Flanking noise when treating common party wall.

Hi everyone. My topic isn't really related to building a studio, but I am almost in tears and don't know where else to turn for specialist knowledge. My ground-floor bedroom shares a common wall with my adjoining neighbours bedroom. He stays up all night as he doesn't have a job, and I am a light sleeper, so you can guess where this is going! He doesn't play loud music or anything, but just the general day-to-day activities he is doing is keeping me awake ( normal TV volume, opening wardrobe doors, light switches being flicked etc). I cannot expect him to change his nocturnal behaviour, as technically he isn't doing anything wrong, so I have spent a few weeks reading up on this forum in the hopes I can do something about this problem from MY side of the party-wall. Here goes : I understand the way to maximum sound-isolation is a room-within-a-room approach, but don't think I can really consider this. Partly because my room is tiny and already has very low ceilings, but also because a completely air-tight room wouldn't be very practical for sleeping in. I was considering getting a single stud-wall built a few inches away from the shared party-wall, insulating the 4" space with Loft-insulation to deaden the cavity, and then seal with perimeter with acoustic caulk. This would treat the party-wall (where I guess most of the noise is coming from), but I would still suffer from flanking noise transmitted across the ceiling and sidewalls, which are obviously coupled to the party-wall. What I want to know is, would this go some way to reducing the amount of noise I could hear from next-door or would the effects of a single stud-wall be negligible due to flanking on the sidewalls/ceiling? I could happily live with a 70% reduction in noise if a single-stud wall would help, but if it would make no difference due to flanking, I might as well not bother. I'm also not sure that an air-tight room-within-a-room would be such a good idea for sleeping in. So I don't really know what else I could do? Details: Concrete floor both sides of party wall. Shared brick wall without a cavity. Rendered with plaster both sides. Room size 4m x 4m x 2.2m high. Level of incoming noise is normal TV volume, wardrobe doors, things being moved about etc. My budget is about £500 GBP. I would be so grateful for any advice or suggestions you could give me. I hope you will still help me even though this is not exactly a studio build. Sorry for imposing on a studio building forum, but I guess a general builder wouldn't have this kind of specialist knowledge. Regards Sarah

Hi Sarah, and welcome! It sounds like you are pretty desperate! I hope someone here can help you out, and I suspect that your problem might be treatable at reasonable cost. First, a question. You say that the floor is concrete, the wall is a single layer brick wall, but you didn't mention the ceiling, and that might be a part of your problem. A single layer brick wall should be doing better than what you described (unless there are holes in it, or maybe deep cracks, or it is just badly built), and likewise for a concrete floor, so I'm wondering if maybe the ceiling might be a part of the problem. What is that made of? And also, what is above it, and what is between your ceiling space and his? It occurs to me that perhaps there is a shared open space above the ceiling, and that is where your issue is. Do you have any way of checking that? Can you get access to the space above the ceiling, to see for yourself, physically, if there might be a common airspace up there? Finally, how about windows? Do both apartments happen to have windows that are close to each other, or maybe face the same exterior solid surface? I'm wondering if maybe there is a shared airspace outside, with your window and his window, both looking into it. Even worse would be if there was a solid wall in that space, outside both windows, that might be reflecting sound. Ditto for doors in a shared passage. Perhaps you could sketch out the details of the two rooms (size, orientation, windows, doors, etc) so we can get an idea of the layout, and try to figure out where the real problem(s) might be. One final question: What is under the floor? You said that it is a shared concrete slab, but is it sitting directly on the ground, or is there something underneath it, like a crawl space for example? And how thick is it? - Stuart -

I am also a light sleeper. There may be some construction you can do to reduce noise, but nothing is cheaper or more effective than earplugs. They work for me. Best luck.

A while back, I helped paint a layer of Gyprock, that was put up against a brick wall, that was shared by a neighbour. To this day, I can still hear what appears to be someone using a choppingboard in a kitchen. What a design failure! Later on, I always wondered, what if the gyprock was attached to the brick wall with green glue? Could that solve minor flanking problems...

