Studs on both sides of "inside-out wall"?

Studs on both sides of an "inside out wall" Hello! I have a question regarding construction of an "inside-out wall". My builders say that, due to the angled ceiling and the length of one of the walls in question (5,42 meters), they will not be able to build it lying on the floor and then lift it to its vertical position. They asked me if it would be possible to first place a 2x2 frame (studs), attach the drywall (gypsum) and insulation on them, and then build the rest of the 2x4 studs, gluing it to the drywall. It will be far easier to build, but will it affect sound isolation in a negative way? To clarify: The walls will look like this, from the outside to the inside: Wood finish -> 1 layer of drywall -> 2x8 studs with glasswool ---> 2inch airgap (could be larger) ---> 2x2 studs with insulation -> 2 layers of drywall (could be more) -> 2x4 studs with insulation -> fabric. The inside wall will stand on a fully floated concrete floor. It will not connect to the outer wall (or "lower floor") in any way. I hope this is possible to understand?! Regards, Trond

Two things...wait, three things. 1:Your builder does not know what he is doing in respect to a fully decoupled environment. 2:If you truly have a situation where "The inside wall will stand on a fully floated concrete floor." then you would not be asking this question, since your builder would help you in this respect. And last but more importantly, please read the information from the following link: viewtopic.php?f=2&t=3231 as Mr. Sayers would rather you do more to help yourself then have us pull the information out of you.

Thanx for answering! 1. You are right. My builder(s) does not know much about studio construction. They are doing what they are told in that respect, and I am the one who gives the directions. They seem, however, to be interested in the matter, and tries to comprehend the demands about not puncturing surfaces etc. They have yet to deal with the most critical parts - anyway thats my opinion. 2. Hmm. The situation is ABOUT to exist. As far as I know, this will indeed be a real floating floor. Please adress me if I am mistaken! The floor design has nothing to do with the builders. Again, they are just doing what they are told! 3. aaah. The most important thing. I agree, and I appologize for jumping the gun with a quick question. Here´s the whole tale: I´m somewhere in between planning and constructing a 40 m2 studio. I have decided to go for a combination; having the control room and live room in the same space. The studio is 1/3 of a big building project: one apartment for rent, one studio (on top of that apartment!!) and also a 2. floor to the existing house. Together it makes 170 m2 extra on the existing 100m2. Building a studio on top of a rental appartment is generally a bad idea. (So bad, that the “before you post, you must read and follow these instructions”-says: Please don't tell us you want to float your floor if you are building on an upper level - this is almost always impractical, and ALWAYS will require a LOCAL ENGINEER to verify that it will be safe ) We landed on this because it made it a lot more easy to have our plans accepted by the local building authorities. It had something to do about fire-profing, entrance not being 2 meter up in the air, and the structures “foot-mark” – how they count the total square meters. I will not bore you with the details but it is an explanation concerning the odd choice of putting the studio on the 2. floor. And yes, the local enginees has been here, doing his math. The main structure is finished. That means it looks finished from the outside, but inside there is nothing but the walls. What you see is the studs with insulation in between. (See the "innside studio pic") I am therefore not able to do anything about the over all size of the studio. What I´m dealing with now is how to soundproof my room enough to not disturb the appartment underneath. I mostly work with editing and mastering classical music, with a listening level of 83dB (a standart I got from Bob Katz). How ever, as I am also a jazz piano player, I´m sure there will be a trio-session taking place every now and then. That involves a grand piano, drumset (bassdrum!) and doublebass. It will not reach 115dB, but still be a considerable push in the low frequency range that needs to be dealt with. It is sound downwards that is my main concern. Three of the walls leads out in the open, one leads to my own house. It is not important for me to get it dead silent either inside to outside nor between my house and the studio. A guesstimate here is around 50dB. Downwards, on the other hand, is another matter. Here I want it to be possible to have that trio-session without beeing heard by those who rent. I don´t know, but 70dB is probably more what I need? And I guess someone here will point out that sound doesn´t know what is a floor and what is a wall, so any advise to get the equation right is welcome! My budget is a little hard to "get hold of", as the whole building is eating from the same resources, but i reckon it´s in the ballpark of about 15-20.000$. That includes the floor, the inner leaf + ceiling. I contacted one very respected acousic guy, and he got really concerned about the whole 2. floor aspect. Since we could not have that undone (without the authorities having us tear down the whole building) his advise was to float the floor. Added to that it shall not touch the walls, this is my understanding of a floated floor: “a heavy solid layer suspended on a resilient layer of flexible material above the structural floor of a room. For preference, the floating element should be heavy concrete, although particle board can be used in a less substantial installation”. (http://music-production.audiomasterclas ... PflCqWi31c) Based on that, and the demand from the acoustic guy: this what we are planning to do, already next week: On top of the structural floor, we will put one layer of 50 mm mineral wool plates (is that the correct term?). These are specially designed to hold a heavy concrete floor, and they are made with one harder side (topmost) and one softer side (downmost). The acoustic guy advised me to make a concrete floor on top of these plates “as thick and heavy as possible.” My structural engineer allowed us to make 7 cm of concrete. I´m hoping this is enough to get the resonant frequency low enough to keep the low end from getting away. Both the mineral wool and the concrete will have a 5 cm gap to the existing walls. The structural floor consist of 30 cm "lying studs" with insulation in between + 1 cm of wood "battens" on top of that. There is enough height in the appartment to do even more treatment from the inside. (Drywall has yet to be fittet, but is a part of the plan.) The total distance from appartment ceiling to studio floor is 44,5 cm, 16 mm drywall included. Speaking of walls: I´m planning a two leaf system, incorporating an inside-out wall to get good sound isolation and treat the room in one go. My outer walls vary in thickness, from 20 cm to 27 cm. They all have drywall (only 9mm!) outermost, then studs with insulation. I´m aiming for the standard air-gap (if such exist?) of 10 cm between the inner side of the outer wall and the drywall layers on the inside-out wall, as described here on the site. (I could do more, if it is needed!) When I explained how the inside-out wall is build, and the builders got concerned about lifting the heavy wall up and allign it to the angeled ceiling. (12 degrees). They asked if it would be possible to build it in a slightly other way. And this is where my question comes in. 1. will 5cmx5cm (2x2 inch) studs WITHIN the "airgap" harm my attempt to create good sound isolation? John Sayers original design uses 5 cm of insulation, so the studs will not build any more into the airgap than the insulation originally do. But they will of course act in a different way. This structural behavior I cannot predict, and I therefore ask the question here. Look at my attached drawings to see more details. I hope that this post has more useful information than the previous, and please don´t hesitate if there are other things that are important! Trond

