Ceiling detail

Firstly: Thank you for an amazing resource, I felt I knew a lot but I guess it's the stuff you didn't know you didn't know that suddenly highlights how much there will always be to know! I have just bought a house that has a basement/ garage area with almost the same dimensions as John's excellent small_studio.skp . I'm planning to pretty much follow that design. The only variant is my ceiling height which limits the amount of construction I can fit in for headroom. The ceiling in question is actually the floor to two bedrooms. The bedroom floors are uncarpeted (and for allergy reasons will remain so), they are some kind of hardwood strips attached to joists. The joists are 200mm deep and are all around 350mm apart. These joists in turn rest on steel beams at 2 meter intervals. From the studio floor to the underside of the ceiling it is around 2400mm, fine I guess but as soon as I were to add an additional leaf and absorption I will quickly eat up my headroom. If I am under the floor (intended studio) and someone walks across or does anything I can hear it below as if the ceiling wasn't there. Clearly my biggest issue is getting as much isolation here. The walls are all under ground and we have no neighbors close enough to warrant any other issues. From reading the site it appears that a two leaf system will be best but I have a few questions regarding the implementation. As for cost I'm hoping to get away with the cost of timber, plaster board and insulation. My focus will be on the "live room" area first, I will tackle the control room if the live room is reasonably successful. Q1: I assume the existing floor above me, including the joists and steel bars can be considered to be one leaf. If so, what would be the best approach to bulk up that leaf. Could I attach plaster board directly to the underside of the floor but between the joists? Q2; I want to create a second leaf for the ceiling but obviously I can't attach it to the joists or steel beams as I will effectively couple both surfaces and render the 2 leaf idea useless. Can I hang the new joists from the new walls with the new joists going in between the existing joists (not touching the underside of the floor) and attaching 2 layers of plaster board to the new joists. The air gap will be just over 200mm albeit with lots of joists inside - maybe even loosly pack insulation between the leafs. (This new ceiling will incorporate some angled areas too) Q3; If the new ceiling leaf joists are mounted on the new wall then will the new ceiling and walls be coupled, at least at the joist hangars. If so is this bad or is there a better way to do it? Thank you in advance for any response. I would imagine this is a fairly common problem. If I have missed a post about this kindly kick me towards it. Koos Turenhout

Hey Koos, and welcome! (South African name, by the sounds of it? I used to live there, many years ago....)

Q1: I assume the existing floor above me, including the joists and steel bars can be considered to be one leaf. If so, what would be the best approach to bulk up that leaf. Could I attach plaster board directly to the underside of the floor but between the joists?

Yup! That's exactly what is recommended here. It's called "beefing up" the floor. The idea is just as you stated it: Cut strips of 5/8" drywall (plaster board) to fit the gaps between the joists, hold them in place with cleats, and seal around the edges carefully with acoustic caulk. Add more than one layer if you can, but check first with a structural engineer to make sure that your floor can take the extra load.

Q2; I want to create a second leaf for the ceiling but obviously I can't attach it to the joists or steel beams as I will effectively couple both surfaces and render the 2 leaf idea useless.

Well, you CAN attach it, provided that you use something to decouple the drywall form the joists, such as resilient channel, or RSIC clips and hat channel, assuming that those are available where you live. That is one possibility, but of course it isn't as good as a building totally separate fully decoupled inner leaf.

Can I hang the new joists from the new walls with the new joists

What new walls? I guess you mean that you plan on building proper inner leaf walls around your room, and hanging your new joists from those walls alone? If so, then the answer is yes! Absolutely! That is the best way to go. Beef up the outer leaf where necessary, and build a totally separate, decoupled inner leaf.

Can I hang the new joists from the new walls with the new joists going in between the existing joists (not touching the underside of the floor) and attaching 2 layers of plaster board to the new joists

Yeah, you can do that. Its one way of doing it. another way is to build the new ceiling "inside out", meaning that you build it with the drywall on TOP of the joists, instead of underneath. It's a bit more complex to build, but gives you the huge advantage of not using up any headroom! The space between the joists is now inside your room (as opposed to being inside the ceiling cavity), so you can use that entire space for acoustic treatment. The usual recommendation here is to fill the entire joist space gap with mineral wool or fiberglass insulation, and stretch some type of acoustic cloth across the joists, under the insulation, for aesthetics. In that case, keep your floor hard and reflective (concrete, laminate wood, etc.).

Q3; If the new ceiling leaf joists are mounted on the new wall then will the new ceiling and walls be coupled, at least at the joist hangars. If so is this bad or is there a better way to do it?

Yep! This is good. The iea is to build it as a "room within a room", where the new walls sit on the floor, and the new ceiling sits on the new walls. Apart from the floor, there is NOTHING that connects the existing leaf to the new inner leaf: They are totally separate structures. Good luck with your build! PS. If you don't already have it, get Rod Gervais's book. It's the best there is. Kind of like the studio builders' Bible, if you will. - Stuart -

Thank you Soundman. It's actually a Dutch name but I did live in Cape Town for 18 years - ironic what with all the "Dutchmen" there! Your advice is great. I'm just researching options for resilient chanels over here, I see Auralex and the RSIC- VClips systems look good. Any Kiwi's here that know of a localy available product for resilient chanels? Best regards, Koos.

