as our quiet (for now) 9yo won't be 9 forever, if you know what I mean.

I like to follow Matt Risinger's tube. Yes he's got sponsors and sometimes seems to be a shill but he seems pretty straight and he focuses on "high performance building". He's got a lot of stuff on sound as well as other things, particularly airflow and heat management.

[masraum]

Originally Posted by look 171

Steve how much sound are you trying to block out? Mineral wool? Depending on the sound or the amount that needs to be blocked out, look into other walls in the room and work on those because sound will come through the other three walls. I think having insulation in there will do the trick, but if you take sound meters and equip, then there should be differences between the different types of insulation but for the most part, iI really don't think you will hear the differences.

I thought and planned very specifically on this. We want it to be "quieter". We're just hoping that TV and voice (I've got one of those voices that "carry") will be muffled through the wall between 2 rooms so that if I'm working in one room, having the TV on in the other doesn't sound like the TV is in the room with me.