Ceiling Problem

Hi, I have a build thread but thought I would ask this question separately as its become a bit of an issue that Im not sure how to overcome. The area I am looking to put rehearsal studios into has 9" brick walls, a concrete floor below, but unfortunately a mezzanine floor above - one of the workers downstairs said they could hear someone walking above. This mezzanine is boxed down into my unit (about 6") but given what I can see from the bits that are now exposed it has no insulation or mass as such apart from the floorboards above and the plasterboard my side. This is a massive area, probably around 3,500sqft used by the studios if you include a corridor. So, my problem is that the existing ceiling is a very poor excuse for a leaf, so even with a well constructed studio below I need to address the mass of the mezzanine. As I am running a central corridor with studios on each side, one idea I had was to run joists above the studios from the central corridor wall to the external walls and effectively create a proper second leaf. The corridor walls were supposed to go right up to the ceilings to create a second leaf to the studio wall mass, but runing them to the ceiling now seems pointless if the ceiling is effectively a bit of plasterboard with no mass behind it? I would be really grateful for any opinions on how to approach this issue as its a bit of a show stopper for me at the moment. heres a basic image of the current layout. The studios are in blue. Thanks, Ben

Ben, I would say that you basically have two options here: 1) Open up your ceiling completely, so you have full access to the "floor" above you, and beef that up with plenty of additional mass as well as careful air-tight sealing all over, and also take all your outer-leaf walls fully up to that, once again with careful sealing. This assumes that the existing structure is able to withstand the huge extra mass you'd need to add to it: 3,500 ft2 at, for example, 7 PSF (3 layers of 5/8" drywall, roughly) works out to well over 24,000 pounds of extra mass... :shock: :!: Can the structure up there handle that? Clearly, you cannot answer that yourself: you will need your structural engineer to figure that out for you: It also assumes that you are even allowed to do that: You'd be modifying the structure of the building itself, and your contract very likely does not allow that, if you are sharing the building with others. There's also the issue of insurance: will your insurance cover the liability and risk you take on by doing such a major modification of the building structure? 2) Forget all of the above, and just build a new ceiling over the entire isolate section of your studio, with sufficient mass to provide the isolation you need. Yes, this will be a 3-leaf system, but sometimes that is the only reasonable solution. Yes, a 3-leaf system does potentially reduce isolation in the low end of the spectrum, which you very definitely need to isolate greatly, but there are ways you can compensate for the lost isolation. With this plan, you will still need to put up those 20-something-thousand pounds of mass (and probably much more) in order to build that "middle leaf", but it will be all within "your" area of the building, and likely not subject to the same problems as trying to modify the parts of the building shared by others tenants. And you'll still need your structural engineer to do all the math for you, figuring out how to support that while spanning the distances you need to span, etc. But overall, I suspect this might be the better way to go. And since your isolated space is basically split in two by the central corridor, I suspect that your best bet would be to do two independent isolated areas, one on each side of the central corridor, so that you only need to span that much shorter distances on the sides (less than half the building width), and you'd not need to isolate the corridor at all like this, since it would be outside the isolation area. Save you some money! In other words, you would not need to isolate the full 3,500 ft2 of floor area: only the exact amount that actually needs isolation, which I suspect is a whole lot less! Personally, I'd go with option #2! :) It will need some careful design (way, way more details than what you are showing in your very basic models so far), and it will need major attention to that detail in the HVAC system, which will now be split in tow as well, and still needs to penetrate all of the walls while providing the extreme isolation you need, but overall it looks like the best solution to me, by far. Also the cheapest... :) - Stuart -

Option 2 please Stuart... :D Im hoping this is the kind of thing you mean? I just did one side of the room and put some of the joists up for illustration. The inner room is made from metal stud with mass on one side, the surrounding wall (joist walls) is made from solid concrete blocks, 9" thick and encloses all of the studios on that side. I pressume I dont need to build a specific corridor now as the blockwork is effectively the corridor? So, should these joists hang a course down and mass added underneath or above or both? Im thinking 12" x 2" joists - is that too mcuh? Thanks, Ben

Im hoping this is the kind of thing you mean?

