Best way to use Green Glue in my situation? - AVS Forum
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post #1 of 14 Old 05-08-2013, 11:45 AM - Thread Starter
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Hi All,

This is my first post, hopefully I'm putting it in the right place.

I've long been looking at Green Glue, have read all the data and I'm pretty much convinced it's the product I want to use. My question comes down to what your opinions would be on the best way to use it.

I own an end unit of a townhouse and I want to soundproof the shared party wall with my 1 neighbour. Just to be clear, they are not "overly" noisy, but I do hear voices at times, yelling at the TV during hockey games, and occasionally hear their TV, etc. It's not like I'm trying to soundproof their bass guitars or anything like that. It is, however, to the point where I do notice it, and I'd rather not. The party wall is double wall, regular fibreglass insulation in between, 1 layer of 1/2" dryall on each side of the wall (not much!). It's minimum code construction.

I have roughly 3 inches to work with on this shared wall (any further outwards than that and I would be on the staircase). What would everyone consider to be the best application...

1) Removing the existing 1/2" layer of drywall, adding wood strips around the top, side and bottom studs, and basically converting this wall to a staggered stud wall. Then adding two layers of 5/8" drywall with Green Glue in between.

2) Simply adding a layer of 5/8" drywall onto the existing layer of 1/2" drywall with Green Glue in between.

3) Adding a layer of 5/8" drywall over the existing 1/2" drywall, then ANOTHER layer of 5/8" drywall with Green Glue over that layer (3 total layers of drywall, 2 layers of Green Glue).

I'm leaning towards option 1, based on my research it seems like the best solution given my constraints. I just want to make sure I'm not missing anything. Option 3 also seems like it would work, but perhaps more costly.

I also realise that Green Glue isn't a miracle cure, I just want to make the most improvement possible for the least amount of money.

Thanks in advance for any advice!
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post #2 of 14 Old 05-08-2013, 02:37 PM
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Hey Maple22, welcome to the Forum.

Usually to do a staggered stud wall you would start with a 2x6 top and bottom plate. But let's assume that you furred out the top and bottom plates one inch with fire caulking on all seams to preserve the fire rating and inserted new 2x4s at the midpoints of each studbay in the existing wall, that would work to create the separation, but is one heck of a lot of effort.

You could also entertain the thought of ripping out the existing drywall and using RSIC-01 clips with 25 gauge hat channel and then two layers of 5/8" with Green Glue in-between as the ultimate solution soundproofing solution (including putty pads around receptacles and acoustic sealant along all edges and gaps. The linked document shows 1 5/8" as the total height of both the clip and the hat track. Adding two layers of 5/8" drywall with Green Glue in between the layers will give you exactly 1/8" to spare out of your 3" of working room before interfering with the steps. WITH THIS METHOD YOU WILL NEED TO RECREATE THE FIREBLOCK WITH 5/8" TYPE-X DRYWALL OR FIRE RATED EXPANDING FOAM SEALANT FOR THE GAP CREATED BY THE RSIC-1 CLIP AND CHANNEL.

But out of your 3 choices above, I would say option 3 is the easiest to accomplish. The only tweaks I would add are Green Glue between each successive layer, not just the last layer and acoustic sealant around the perimeter since you would be leaving an 1/8" gap between the edge of the new layers of drywall and the existing drywall. Soundproofing company has a document HERE and sells the sealant HERE.

Good luck!
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post #3 of 14 Old 05-08-2013, 02:39 PM
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You have good options for that single wall, but sound follows more than one path. It will help, yes, but do realize that sound is also coming "into" your space through the ceiling and through the floor. Look up Ted White (the Green Glue man himself) here on the forum and speak with him directly.
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post #4 of 14 Old 05-08-2013, 03:06 PM - Thread Starter
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Thanks TMcG and warren. I do realize that the sound is following more than one path into my space, but after careful listening is does seem like the bulk of it is coming through the drywall itself.

The furring strips would be more work, maybe even more work than is necessary for what I'm trying to accomplish. I just figured it's probably the most complete way to go given what I have to work with.

Would 2 additional layers of 5/8" drywall with successive layers of green glue give similar results to furring and decoupling the wall in option 1? Or is decoupling first far superior?
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post #5 of 14 Old 05-08-2013, 03:32 PM
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Soundproofing has four major components: Mass, damping, decoupling and absorption. The more ways you use to address the issue, the better. And of course there is good-better-best within each technique, generally speaking.

I think only a lab could answer your question specifically about the exact differences, but the decoupling solution using the clips and channel is better than a staggered stud wall. The best decoupling option is a completely separate wall, of course.

Adding layers with Green Glue will get you mass and damping, but not decoupling or absorption. Using staggered studs will obviously get you some decoupling but not as good as the engineered solution. Realistically, you won't get absorption unless you put acoustic panels on the surface of the new wall, but even then it will only have a real effect on frequencies down to the midrange area and do nothing for bass waves and lower midrange.
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post #6 of 14 Old 05-09-2013, 06:15 AM - Thread Starter
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I came across this thread last night. Makes me nervous about NOT furring, as if I don't remove the original drywall, I could be throwing money into the project without knowing what's really behind that original drywall. That poster was trying to accomplish exactly what I'm trying to accomplish.

http://www.avsforum.com/t/1123532/green-glue-question
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post #7 of 14 Old 05-09-2013, 06:52 AM
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With the clips you wouldn't be furring, only adding them directly to the original studding while affording you the opportunity to see what is behind the wall. But since the clips hold the drywall away from the studding and this is a fire wall we are talking about, you will have to do fireblocking.