Hi Stuart, thanks so much for expressing an interest. The Ceiling is 2.2m high and is a single layer of plasterboard attached to joists that run towards the shared party-wall. When I looked in to the loft, it looks like the ends of the ceiling joists are built sitting into the actual brickwork in the party-wall rather than sitting in metal hangers (I think that’s what they are called). I can't see if the neighbours joists are touching against mine and that is coupling them together? This is possible though, as I can sometimes here my neighbour when I am in my hallway, which shares the same common joists as my bedroom. I'm guessing that this means I will most definitely be getting flanking noise from the ceiling as well as the side walls ? It doesn't sound like noise is coming from the ceiling when I am lying in bed though. Could it be that the wall offers less isolation so I notice this more than the ceiling, but they are both contributing factors? The brick party-wall continues right up to the roof tiles, so its not a shared space. I did notice that the bare brickwork up there is really poor as the builders haven't bothered to fill up all the gaps between the bricks with mortar. I cannot stress how large the gaps in the mortar are. I'm guessing that this poor workmanship continues downwards into the actual rooms and might explain why the brick wall isn't giving as much isolation as you'd expect ? I know the floor is concrete, but not sure if its one big slab and they have built the party-wall on top of it, or whether they built the party wall up from the foundations, and then poured a floor either side? There isn't a cavity underneath though. We both have windows in the same wall, they face onto a road and not onto any reflecting surfaces opposite. I have drawn a plan in Paint, hopefully this might give you a better idea? Thanks so much for everyones interest. Sarah .

Hi Sarah.

It doesn't sound like noise is coming from the ceiling when I am lying in bed though. Could it be that the wall offers less isolation so I notice this more than the ceiling, but they are both contributing factors?