That's the general idea, yes.

I just did one side of the room and put some of the joists up for illustration.

Yup. Hint: In Sketchup, you can make and duplicate things called "components", every easily. Select the six individual faces that form one joists, right-click and select "make component" (with "replace selection" turned on). Now select the component joist, tap the "ctrl" key on your keyboard, and a small "+" sign should appear next to the cursor, indicating that you are going to copy the joists, not move it. Drag cursor over a bit in the direction you want to copy it, just a couple of inches, then left click once. Now type the real distance you want in the "length" box (bottom right corner of screen), such as for example ' 16" ', and hit enter. Now type an asterisk followed by the number of copies you want: for example " *20 ", to make twenty copies. Hit enter.... Bingo! You now have 20 joists spaced 16 inches on center... :)

The inner room is made from metal stud with mass on one side, the surrounding wall (joist walls) is made from solid concrete blocks, 9" thick and encloses all of the studios on that side.

Looks good to me! Another option for your "middle-leaf" ceiling might be "beam and block", which is basically just pre-stressed concrete joists that are specially shaped to take concrete blocks in between them. Like this: http://www.milbank.co.uk/beam-and-block.php That gives you the best possible isolation you could ever hope for, since it retains the high mass of your walls all the way around the enclosure, and also solves the issue of how to get a lot of mass on the "middle-leaf ceiling" easily, fast and at at reasonable cost. Then you build your inner-leaf as you described above, with stud-and-drywall for both the walls and ceilings. With enough mass on those leaves too, and a good air gap, you will get major isolation, both between rooms and certainly to the outside world. Just make sure you leave enough space between the inner-leaf ceiling and the middle-leaf ceiling to fit in all your HVAC ducts and silencer boxes.... :) That's a whole different kettle of fish that you haven't even looked at yet...

I pressume I dont need to build a specific corridor now as the blockwork is effectively the corridor?

Right.

So, should these joists hang a course down and mass added underneath or above or both? Im thinking 12" x 2" joists - is that too mcuh?

If you go with wood joists, instead of the "beam and block" solution, then you could use joist hangers, and put plenty of mass on that middle-leaf ceiling. I'd suggest several layers of MDF plus drywall, perhaps with Green Glue as well, to build it up thick enough to get a really high mass. With a 3-leaf system, you need most of the mass on the middle leaf for optimum isolation. That's why I suggested the "beam and block" approach. Another option would be to just pour a concrete ceiling slab. And one other option again would be brick. - Stuart -

If this reply pops up twice apologies - I spent ages replying and thought Id submitted but cant see it. My wife says I endlessly repeat myself anyway...

Yup. Hint: In Sketchup, you can make and duplicate things called "components", every easily. Select the six individual faces that form one joists, right-click and select "make component" (with "replace selection" turned on). Now select the component joist, tap the "ctrl" key on your keyboard, and a small "+" sign should appear next to the cursor, indicating that you are going to copy the joists, not move it. Drag cursor over a bit in the direction you want to copy it, just a couple of inches, then left click once. Now type the real distance you want in the "length" box (bottom right corner of screen), such as for example ' 16" ', and hit enter. Now type an asterisk followed by the number of copies you want: for example " *20 ", to make twenty copies. Hit enter.... Bingo! You now have 20 joists spaced 16 inches on center... :)

This deserves a Spinal Tap 11/10 - I really need to start working out how to use sketchup properly. I think my basic problem is that I see everything as a rectangle with no eye for aesthetics or detail, so when I put a rectangle down and push/pull it Im in my element and its job done. :o

Another option for your "middle-leaf" ceiling might be "beam and block", which is basically just pre-stressed concrete joists that are specially shaped to take concrete blocks in between them. Like this:

This is perfect and definitely the solution. I have a Q re headroom though. The ceiling has around 12.5' to play with and I can see from imagaes that the builders will need a bit of room to place the blocks into beams? If the studio ceiling height is 8 to 8.5' after mass is applied, the joists walls 10' high will this 1. give enough space for the builders to work with 2. Be an ok height for a rehearsal room (assuming mode is acceptable) I guess in the above scenario there will be at least 12" gap between mass of studio ceiling and the mass of the block and beam - does that look ok? Wall thickness - I jumped in at 9" - to make this manageable for the builders it will have to be 4" blocks laid flat or am I going overkill with thickness of these walls?

