Terrace basement: drywall riddle...

well I'm exhausted, but getting there! I've been putting up resilient channel, but have a query. The advice I read online was to use 400mm centers between the bars, which is great if you're using 1200x2400 but I'm using 900x1800, so if I do 400mm centers, my boards won't join over a bar. If I reduce the centers to 300mm, I will still have 4 bars per board (when using lengthways) as per the 400mm centers on 1200x1800 - but will this mean the boards are getting too much support from the bars ie the resilience will be less and this will negatively affect my soundproofing? Would I be better to go with 450mm centers ie just have 3 bars per width of a board? Then I worry about not having enough support for my 2 layers of drywall though... Thanks for your knowledge! PS someone might be giving me an old BBC studio door : ) PPS any tips on levelling an uneven concrete floor?

bump :D any resilient experts out there?

The verdict from the manufacturers tech helpline is don't go over 400mm centers, but less is fine, it won't affect the acoustic properties. So I'll be going for 300mm centers, which will mean 4 bars per 900mm board, and they'll join on a bar.

another res bar question: should they overlap (by how much) where they join, or just buff up to each other? The supplier is open again tomorrow so I can call tomorrow, but any responses today would be great!

for reference: the resilient bar should buff up to the next one, but not overlap

I'm building a stud wall up against a sloping wall. Vertical 4x2s will attach to horizontal 4x2 on the floor and a ceiling joist above. When vertical 4x2s are exactly vertical, the air space at the bottom of the wall will be 4", but at the top it will be 8". If this gives an average air space of 6" will the wall's soundproofing effect be equivalent to that of a wall which has a constant 6" air space? If I use the vertical 4x2s on their sides ie 4" side against the wall (not touching) there will be a 2" air space at the bottom of the wall and a 6" air space at the top of the wall. If this gives an average air space of 4", will the wall's soundproofing effect be equivalent to that of a wall which has a constant 4" air space? The reason for asking is that my doors are in the corners of the room so the deeper the stud wall, the narrower my doorway gets (and it's getting pretty narrow already!) Thanks as always for the advice. And as always I'm posting at the last minute with a drywaller coming tomorrow to help me out : )))) cheers

anyone : ))))

4" looks more than enough to me. Ofcourse, more space better transmission loss (6dB per 3') But for walls is't a luxery to have much space. You can also, for door space, get closer to the wall in those corners and creat a new corner to fold the wall another 2" from the wall (get it?0 hope this helped.

Question 1 I'd now like to add a 3rd layer of drywall to the wall that adjoins my neighbour's house. I currently have 4" stud filled with rockwool, resilient bar, 1 layer of 12.5mm drywall, 1 layer of 15mm drywall. Should I go for another 12.5 or 15 ? Question 2 The outside wall has an airbrick in it, how shall I deal with this? I think I should keep some ventilation, as it's a basement room. Question 3 I need to seal the fireplace up - we're keeping it in for aesthetics for when we move eventually, but will sealing it cause damp problems - normally fireplaces have an air vent in them even when they've been sealed. Question 4 The window is currently double glazed UPVC. I'd like to add some secondary glazing - have you got any tips on this? I'd prefer not to have to build a window, and I'd like one that opens. Question 5 How do I attach my acoustic treatment to my newly sealed plasterboard ceiling and walls without drilling through them and breaking the seals? And thanks as always! Sam

Ro wrote:

4" looks more than enough to me. Ofcourse, more space better transmission loss (6dB per 3') But for walls is't a luxery to have much space. You can also, for door space, get closer to the wall in those corners and creat a new corner to fold the wall another 2" from the wall (get it?0 hope this helped.

Thanks Ro I've gone for using the studs on their sides to create an average spae of 4", and now neatly filled with rockwool all the best

