# How much insulation in a soundproof room?



## Otto (May 18, 2006)

Hi there,

I'm working on "soundproofing" my basement so that I can play guitar and drums down there with some degree of the sound not getting out to the rest of the house.

My main methods of keeping things quiet are double drywall, green glue and a staggered wall. 

I'm using insulation in the ceiling joists. Initially, I've put in one layer of R-13. I was wondering if it will make much difference to sound levels going up throught the floor to put another layer of R-13. There's room and budget for it, but if it's not going to make much difference, I'm not going to waste time with it. It's just basic fiberglass insulation from Lowe's; nothing fancy.

Any opinions appreciated.

Thanks!


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## bpape (Sep 14, 2006)

Realistically, if you want the isolation to be as good on the ceiling as it is on the walls, you either need to:

- not connect the side walls to the joists above and use PAC DC-04 clips. 

In addition to the above:

- Add another set of joists between the existing ones that only sit on the walls so you have a staggered stud ceiling in effect.

- Use PAC RSIC-1 clips and hat channel.

In any case, you want the joist cavity above COMPLETELY filled with insulation. If it's 2x12's, you'll want more than even 2 layers of R13. The more the better but no need to compress it - just fill it. The additional layer of drywall and Green Glue is absolutely a help - especially for drums. Just have appropriate expectations without the ceiling isolation as I discussed above.

Bryan


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## Otto (May 18, 2006)

Hi Bryan,

This project was kept as simple as possible. The walls will remain concrete, so there's nothing connected to the joists. Well, the one wall that's separating the storage room from the rest of the basement is connected to the joists, but that's the way it is. I may have to address the concrete walls for their reflections, but they should not convey much sound.

I thought about using RSIC clips, but chose not to because of the cost and complication. 

Really, the whole thing is a compromise, but it will be a lot better than nothing. 

I will fill those joists, and all other possible spaces, with insulation. Fortunately, it's not that hard or expensive.


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## John Simpson (May 10, 2007)

Certainly bookmark this link Otto. Even has Australian insulation coefficients!

Bryan, I notice you said *not *to secure the side walls to the joists above... I'm a little nervous about doing this myself, as our room needs all the structural integrity it can get (it will have a considerable IB sub system). How do you stop wall flex if you build like that?


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## bpape (Sep 14, 2006)

The walls will be plenty stiff. The clips hold the tops tight but offer a shearing force form of isolation onto a rubber bushing. For the money spent, this offers a tremendous reduction in structural sound transmission.

The only thing you don't get with this setup is the walls becoming structural (holding the floor up) which you don't have now and don't need.

Bryan


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## MatrixDweller (Jul 24, 2007)

Using Rockwool instead of fiberglass will yield better results as it is a bit denser. Doubling up will not provide a realistic improvement. 

The best soundproofing is high mass to dead air space to insulation to high mass. Double 5/8th drywall (or 5/8 and 1/2) will deaden the sound a lot but the low frequency vibrations will transfer from the drywall to the joists and up through the floor. The green glue will help with that. 

You could also use the green glue on the face of the joist to help a bit. RISC clips and resilient channel are the best, but adds a lot of complexity and using 2x 5/8 drywall would add the risk of your ceiling falling down if not done properly.

Another thing you could do is to use a layer of mass loaded vinyl under the flooring above the basement and/or between the sheets of drywall. It's pretty expensive stuff but is the goto material for ultimate soundproofing.

Avoid recessed lights or any holes in the ceiling at all as well.


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## bpape (Sep 14, 2006)

I would have to disagree on the airspace. You have a resonance that's set up based on cavity depth and the mass of the layers on top and bottom of that space. Air instead of insulation gains you nothing except money saved. Added insulation will absorb more of the cavity resonance.

Yes - higher density mineral wool is a better solution inch for inch. If it came down to a full cavity of fluffy stuff or 4" of mineral wool in a 12" cavity, I'll take the fluffy stuff any day. 

Bryan


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## MatrixDweller (Jul 24, 2007)

Resonance is when the sound waves bounce around inside a cavity. A resonant frequency is one that fits into that cavity and when bounced around starts to vibrate the materials causing an amplified effect. You do want the sound waves to bounce around because every hit off of a surface reduces it's energy slightly. That's what insulation does also, makes the sound bounce around inside itself removing it's energy. If you add a layer of insulation inside the cavity you would probably abate any resonant properties.

You have probably heard that providing an inch or two of air space behind a bass trap improves it's absorption. That's because the wave takes a bounce off the wall and goes back through the absorber. Sound waves also change when they go through different materials (wood, air, water, drywall, etc). 

