GG then new wall or vice versa

Hello, I'm planning on soundproofing the shared wall in my room. Primarily from footstep and impact noises. I cannot hear voices through the wall, only muffled stereo when played loud and my volume is turned down. I believe most noise is coming straight through the wall and less flanking than I initially thought. Engineered floor I-Beams are not shared. The existing wall is 5/8" drywall on both sides with insulation..possibly staggered stud but unsure. Initial thoughts are to build a floating/decoupled wall (8'x12') infront of the shared wall (1/2" away from the wall) with roxul safe and sound insulation between 24" OC studs, caulked all around. My questions are: -Would I see enough performance from the wall to skip the green glue layer ? -If I was to use the green glue layer, would I put it against the shared wall or against the new drywall (infront of the roxul insulation) ? If anyone has any other suggestions I'm very open to them. Thank you and great forum you have here! Chazz

The construction you are describing will create a triple leaf. This wiill give you LESS ISOLATION at certain low frequencies. From waht you have described, it seems that music is the concern. My suggestion is to either add 2 layers of drywall directly to the current drywall, or one layer of drywall with Green Glue in between. Good luck! Andre

Thanks for the reply and info Andre. My primary concern is actually the impact noises since they are random thuds and louder than the music by far. Knowing that, would you change your suggestion to include anything else or does it still all apply just the same? Also, do you know if the improvements from green glue are much more significant as it cures from 1 day to 10 days then 30 days ? Thanks again, Chazz

reads like a spammer to me. Impact is over your head, the ceiling, so doing walls will not isolate this noise.

spammer? nope sorry...just a guy asking some questions. impact noise can come through walls from what i've read and hear at my place. I've done 1 room a week ago with some GG and am wondering how much better it's going to get before I dish out for more at 19 bucks a tube

Everything matters. And everything is what we like to have in order to get on the same page. You really haven't given any information except your opinions. What kind of apartment do you live in? What floor are you on? What kind of material is the building made of? I would take my greenglue questions to the makers website and contact them. Impact is mostly associated with footfall or "impact" type noises. Someone hitting a wall for instance. So if this is in fact the cause, then it can be from flanking at the floor level or from over head. If greenglue can or cannot help is really not the question, although you can ask it and will get several different opinions depending on ones level of experience.

More information is required to assist you. If you are hearing low frequency thumps, then the problem may be that the resonant frequency of the wall itself is being exited. Green Glue, additional layers of drywall will do little then. IF it is more midrange sound, there may holes in the wall permitting sound through. Another question is why the sound if impact is coming through the walls and not the floor. More info ton the floor construction neede also. Andre

I reopened the electrical socket in the wall to find that it must be a fire barrier in my townhouse (nobody lives above or below me) because it's cement block with some insulation and 5/8 drywall. The floor beams are engineered ibeams which seem to be cut at the walls with 2x10 blocking and mortar at the edges The problem is only low frequency thumps caused by impact, not a subwoofer/tv or stereo. Maybe they have drawers or cupboards right against the wall or something...I dunno. In this case however, would the 'bad effect' of the triple leaf wall be relevant? It seems like distancing myself from the shared wall by a layer of insulation and a floating wall may do the trick but this is why I'm here asking Thank you again, Chazz

chazz wrote:

The floor beams are engineered ibeams which seem to be cut at the walls with 2x10 blocking and mortar at the edges The problem is only low frequency thumps caused by impact, not a subwoofer/tv or stereo. Maybe they have drawers or cupboards right against the wall or something...I dunno. In this case however, would the 'bad effect' of the triple leaf wall be relevant?

The problem is that from you are describing there should not be any significant impact noise being heard. The strong suspicion is that there is some flanking going on. If that's the case, the third leaf will have little effect. If the wall's resonant frequency is being excited, then the third leaf will make things worse. Andre

The more drastic option, if you are certain that it really is coming through the wall, is to take off the drywall, on your side of the wall, use it to beef up the drywall on "their" side of the wall from the inside (between the studs), then build a new frame an inch or so away from the existing frame, and put a couple of layers of drywall on the outside of that, filling the cavity with rockwool, of course, and carefully triple-caulking all around for an air-tight seal. That would probably solve the "wall impact transmission" problem, if that's what it really is, provided that there is no flanking going on. If there IS flanking going on, then the above would not accomplish very much (except to make the TV and voices even quieter). Even then, you'd still have some flanking through the ceiling/floor/sidewalls. Not sure if it worth the effort, unless you can be 100% certain that it is ONLY impact noise coming ONLY through the wall. - Stuart -

chazz wrote:

I reopened the electrical socket in the wall to find that it must be a fire barrier in my townhouse (nobody lives above or below me) because it's cement block with some insulation and 5/8 drywall. The problem is only low frequency thumps caused by impact, not a subwoofer/tv or stereo. Maybe they have drawers or cupboards right against the wall or something...I dunno. Thank you again, Chazz