I wouldn't worry about what is behind the original wall, especially since you did a bit of exploratory work and found out that it is insulated. Your home was fully inspected and passed inspection before the walls were closed, so no sense in fretting. The question then becomes if you simply slap up two layers of 5/8" with Green Glue or go full-bore with gutting the wall, clips, channel and two layers with Green Glue or even just three layers of 5/8" with Green Glue in between the layers. The choice and budget really yours.
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post #8 of 14 Old 05-09-2013, 08:50 AM - Thread Starter
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Thanks TMcG, you're a big help smile.gif

I just checked with my local building and planning city official, who gave me a little info on the type of wall which I'm dealing with. From my neighbour's place to mine, it would go something like this...

1/2" fire rated drywall > studs > more fire rated drywall > studs > 1/2" fire rated drywall on my side

Would this mean that the wall is already somewhat decoupled and that I may be perfectly fine with just adding more layers of drywall with green glue? If I recall correctly, I believe Ted White posted somewhere that this type of construction already represented a decoupled wall (but I could be wrong).
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post #9 of 14 Old 05-09-2013, 10:03 AM
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Yes, that's the code in many areas only he/you left out the part about a 1" minimum air gap. If you are saying there is not an air gap, then I would be surprised. Here is an illustration:
Extracted on 21/09/2001

By removing the existing drywall and installing clips and channel to further decouple (beyond the existing air gap), you are inviting yourself into a lot more work to preserve the firestop using furrings, foam and drywall to bridge the new gap.

Reviewing my posts I didn't really give you my opinion of what I think you should do, only present options and the challenges with each. If I were you, I wouldn't touch the existing wall and simply add two layers of 5/8" on top of the existing (make sure you are hitting the studs on both layers!!) with Green Glue between both layers and acoustic sealant at the edges and call it a day. You will likely get no large further benefit from additional decoupling. Adding mass and damping is the simplest and the best way to go. Just my 2 cents.
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post #10 of 14 Old 05-09-2013, 10:16 AM - Thread Starter
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The illustration helps, and after learning this I completely agree with your advice. I think any further decoupling is overkill for what it's worth, and I think I'm just going to add the extra layers on top with successive layers of GG.

I hope to get started on it this weekend, thank you for your help and advice!

On a side note, I'm a little surprised that I can hear what I hear given this type of construction, but I'm also more hopeful that the adding of layers with GG should really help with airborne transmission.
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post #11 of 14 Old 05-24-2013, 12:01 PM
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The reason for the current sound transmission is partly due to the triple leaf there and the now-higher resonance frequency of the system. Smaller air cavities have higher frequency resonance points, well into the vocal range. So while decoupled, you have 3 smaller air cavities hurting you at higher frequencies. The overall system lacks mass, and lastly, the undamped drywall has a coincidence point at 3100 Hz, again not helping the cause.

Given the flanking that exists, it would likely be a waste to dismantle and install clips. While that’s the best solution given your space, the flanking will likely ensure you never see the full potential of such a wall.

So given the diminishing performance returns, the added cost, as well as the fire-rating issues TMcG mentioned, I would suggest 1-2 sheets of drywall and damping compound.

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post #12 of 14 Old 05-24-2013, 04:52 PM - Thread Starter
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Slight modification to the way I described the wall, and slightly different from the diagram above.

There is no drywall in the middle of the two walls, so it looks like this...

5/8 Drywall > 2x4 stud > 1" air gap > 2x4 stud > 5/8 Drywall (studs are staggered on the two walls)

So in this wall there should not be a triple leaf correct? Not that it changes my decision, I'm still adding extra drywall and green glue, more of just a curiosity thing.

Thanks for the help guys, I hope to be starting this within the next week or so.

Oh, and sealing around electrical boxes.... is using green glue sealant on the gap between the drywall and the rim of the box sufficient, or is wrapping the box in a putty pad far superior from a soundproofing perspective?
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post #13 of 14 Old 05-24-2013, 07:21 PM
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The putty pads are far superior from a soundproofing perspective. However, to properly retrofit you will have to open up a drywall "window" around the box, install the putty pad around the electrical box and then patch the drywall hole. If you are careful you can re-use the same piece for the patch. The good news is that your patch job wouldn't even have to look perfect. Only one or two coats with some mesh tape and that's it since you will be covering it over with fresh drywall anyhow. I would still use a sealant around the box edges.

To avoid using box extenders, if you are opening up the wall I would probably just replace the outlet box completely with an adjustable one like this http://www.homedepot.com/p/Carlon-1-Gang-21-cu-in-Adjustable-Electrical-Box-B121ADJ/202077339#.UaAeT8u9KK0 for two reasons: 1. You can encapsulate all sides of the box with the putty pad, including the side against the stud and 2. The box will adjust outwards until it is flush with the additional layers of 5/8" drywall.

Either way you go, good luck with your project!
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post #14 of 14 Old 05-25-2013, 11:11 AM
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Option 2 is certainly easiest and cheapest I'd think.

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