Rockboard is not horrendously expensive but it wouldn't be cheap if you were to stuff the entire ceiling cavity (10"?) with it you would end up paying more than $10 per running foot. In a 16x12 room that would amount to almost $1500 of Rockboard in the ceiling. You would be better to add a third layer of drywall or use mass loaded vinyl, both of which would be cheaper.


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## bpape (Sep 14, 2006)

You're confusing WHY a space behind an absorber against the wall works. It's not the air, it's the distance from the leading edge of the absorbtion to the boundary. If you'd ever measured this effect, you'd find that 4" of absorbtion on a wall will do a better job than 2" with a 2" air gap.

The point of eliminating a resonance in the ceiling as soon as possible is to prevent it from building on itself and propogating to the floor (membrane) above. The mass below restricts the frequencies that can enter but EVERY cavity has a resonance that needs to be tamed. 

Trust me, I design rooms for a living. I've done this hundreds of times and measured the differences in the adjoining floor. I'll still take a full cavity of something half as dense any day.

Bryan


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## Mike P. (Apr 6, 2007)

Otto,
I originally used R-20 fiberglass insulation in my floor joists for an attempt at sound proofing. I added a second layer for a total of R-40. I also used plastic vapor barrier overtop of the insulation. The second layer made a difference. At "stupid levels" the only sound coming through is the low end bass, but that's unavoidable. I should mention I finished off the basement with a suspended ceiling made of compressed fibreglass panels. I imagine that helped too.


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## Otto (May 18, 2006)

Hi guys,

Interesting comments from all! An update from my end -- My basement is mostly finished. I ended up with two layers of plastic batted R-13 in the ceiling joists. That was a fairly tight fit, but without compressing much of the fiberglass. It was close enough to the edge of the joist that it wouldn't just sit in there; I had to staple it to keep it from falling out (unlike the first layer). I should have just gone for an R-30 or whatever right off the bat, but for some reason, I decided that it would be more fun to do the install twice. Not sure why I did that.

Aside from that, I did go with the staggered wall (using 2x6 framing) around the furnace/water heater/storage room. I then did double drywall and green glue all the way around. All lights are mounted on conduit on the outside walls, so there are no can lights. I did my best to caulk gaps and holes around wall boxes and such for the light switches and outlets. 

I still have some finishing touches (missing one door knob and some trim, and I need to build wood/drywall/green glue panel that will fit over the heat ducts and returns), but I'm mostly done. I haven't measured any sound levels to see what I've been able to accomplish. I will be doing that as soon as I'm 100% done. However, I still find it to be very good. If I'm in the basement and the furnace is running, it's not very noticable (yeah, you can hear it if you listen, but previously it was something of a roar). Also, my wife and her sister were walking and talking upstairs, and I could only hear a little of the walking. Previously, you could actually discern the words that were being said in the upstairs (well, if everything was just right, but it was pretty bad. Finally, I was playing electric guitar at a nice practice level, and my wife went upstairs and decreed that she could hear it, but that she could probably sleep through it (tentative, based on "mood of the moment". I'm sure that it will be unbearable if she wants it to be.) So there are a few subjective and quick meters that seem to indicate good results.

Before I started, I took measurements of music X at average SPL level Y (don't remember numbers, but it's written down in my "basement" file). I then went to each room and measured SPLs in those rooms. I will repeat that test in the coming weeks, and it will give a much better result to what actually happened, rather than me just saying "well, it's a lot quieter" or "you can't hear the furnace as much."

Anyway, that's where I am...


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## John Simpson (May 10, 2007)

So this *Green Glue*... it's just starting to be advertised in Australian publications. Is it really worth buying over, say, a tube of silicon? I imagine sitting a frame on a long bead of silicon would be pretty similar to what this Green Glue stuff could offer...

Or is there something about it I don't know? :dontknow:


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## bpape (Sep 14, 2006)

Separating the 2 drywall panels with any type of air gap will only cause issues. At a group of frequencies, STC will actually be worse. 

The Green Glue forms a elastic layer that also bonds the drywall together. This allows some movement of the first layer prior to the 2nd layer but also allows them to move together - though mostly out of phase with each other. There is some mass cancellation as well as some energy being converted to heat at work here. 

Also, having the first layer move independently, you gain back a little absorbtion in the mid/upper bass range which is normally lost in double drywall construction.


It's really a nice product if budget allows. Depending on frequency, you can see an increase in STC from 5-10 points. 

Bryan


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## WilliamSmith (Aug 23, 2019)

yous should choose some best acoustic material, you cant make soundproofing with ordinary ways.


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