You may still have a few more areas you could check out. If you have a window in your suite and the adjoining suite also has a window that is very close in distance to it, this may be a flanking path. It could be coming from a window from a lower level as well, so that should be considered when checking. A fire break wall typically runs from top to bottom in these type of situations. But I have worked inside many an attic that had a fire break that was ruined with holes by technicians running updated services and or trying to get from one point in the attic to another side. It >could< be a possibility as it would be overhead and this could create the path...just another thought. Another thing that reveals itself is the block walls used to make these barriers are not properly pointed up, meaning there can be multiple air paths in the mortar bed that allows air/sound to leak. It would be a big task to remove the existing sheetrock to make a full discovery, but this is just information for your situation. This existing sheetrock, can you tell how it is attached to the wall? This could be the actual culprit depending on how the install was done. If you have a furred strip of wood on your side, then the other side is the same way. Basically a coupled three leaf, with the opportunity for many holes from nailing into the block. The block that you would like to think are filled with mortar, but could just as easily not be filled or only a portion of the wall cells could be filled. Then again, the way the floor joists are terminated which is most likely a framing member nailed directly to the concrete wall, the other suite side terminating in the same fashion, this could very well be the path of least resistance. Talk to your neighbor, see if they are having the same issue. Hope that helps :) Brien

XSpace gave some excellent examples of what to look for for potential flanking paths. It may seem like a daunting document but at least look at the pretty pictures in NRC IR RR 193 for an appreciation of other flanking paths. Is the impact noise from one room? If it is, has purchasing a rug for that area, if it does not have one been conisdered? This could be the cheapest way, and would not be the first time this was done. Andre

Thank you once again for all the replies. I've cut open another part of the wall in an adjacent room and have found this construction: 1/2" drywall - 1.5" pink insulation between 1.5" deep wood studs - concrete I'm sure it's the same on the neighbor's side. Seems like the mentioned 'coupled triple leaf'. I don't own the other side of the wall so buying a carpet is out. The 12 day old layer of 5/8" with green glue has cut the thumping noise by about 35% from what I can tell by ear. I would still like to improve on this.

chazz wrote:

The 12 day old layer of 5/8" with green glue has cut the thumping noise by about 35% from what I can tell by ear. I would still like to improve on this.

Great! Green Glue takes about a month to fully cure to its final consistency. Let us know how it is in a couple of weeks. Andre

Here's the update 30 days after applying the green glue: It hit it's curing time at 3 weeks, and the noise is cut down by about half, which is good, but I still have some work ahead of me to get the performance up. After even further listening, what I seem to be battling against are the slams of dresser drawers against the neighbours side of the wall. Also when their stereo is cranked, it comes through but quite muffled - almost acceptable. The next stage is to build a decoupled wall...here are my plans for the weekend, open to thoughts & critique: 1. 2x4 framing (24" o.c.) spaced 1" away from the green glue'd drywall and placed on sill foam 2. caulk around the frame 3. fill stud bays with 3" insulation 4. 5/8" drywall 5. test this out, then only if needed, another layer of GG and 5/8" drywall

Sounds like a triple leaf to me... Or maybe a quadruple leaf, if I'm understanding your previous post, where it said "1/2" drywall - 1.5" pink insulation between 1.5" deep wood studs - concrete. I'm sure it's the same on the neighbor's side." If so, and you do already have a triple leaf, then adding a fourth leaf would probably not be a good idea, unless you can spare the space for a very large air gap (many inches), and put lots of mass on that fourth leaf (several layers of drywall). Was there a reason why you didn't just take off the framing and drywall on your side, as was suggested above, and rebuild a new leaf a few inches in? That would have been the best bet, I think, from my limited understanding of the issue... Maybe André can chime in again, with his comments on that. That thin 1.5" original cavity with a thin layer of 1/2" plus your new layer of 5/8" sounds like it would be resonating at a highish frequency (small air gap, relatively low mass, poor damping), plus it is still coupled to the concrete wall. Not good at all for transmission loss in the low end. I'm not convinced that creating yet another air gap and adding yet another relatively low mass would accomplish what you want, especially seeing that you seem to think it is impact noise you are hearing. I'm guessing it would have been better to take off all the original thin coupled framing and thin drywall, like xSpace suggested, carefully seal that concrete block wall airtight, build a new frame several inches away from that concrete block wall (decoupled), then put all your mass on that (at least a couple of layers of 5/8, with GG), and fill the cavity with fiberglass or rockwool. Assuming there is no flanking going on, that should have gotten you better than what you have now, I'd say. Was there a reason why you could not do that? I'm not really sure what your options are now, but the math isn't on your side any more. You got (subjectively) a roughly 10 dB increase in isolation from increasing the mass of your third leaf by 125% and using GG. To get another 10 dB (halving the level again, subjectively), if my math is right, theoretically you'd need to do at least the same again, another 125% of the CURRENT mass, which basically means adding TWO MORE layers of 5/8 with GG. I don't think you'd want to put that much mass on simple 2x2 studs anyway, even assuming that no flanking is going on! - Stuart -

Congratulations on the Green Glue cured results. You are starting to build a triple leaf again.... There is a reason for the sticky asking so many questions, and the questions put to you in the thread. What is neede right now is more information, as already asked. Good luck! Andre