HVAC ducts and silencer boxes.... :) That's a whole different kettle of fish that you haven't even looked at yet...

Yeh...dreading this actually. I think the AC will be relatively straightforward (i wish i hadnt typed that) - or at least it is easy to visualise as without some convoluted system whih I can ill-afford the likelihood is that its going to be a multi-split system (we have one with around 10 wall/ceiling units for next to £nothing). The Air exchange is the bit that seems more involved. I have found a potential solution that I intend using in the teaching rooms: For extraction I want to use this residential solution which can handle up to 9 rooms. Using insulated flexi ducting and maybe silencer boxes/inline attenuators I reckon this might work? ...be gentle (see link below) http://www.justfans.co.uk/mev-spider-mechanical-extract-ventilation-unit-p-342.html So I dont suffocate ppl I now need to deal with the ventilation and again I have a solution for the teaching rooms that im hoping will do the trick for the studios. The same Co. do an inline fan that is only 19dB and basically pumps air along a duct. With flexible insulated ducing coming off to each room (no doubt snaking ia silencer boxes and maybe inline attentuators?). They also have a £10 manual throttle that ensures that the air flow is distributed evenly to each room. I guess there may be a need for a second inline fan but they do not seem to think so. I got them to do an air exchange calculation and its around 11 exchanges per hour - I'll double check this myself when I actually understand the calculation :D , but it seems promising Thanks again, Ben

I know the builder will know what to do, but so I can get it clear in my head how does the beam and block sit on/in the wall. I put this component in and it raises Qs over how to incorporate. Edit: Actually, looking at it now am I right in thinking if the block and beam are the right size they just become the last course in the blockwork? more like: Thanks, Ben

Just had a chat with someome re the beam and block. They seem to think that it would be virtually impossible to manage due to the headroom available. I guess we have to get concrete on top of the blocks and we have little room to work with as per my previous post? So, assuming we go back to the joist hangers solution I intend putting 2 x layers of 15mm MDF and 15mm plasterboard under the joists with rockwool filling the joists - caulked to death at every turn. I guess using this method I can take the block wall up 11' and give myself some serious room to play with for hvac etc, so. The studio ceilings can now be 9' and I anticipate c. 12" gap between the inner leaf and the middle leaf mass. In theory does this sound like a plan?

In theory does this sound like a plan?