Very likely! Plus, sound is elusive: It can seem to come from places where it actually isn't, and not seem to come form the places where it is. Have you ever taken your car to the mechanic, swearing that there is a strange noise in the engine, and two days later the mechanic calls to tell you he fixed the problem by replacing the damaged bearing in your rear wheel? It may sound like the wall is the issue, but the problem might actually be coming from elsewhere in your room. For example, it might be the coming from the ceiling and bouncing off that wall, at just the right angle that, wen you are lying in bed, it seems to come from the wall. Of course, it might actually be coming from the wall! Now, please don't take my comments here as being those of an expert: I'm not an acoustic expert. My comments and suggestions are only based on what I've learned over the last few months and years. I'm hoping that some of the real experts here can chip in and comment on my comments, just to make sure I'm not leading you astray! At first glance, I would guess that the common wall is one problem, the ceiling is another problem, and the "window" and "door" walls are additional problems, most likely in that order of importance. So, if I were in your situation, I think what I'd do is first rip the ceiling off, install resilient channel (RC) across your joists (or alternatively iso-clips and hat channel, but NOT hat channel by itself), stuff several inches of rock wool or fiberglass insulation up there in the space above, then hang a couple of layers of 5/8 sheetrock from the RC, taking care not shirt-circuit the RC with your screws. If you had a few more dollars in your budget, you could perhaps consider using Green Glue between those layers of sheeetrock, but I don't think it is necessary in your case, since it doesn't sound like low frequencies is the issue (except maybe for the impact noises? light switches, closet doors...). With this new ceiling I'd be very careful to make sure that the sheetrock does NOT touch the shared wall! It came close, but make certain there is a small gap there, and fill it with acoustic sealant. You want as little chance as possible for flanking from that wall. Ditto around the edges, where the new ceiling meets the existing walls. Stagger the joints on the two layers of sheetrock so that they do not line up, use backer rod in the gaps between the sheets, caulk, tape, mud, sand, seal, paint, etc. do NOT install light fixtures that require you to drill large holes in the ceiling, and only attach lights where there is RC above to screw into, taking care to avoid short-circuiting the RC with screws. In fact, if you can then don't mount lights on your ceiling at all! Use wall indirect lighting that bounces of the ceiling, maybe from wall lights, pedestal lamps, etc. OK, this isn't a huge deal, and you can screw something up there if you want, as long as it only goes into the RC but anything you can do to minimize perforating your ceiling will be good. Next, seal that common wall! It sounds like it might not be very well built. Strip the existing paint off it, down to bare cement/brick/whatever is under the paint. If your budget can handle it, you might want to consider adding a thick layer of "interior plaster". I'm not sure what you call it in your part of the world, but where I live it comes in heavy one-gallon and five-gallon buckets, and it is like a very thick acrylic-based paste, that you layer on smoothly with a trowel, then sand flat when it is dry. You have to work carefully to keep it flat and smooth while you put it on, since it is a real bitch to sand properly, and the dust is a nightmare. Anyway, when you have that done, seal it with a couple of layers of sealer (undercoat). Make sure that you seal it well, right out to all the edges. In fact, thinking about it, I might have the construction sequence wrong here: you probably want to do this wall plastering/sealing while your ceiling is still ripped off, so that you can get up as high as possible above the new ceiling line, to improve your seal. I hope that makes sense! If you are going to do the side walls too (see below) then do this wall with those side walls open too, so you can get right up to the edges. Now, build your new stud wall a couple of inches in from the common wall, make sure the stud frame does NOT touch the common wall at any point, not even from a stray nail. Fill the gap with rock wool, and put up a couple of layers of 5/8 sheetrock on the studs. Stagger the joints, use backer rod in the joints between the sheetrock, and seal all those gaps, as well as the gaps around the around the edges, with acoustic sealant. Tape, mud, seal, paint and decorate to taste! I expect that should take care of a large part of the noise. hopefully, that's all you'll need to do. There might still be some flanking through the "window" wall and the "door" wall, but I'm hoping that it won't be a major issue. If it is, then the cure for that is a little more complex: Take off the sheetrock from the inside of those walls, carefully, cut it to size to fit between the studs, and put it back inside the wall, between the studs, up against the sheetrock on the other side. Hold it in place with cleats, and seal around the edges with caulk. Put RC (or iso-clips plus hat channel) on the studs, fill the air space with rock wool or fiberglass, and hang a couple of layers of 5/8 sheetrock. Backer rod, caulk, tape, mud, seal, paint, etc. And if you STILL have issues, the next step would be windows and doors. Hopefully it won't come to that, as good windows and doors are costly. Personally, I suspect that just doing the ceiling and common wall will be enough to get the sound down to acceptable levels, since it isn't all that loud: just annoying. One word of caution: you need to work carefully, and make certain that things are sealed up as tight as you can make them. You do not want gaps anywhere, since sound easily leaks through even the tiniest gap, as you have already discovered! So buy good acoustic caulk for sealing up the wall/ceiling and wall/wall gaps, and use it liberally, as directed on the tube. Ditto with the caulk: apply it liberally, don't skimp. Make sure you get it in every little nook and cranny, and is smooth and well stuck. Etc. OK, that's what I would do. I'm hoping that the acoustic and construction experts can now add their own comments, and either confirm what I suggested, or flame me to a smoking crisp and tell you what you REALLY need to do! One final suggestion that might help, and will be much cheaper than all of the above: Have you tried masking the noise? You can buy various gadgets these days that generate all sorts of white noise and variations on that theme, such as the sound of the ocean, waterfalls, rain forests, etc. Maybe just putting one of those on your bedside table will do the trick. White noise is soothing, and induces drowsiness. It can also mask underlying noises, such as loud TV and light switches from the next room! It only needs to be about 3 dB louder than the background noise in order to mask it completely, and even much lower levels can work wonders. Some people hate those gadgets, some love them. It might be worth a try. - Stuart -