If I use the vertical 4x2s on their sides ie 4" side against the wall (not touching) there will be a 2" air space at the bottom of the wall and a 6" air space at the top of the wall. If this gives an average air space of 4", will the wall's soundproofing effect be equivalent to that of a wall which has a constant 4" air space? Actually this will give performance closer to the minimum distance; think "weakest link" here. Question 1 I'd now like to add a 3rd layer of drywall to the wall that adjoins my neighbour's house. I currently have 4" stud filled with rockwool, resilient bar, 1 layer of 12.5mm drywall, 1 layer of 15mm drywall. Should I go for another 12.5 or 15 ? I'd add another 15mm layer. Question 2 The outside wall has an airbrick in it, how shall I deal with this? I think I should keep some ventilation, as it's a basement room. Considering merrie auld England's fairly constant moist state and the propensity of brick to like moisture, you're probably right; however, this will raise hell with m-a-m performance (holes in one of your mass layers) Question 3 I need to seal the fireplace up - we're keeping it in for aesthetics for when we move eventually, but will sealing it cause damp problems - normally fireplaces have an air vent in them even when they've been sealed. Do you have a pic of the fireplace in question? You may be able to leave the chimney open (is there a cap on top?) and build something similar to a window plug. Question 4 The window is currently double glazed UPVC. I'd like to add some secondary glazing - have you got any tips on this? I'd prefer not to have to build a window, and I'd like one that opens. Everything is a compromise; if you can find a similar (or identical) window and mount it as far away from the existing one as possible, you'll improve m-a-m performance of the window with the wider air space between panes. Caulking up any weep holes will help isolation, but can cause damp problems. Question 5 How do I attach my acoustic treatment to my newly sealed plasterboard ceiling and walls without drilling through them and breaking the seals? You can't; if you've insulated and used resilient mounts, I'd mount any relatively heavy treatments so the screws penetrate your resilient bars (assuming you still know where they are) and if mounting lighter absorbers, you can just use drywall anchors (the little plastic cones you insert before driving a screw) - if you use the anchors, put a dab of caulk into the hole before inserting the anchor. The insulation inside the wall and the tiny (or non-existent) hole won't be noticeable in isolation. As to the RC question, the USG manual shows an extra RC where sheets of gypsum meet, so each has its own resilient bar to mount to; makes it much easier to mount the gyp to the resilient bars, since they tend to be quite narrow from some manufacturers - something like the attached sketch... Steve (the red lines indicate first layer of gypsum)

Thanks very much for your help, a few more Qs below. How will adding another layer of 15mm drywall compare to adding an additional 2"s air? RE the airbrick, I'm thinking of building some type of airseal that I can open and close ie it's open when the rooms not in use. Fireplace - no pic (can't find my camera at the moment, it's in one of the boxes with all my studio kit) It's a pretty standard fireplace and I think I'll build a plug as you suggest, again with an openable air vent AFIK there's no cap on the chimney, but the stack's lowered and roofed over... Res bar - I've managed to get the board joining on the bars, which was advice from Knauf in the UK. It would certainly have been easier as you suggested though, in retrospect etc! Thanks again Sam

my ceiling has 2 layers of drywall on resilient bar, and I'm thinking of putting 3 layers on one of the end walls, where the room adjoins my neighbours house BUT because the ceiling is on res bar, the gap between my ceiling and the floor above is not sealed from the gap between my stud wall and adjoining brick wall IE air can flow freely through my ceiling space and stud wall space. Does this mean it's not worth adding a 3rd layer onto the wall studs, because the ceiling only has 2 layers? Have I explained this well enough? Thanks very much, I'll post some pics of this room eventually!

here's a response frmo the SOS site, but I'd welcome anyone else's thoughts! (Knightfly are you around sir?): I tend to think it would be a waste of time. Mass law states that when you double the mass of a wall, you increase soundproofing by 6db, although in real world application it's probably slightly less than that. Now consider that: 1. You'd be increasing the mass of the stud wall by only 50%, which in and of itself would gain maybe 2-3db sound reduction. 2. The total isolation of the wall is combination of the effects of each leaf. This is not derived by simply adding the transmission loss of the two leaves, it's more complicated than that, but basically the TL of one leaf is "applied" to that of the other, using a formula, and the final result is somewhat better than that leaf would be on its own, though nothing like both leaves simply added together. So, that 2-3db becomes maybe 1-2db (rough guess - there's a formula around somewhere on the net for calculating this if you really want to). 3. As you say the ceiling (and the rest of the room) will only be two layers anyway, and sound will certainly radiate through the other surfaces into the airgap into your neighbour's wall. It's hard to say here whether just beefing up one wall will do anything at all. So that 1-2db becomes maybe 1db at very best. More likely less.

I tend to agree; unless you can also add a layer to your ceiling (without it falling on you :cry: ) it's not likely to be worth the cost/effort... Steve

thanks Steve No more is going on the ceiling, so I guess I've got some drywall sheets to get rid of! The good news is that it means the end is a little bit nearer now!