Well.... In theory, there's the issue of the math. The density of brick is very roughly 2300 kg/m3, so a 9" thick brick wall weighs about 525 kg for every square meter of surface. Drywall, on the other hand, has a density of around 650 kg/m3, so two layers of 15mm will weigh roughly 20 kg for every square meter. In other words, the surface density of your walls would be roughly twenty-six TIMES higher than the surface density of the ceiling. So you'd need about 54 layers of 15mm drywall to get the same mass up there... :shock: :!: Conclusion: theory is not on your side here! There is no point in doing the walls 26 times better than the ceiling, especially when it is the CEILING that needs the most mass, as it is the middle-leaf of a 3-leaf system. In theory, that middle-leaf ceiling should have twice as much mass as each of the other two leaves (or in other words: the mass of the inner leaf and outer leaf combined, should be the same as the mass of the middle leaf). The conclusions that you can draw from this are that either 1) there is no point at all in doing brick walls, when stud-and-drywall will match the same mass as the ceiling. 2) you need a hell of a lot more mass on the ceiling. Those are your two potions. So which way should you go from here? Increase the mass on the ceiling, or reduce the mass on the walls? The only real answer I can give is: "Beats me! I have no idea. Not a clue." Not because I can't figure it out, but simply because I don't have the basic data I need for figuring it out. Once again, it boils down to not having a number: You still don't know what your goal is! You really should settle on the amount of isolation that you need, in terms of how many decibels of transmission loss you want and the lowest frequency you need it at, then work forward from there. Right now, it is all just guess work, with no actually goal in sight. It's like you are saying "I want to get in my car and drive to my destination: please tell me how to get there.", but when people ask you "OK, but where is your destination?"; all you can say is "I'm not sure: some nice place that I'd like to be that isn't here where I am right now!" :shock: :!: I think you get the point. At present, you have no real idea where you are going, or what you are aiming for, other than "It is different from what I have right now". If you settle on a figure, then I can do the math and tell you which of your current two options will get you there, but without a goal, it's better to just toss a coin: regardless of which way it lands, the answer will be equally "right" since there is no "wrong" when you don't have anything to aim for. The tossed coin will give the "right" answer, simply because there is no meaningful question! There are equations for calculating what you want to know, in terms of what density materials you need, and how you should arrange them, but in order for the equations to give a valid answer, you have to feed them valid data! I can plug in a number like "61 dB" or "45 Hz" but I cannot plug in "I'd like some isolation please" and "musical frequencies that the band likes". The equations only work for objective numbers, not subjective feelings. So I really cannot say which option is the best for you! If you only need low to moderate isolation, and are fine with lots of bleed between rooms and to the outside world, then by all means, skip the brick walls and just go with simple stud-and-drywall everywhere. Or if rally DO you need the very high isolation that you would have got from bricks, then you need to figure out a way to get similar mass on the middle-leaf ceiling. There's no way I can give you better advice than that, since I don't know where you are going, or what you are aiming for. If you have no clear destination, then telling you "Drive north" is just as good as "Drive south": both will get you to a destination: it just might not be the one you wanted to arrive at... All I can say is that doing massive 500 kg/m2 walls along flimsy 20 kg/m2 ceilings, makes no sense, acoustically speaking. - Stuart -

All I can say is that doing massive 500 kg/m2 walls along flimsy 20 kg/m2 ceilings, makes no sense, acoustically speaking.

Thanks Stuart that makes sense. Id love to go down the beam and block route but it doesnt seem possible and obviously having block walls and a non block ceiling is as you say....pointless. The isloation requirements have changed based on the poor ceiling so ideally we need the studio ceiling and the middle leave to reduce 115dB down to 50dB. So I would say that we are looking for 65dB reduction, 70dB if possible. The non-numeric descriptive is I want a band to be able to rehearse below in the studio and not be heard at all above the rather pathetic ceiling that currently exists 13' above. Im going to take a dB metre there tomorrow and try and get a figure on what the ceiling offers in terms of separating from below, which I know is a factor but its safe to say its going to bring very little to the party. In terms of frequency ranges Im actually not sure how to answer this. Its standard band rehearsal with bass, drums guitar keys vocal. Is there a way I can give you these figures or is there an obvious figure you can use? Is that the kind of detail you need to calculate the mass required? Thanks, Ben

dB reading: Ok, I managed to get a dB reading today courtessy of a pneumatic drill. Up close and personal 101dB - upstairs directly above with meter close to floor it was 81dB - having said that I would be tempted to say I could feel it more than i could hear it.... but it was loud enough to raise a complaint from above. meter was set to C and slow. The ceiling was actually exposed a little almost directly above the test as builders had ripped a hole in order to ascertain the structure so Im guessing that once patched up and sealed it could be a bit better tthan TL of 20dB but these figures are all i have to work with atm. Exposed Ceiling: I managed to get a hydraulic platform lift up to take a photo of the 18" ceiling void between the plasterboard and the chipbpoard floorboards above. Elecrtricty Monster - now you see why it cant be moved, although we have taken down the walls around it and will rebuild with a lesser footprint. The void you can see against the far wall only exists for a couple of feet - its a trench that runs that whole back wall and is going to be used for storage or some such thing.. Everything else is solid concrete on the floor.