PS. I just noticed that your diagram has the "door" wall labeled as being "block", so skip the part where I suggested it was a stud wall: If you have to solve that "door" wall problem, then you'll need a stud wall there too. You can't just put RC directly on the block: it won't work, and might even make things worse. There has to be a decent air gap of several inches in order for RC to work. Hopefully, you wont need to do that wall at all, but if you do, then ignore the comments in my previous post about treating it as a stud wall. - Stuart -

Sarah, The brick wall itself - as a single leaf - is a lousy isolator. The concrete floor will do you pretty well for the types of sounds you're complaining of - I would not suspect it to be the cause. I wouldn't bother with an entire wall in this case - but would opt for installing RSIC clips and metal hat channel directly to the face of the existing wall - and then installing a couple layers of drywall over that. Making sure to caulk the edges of the wall to ceiling (to floor - to walls) to make certain no air passages exist. Sound travels easily where air can go. Now - as far as the ceiling goes - yes that could well be a coupling point - the suggestion to remove the existing drywall and add resilient channel is a good one - although you could probably acheive your goal with just an additional layer of drywall and green glue. The reason why I do not sugest getting carried away with the ceiling as compared to my recommendation for the wal, is because it is already a 2 leaf system - with the joint at the wall (meeting the ceiling) being it's weak point. I have no doubt that this would handle the sound at the levels you are speaking of. Rod

Lucky girl, Sarah! Rod took an interest in your problem. Listen to him. He wrote the book on this kind of construction. Literally. Rod's book is our Bible here! Rod, I'm curious about your suggestion of putting RC directly on the brick wall. Andre posted a link to NRCC-44692 a few days ago (full title: "A Simple model of the sound insulation of gypsum board on resilient supports"), and I've been reading through that. In there they say that in order for RC to be fully effective, it needs to have a good air gap behind it. They tested 8 cases of RC attached over a hard surface, with gaps ranging from 13 mm to 286 mm. They suggest that 75 mm seems to be the point where you start getting maximum effectiveness. At 13 mm, all you are really getting is decoupling, while at 75 mm you are also getting the benefit of the air gap, according to that paper. (Beyond 160 mm, there isn't much additional benefit at all. Diminishing returns.) In this particular case (Sarah's wall), I assume that it's OK to put RC directly on the wall since Sarah doesn't need all that much isolation (as compared to a studio), and simply making her wall 2-leaf with RC for decoupling is going to do the trick? Is that it, or is there another reason behind your suggestion? - Stuart -

Rod, Ms. Sarah also mentioned "I cannot stress how large the gaps in the mortar are. I'm guessing that this poor workmanship continues..." wouldn't this be a good time to point these areas up, before the risc clips/hat channel and additional mass was added?

Stuart, most importantly - I did not recommend that she use RC on the wall - but rather RSIC 1 with metal hat channel. Although not 75 mm - that installation is 41.275 mm from the face of wall to inside face of new drywall - and thus even if it is not at the maximum benefit - it is a long ways beyond the 13 mm of a standard resilient channel. I would expect to see anywhere from a 12 to 15 STC increase in a single whythe brick wall using the RSIC-1 clips. That number (however) would not account for flanking issues - which is why I also recommend some additional work on the ceiling. Sincerely, Rod

Thanks Rod! That makes sense. My bad, for not reading what you actually said, and just thinking I had... Sigh! One day I'll learn to pay attention better. Figure 10 in that paper confirms your numbers: 41mm cavity depth is easily in the range 10db to 15db increased transmission loss. Your insight is always appreciated. Would there be a worthwhile benefit for Sarah to use Green Glue between the layers of sheetrock on that wall, or would the cost not be worth the benefit? - Stuart -