I'm a Kiwi - born in Auckland NZ :) left in 1966 ;) as you have bedrooms above I'd suggest you avoid the Resilient channel method and completely decouple from the upstairs. - beef up the upper floor as Stuart suggested but build a new ceiling below the exisiting one. any chance of a plan of your space with dimensions and preferably some pictures?

Thanks John; sweet as. (As they say in NZ) I'm still researching until I'm confident I understand every aspect. In terms of size it is virtually identical to your small_studio.skp but with a max floor to ceiling height of 2400mm, hence my need to maximize headroom and not loose it to additional joists. As soon as I have moved out all the existing shelving and junk I will post a pic or two of the existing space. Just moved in so my wife has other priorities right now! But it doesn't stop me thinking through all the details until I get the time to get going withthe build. Ta. Koos.

So, I've been pondering what to do and looking around for resilient chanel solutions in NZ. I found this product that one attaches below the joists which allows you to then add in your "hat?" or new rail on which you attach your plaster board. This looks neat as it decouples because of the grommets. It seems too good to be true - any comments?If this is a reasonable solution then my logic goes on to consider that I could use rubber grommets to decouple almost any components, even placing a grommet behind each screw that attaches plaster board to the frame. Anyways, the "quiet-clip" idea will certainly allow me to incorporate a second leaf but attached to the existing joists, and take up minimal headroom in my space. Any comments? Thanks. Koos.

Hoi Koos, welkom bij JLS :)

Hi Koos, It looks like I opened a can of worm by mentioning RC! It's a second-best solution, and one that you really don't want to use unless you have no other choice. Like John said: Go with the full "room-within-a-room" construction. There are several reasons why RC might not work for you, but the two biggies that I see: Those curious clips that you found are not RSIC clips. Unless there is published scientific data on how they behave acoustically, put out by a reputable independent acoustic lab that did real acoustic tests on them in a real acoustic laboratory, then drop them, turn, and run away from them really fast!!! You don't want them unless they are tried and proven as an acoustic isolation medium. PLaying around with things that look like they "might" work, or because someone said they think they "could" work, is a sure recipe for disaster. Just so you get the idea: In order for any kind of rubber to work as an acoustic isolator (decoupler), it has to be compressed to just the right amount when fully loaded. Normally that means it needs to be compressed by something like 10% to 20%, but that depends on the type of rubber. In order to get the right compression, you need to calculate the total mass load that you will be placing on the rubber, divided by the contact surface area, and you need to compare that with the published specs for the type of rubber. If you compress it too much (too much load), then it "bottoms out" and flanks: it's like there was no rubber, and therefore there is no isolation, no decoupling. If you don't compress it enough (not enough load), then it also doesn't isolate, and doesn't decouple. The only place where it decouples well, is in the range where it is compressed correctly. Any more or less, and it doesn't work effectively. With RSIC clips and RC, all of that has been done already: There are numerous studies on how they work, how much load you can put on them, how much air space you need behind them, etc. It's all been done. You can read the manufacturers specs, and they tell you exactly how many layers of drywall you need, and what spacing you need for the clips or RC, in order to get correct loading, and good isolation. With your clips, you are on your own. You will have to be your own acoustics lab, to figure it out. And the chances of you "lucking out" with your unknown isolators, and getting it just right by pure guessing, are pretty low. Roughly zero, I'd say! Then the second issue is that of structural integrity: You need to beef up your existing floor above you, to complete the outer leaf, and that is going to place an extra load on the existing structure, which may or may not be OK (only a structural engineer can tell you that). But if you use those clips, then you will ALSO add the ADDITIONAL load of the second leaf, hanging from the SAME joists. That will very likely place too much load on the existing structure. Once again, only a structural engineer can tell you, but the chances are it will be overloaded. Bit if you build a "room within a room", then the new inner-leaf walls are supporting the new inner-leaf ceiling, instead of the existing joists, so your load is supported correctly. Like John and I said: RC and RSIC clips are second-best choices anyway: Best choice is a separate, isolated, inside-out stud-framed "room within a room". - Stuart -

Hi Soundman. Thank you for the use of your experience! There are a lot of acoustic details for those clips, I'm going to study them further but it does seem with the specs they give that they will support one layer of 13mm plaster board. I appreciate your point about the loading of the joists too. I'm going to have a serious rethink. The clips idea wouldn't have given me much creativity in creating angled ceilings either, whereas building the second skin I can get more adventurous! Thank again, Koos.

I'm going to study them further but it does seem with the specs they give that they will support one layer of 13mm plaster board.

That isn't very much! A single layer of plaster board isn't enough, and especially if it is only 13mm. That's roughly 1/2", but you need 5/8" (around 16mm), and you need at least two layers of that, which totals 32mm. So you'd need 3 layers of 13 mm to get roughly the same mass as two layers of 18 mm. If those clips will only handle one layer of 13 mm, then you are short by two thirds on the mass you need. (Not only that, but the resonant frequency of 13mm plaster board is higher than that of 16mm, which is not good. You want the resonant frequency to be as low as possible. It would be nice if they made 50mm plaster board! That would be great for studios! But they don't, as far as I know, so just go for the thickest stuff you can possibly get.)

The clips idea wouldn't have given me much creativity in creating angled ceilings either, whereas building the second skin I can get more adventurous!

Yup! Good point.