Thanks so much to Rod and Stuart for their fantastic responses. I've just been reading through many previous posts to learn more about installing RSIC and Hat Channel and am very excited about this!!! Following on from your recommendations, I shall make arrangements to have the existing plasterboard removed from the ceiling and then have RSIC/channel installed on the joists and party-wall, and then hang 2 layers of Plasterboard+Green Glue in between. Green Glue sure is expensive - there seems to be only one suppler in the UK : http://www.stoneaudio.co.uk/ - £166 for 12 tubes!! Are there any similar products to RSIC that are made in the UK and known by a different name? I see that RSIC are made by the following company but they have no distributors outside the US /Canada that I can find ? Any UK recommendations ? http://www.pac-intl.com/rsic.htm Thanks once again to Rod and Stuarts taking time to provide expert advice! Thanks kindly guys! Oh - just edited this post to say that I just found this product available in the UK, but it only creates a space of 35mm from existing wall to the new plasterboard (drywall). Not sure how good it is, or it it will be as suitable as RSIC clips, but I might not have any choice unless someone knows where I can get a good alternative to RSIC+Hat channel in the uk. http://www.cmsacoustics.co.uk/c-acoustics/isomax.htm

Sarah, you'll be fine with the iso-max clip..... I do not think you really need green glue in this case - 2 layers of 16mm drywall over the hat sections should be enough to get the job done. Rod

Oh - just edited this post to say that I just found this product available in the UK, but it only creates a space of 35mm from existing wall to the new plasterboard (drywall). Not sure how good it is, or it it will be as suitable as RSIC clips, but I might not have any choice unless someone knows where I can get a good alternative to RSIC+Hat channel in the uk.

I'm not 100% certain here, and I'm sure Rod can tell you for sure if you need it, but if you are concerned about the depth then maybe the easiest thing is to just put some 1x2 or 2x2 lath strips on the wall first, then attach the RSIC clips to that. It would give you plenty of extra depth, and would not cost much. More space for rockwool, too. - Stuart -

Sarah fyi - You can also try RPG Europe ( http://www.rpg-europe.co.uk/ ) as a supplier of Green Glue, if you need it. The quote i got (October 2007!) was £9 per tube. rgds

Hi all. Got almost everything I need to start the actual works but just have a questions about the Plasterboard/Gyproc. I intend to use two layers of 12.5mm Plasterboard (+greenglue in-between) for the wall, but should I use two layers of 9.5mm or 12.5mm plasterboard for my ceiling application? More mass seems to be a key factor in reduction, but I am worried about the whether the Isomax clips will be okay to hold the weight 2 layers of plasterboard. Each clip is rated at 22.5kg, and I will be using approx 30 clips on the ceiling joists. Also, should I be using self-tapping screws when fixing the boards to the channel, or will normal plasterboard screws (for wood frames) be okay ? Thanks very much, Sarah.

Sarah E wrote:

I intend to use two layers of 12.5mm Plasterboard (+greenglue in-between) for the wall, but should I use two layers of 9.5mm or 12.5mm plasterboard for my ceiling application?

Sarah, your best bet would be 2 layers of 16mm (in both locations)- under no condition would I use less than he 12.5 mm if I were you.

More mass seems to be a key factor in reduction, but I am worried about the whether the Isomax clips will be okay to hold the weight 2 layers of plasterboard. Each clip is rated at 22.5kg, and I will be using approx 30 clips on the ceiling joists.

Isomax CLips will handle that load and more without any issue.

Also, should I be using self-tapping screws when fixing the boards to the channel, or will normal plasterboard screws (for wood frames) be okay ?

You need to use a self tapping, bugle head drywall screw for metal frame applications. Rod

Thanks Rod, and everyone, for you kind replies. Hi Rod, I have no experience in construction, and I am naturally concerned about the weight of 2 layers of 12.5mm plasterboard, plus a coating of finishing plaster, hanging above my bed. Can you, or anyone, put my worries to rest and help me with these questions ? 1. I shall screw the Isomax clips into the Ceiling joists using two wood screws per clip. The joists are 100mm deep, so if the screw goes into the wood approx 50mm, will that be enough? 2. The first layer of 12.5mm plasterboard is screwed into the Hat-Channel using 38mm screws. The second layer of 12.5mm is ALSO screwed into the Hat-Channel, but using longer screws (65mm) that go straight through the first layer of plasterboard. Am I using the right length of screws or are they too long really (38mm + 65mm)? 3. Rod said to use self-tapping. Is this the same as Self-Drilling that I have found below? There seems to be a choice of Fine or Course screws too. I don’t know which ones to use? I read somewhere that the self-drilling ones can tear up the channel and that Fine screws were the ones to use on Hat-Channel or have I miss-understood? http://www.screwfix.com/prods/27940/Scr ... ck-of-1000 http://www.screwfix.com/cats/A331389/Sc ... all-Screws 4. Will the Clips and Channel definitely hold two layers of 12.5mm Plasterboard and a 3mm coating of finishing plaster ? I respect Rod as he is an expert but I cant help but worry - :) Thanks so much for your kind words of help! Sarah

Hi Sarah, If Rod says it will work, then it will work. Just one note of caution: Be very careful with your plasterboard screws to make sure that none of them go into the joists! That would "short circuit" the clips entirely, making all your hard work for nothing. You need to make absolutely certain that your screws go ONLY into hat channel, and don't come near the joists. Since you wont be able to see where the joists are accurately once you have the plasterboard in place, and especially for the second layer when you can't see them at all, you need to mark the positions of the joists and the hat channel on your WALLS, right below the ceiling. You can even snap chalk lines across the plasterboard if you need to, to make it easier to know exactly where the joists and hat channel are. Ditto for your wall. - Stuart -

Sarah E wrote:

1. I shall screw the Isomax clips into the Ceiling joists using two wood screws per clip. The joists are 100mm deep, so if the screw goes into the wood approx 50mm, will that be enough?

Isomax requires #8 x 2.5" coarse screw. That would be a 65mm screw.

2. The first layer of 12.5mm plasterboard is screwed into the Hat-Channel using 38mm screws. The second layer of 12.5mm is ALSO screwed into the Hat-Channel, but using longer screws (65mm) that go straight through the first layer of plasterboard. Am I using the right length of screws or are they too long really (38mm + 65mm)?

USG requires at least 5/8" of penetration (16mm) so for 5/8" drywall (instead of your 1/2") it woud be 32mm and then an additional 14 mm for the 2nd course or a total of 48 mm....... your 2nd layer screw is WAY too long....

3. Rod said to use self-tapping. Is this the same as Self-Drilling that I have found below? There seems to be a choice of Fine or Course screws too. I don’t know which ones to use? I read somewhere that the self-drilling ones can tear up the channel and that Fine screws were the ones to use on Hat-Channel or have I miss-understood? http://www.screwfix.com/prods/27940/Scr ... ck-of-1000 http://www.screwfix.com/cats/A331389/Sc ... all-Screws

There is a difference between drywall screws for wood and drywall screws for metal. In the States a drywall screw for metal would be a Buglehead type S - for wood it is a type W - so you want an S type screw - and that will have a fine thread - you never use a coarse thread on a steel stud.

4. Will the Clips and Channel definitely hold two layers of 12.5mm Plasterboard and a 3mm coating of finishing plaster ?

2 layers of 16 mm drywall (which i really what you should use) weight roughly 10 pounds per square foot - and 3mm of finishing plaster weights .21 pounds....... that's a total of 10.21 pounds per square foot. According to Isomax:

Load Specification for IsoMax Clips The IsoMax clip is designed to carry a drywall furring channel (hat track) with one or more layers of gypsum wallboard attached. THE LOAD CAPACITY OF THE CLIP DEPENDS ON THE GAGE OF FURRING CHANNEL USED. Lighter, 25 ga, furring channel carries less load than 22 ga channel. The maximum design load capacity for the IsoMax clip in shear (wall application) or in tension (ceiling application) is as follows. Design load calculations are based on tested loading to failure where the furring channel deforms and pulls out. Design Load Maximum for Wall or Ceiling Application ................................................................ 2:1 safety factor....... 2.5:1 safety factor* IsoMax clip with 25 ga steel furring channel.............. 45 lbs......................... 36 lbs. IsoMax clip with 22 ga steel furring channel.............. 60 lbs......................... 48 lbs. Note: 5/8" thick gypsum wallboard weighs 2.3 lbs/sq ft. 1/2" thick gypsum wallboard weighs 1.85 lbs/sq ft. * Suggested safety factor of 2.5:1 for more critical life safety applications; i.e., hospitals

Thus the manufacturer rates these for a 90 pound per square foot load with 25 ga hat section) - and our total load of 10.21 is working with a safety factor of 8.9:1............ (they consider 2.5:1 to be adaquate for hospitals........ we beat that by more than 3 times the safety factor.

I respect Rod as he is an expert but I cant help but worry - :)

Understandable to be cautious. I hope this helped. Rod

Soundman2020 wrote:

Just one note of caution: Be very careful with your plasterboard screws to make sure that none of them go into the joists! That would "short circuit" the clips entirely, making all your hard work for nothing. You need to make absolutely certain that your screws go ONLY into hat channel, and don't come near the joists. Since you wont be able to see where the joists are accurately once you have the plasterboard in place, and especially for the second layer when you can't see them at all, you need to mark the positions of the joists and the hat channel on your WALLS, right below the ceiling. You can even snap chalk lines across the plasterboard if you need to, to make it easier to know exactly where the joists and hat channel are.

Stuart, Actually - although this is true with both RC-1 and RC-2 - it is impossible to hit a stud using the RSIC clips and the right length screws First off - the clip itself protects the stud....... Next - it is 1 1/8" from the face of stud to the back of drywall - and you only need 5/8" penetration of the metal for the screw. This is a foolproof system. Rod

Thanks Rod! You live and you learn! And once again I'm confusing RC with RSIC clips! Sigh! :oops: - Stuart -

Hi everyone, So, the original plasterboard was removed from the existing ceiling to expose the joists, and then the Isomax clips were screwed to these joists and horizontally across the party wall. You cant get 5/8 plasterboard from the local builders yards in UK ( or so it seemed to me) so I settled for two layers of 12.5mm thickness ( sorry Rod :( ) The first later was screwed in, at 150mm intervals. Once both the new wall and ceiling were up, the gaps between the edges of the boards were filled with a plasterboard filler (mud??) and then sanded smooth so there were no protruding bits. A second layer was then installed over the first, with a tube of GG being used on each 8x4 sheet. The joins in the first layer did not co-incide with any joins in the second layer. Great care was taken that the screws used on the second layer did not hit any used in the first layer. Also, as per Rods recommendations for screw length, the screws could not have short circuited against the original wall. 1) The existing walls were not totally square and the plaster on the walls was quite bumpy, so the gap left between the new plasterboard and the original walls/floor etc varies from 3mm-14mm, I hope this is okay ? 2) The gaps now need to be filled with Acoustic Caulk. I cant seem to find Backer-rod ( Caulk-saver) so am I okay just to squirt loads of Caulk into the gap until it fills up ? 3) I hope I have done everything correctly. Can anyone see if I have made any mistakes in my description above? The noise from neighbour is no different, but I'm guessing that's because I have not caulked the edges yet and so the new wall is not air-tight? Thanks, Sarah.

Sarah, you said new walls - so you did those before putting up the ceiling? You really need backer rod otherwise the odds are greatly against you when it comes to the caulk failing. I find it hard to believe that no one carries it. have you already caulked the perimiter of the walls as well? In a room - all 12 edges need to be caulked / sealed in order for the room to seal. Rod