Rather than an inside out wall, I would ask why you would not install the mass(sheetrock ) to the interior side of the framing which will increase the air gap which will aid in pushing the transmission loss down. You could build an inside out wall and move the assembly further into the room but there is a cost and the cost is you have the distance from the back of the stud to the front of the stud that can be incorporated into the MSM of the system. John's inside out wall is excellent in smaller places but does come with a low frequency loss due to the proximity of the hard boundaries being close one to the other resulting in a small air space (the "S"pring in mass spring mass). Get the hard boundaries as far away from each other as possible. That said, your decoupled floor isn't going to achieve 20Hz or below but if it is sanctioned it is better than many of the things that you could have done :) Your interior wall framing needs to rest ON this interior slab, not outside or in the airspace. What you are still trying to do is decouple the interior room from the exterior room. Everything you do with a fully decoupled or mass/spring mass environment has to be the same from the floor to the walls to the ceiling to everything including the HVAC, etc. You are building a bubble inside of a structure.

why not tell your contractor to build the wall in sections and add a continuous top plate after. That's what we do when it's a long wall.

Gentlemen. Thank you again for answering. It was particularly nice to see Jon´s signature here as well! I feel happy just thinking about the quality of this forum!! After reading your advice, I´m left with three loose ends. Brien. You suggest that I build a normal MSM-wall instead, to get a greater distance between the hard surfaces of the wall. I have been getting used to the idea of building an inside out wall for so long, that it feels like going back to square one not to do so. My basic treatment plan needs to be redesigned!

You could build an inside out wall and move the assembly further into the room but there is a cost and the cost is you have the distance from the back of the stud to the front of the stud that can be incorporated into the MSM of the system.

Does this mean that I could build the wall in the slightly odd way my contractor proposed, and the only downside would be lack of distance between the sheetrock, resulting in a decreased ability to isolate sound, especially in the low frequencies?

That said, your decoupled floor isn't going to achieve 20Hz or below but if it is sanctioned it is better than many of the things that you could have done

I´m glad it´s not a disaster! How low do you think it will go?

Your interior wall framing needs to rest ON this interior slab, not outside or in the airspace.

That’s indeed the plan. Everything that has to do with the innermost wall will be standing on the floated floor. It will be totally decoupled from the exterior room.

why not tell your contractor to build the wall in sections and add a continuous top plate after.

I certainly could! I may be a sissy here, but I feel that building/constructing things THE RIGHT WAY, is essential, and if my contractor is unsure of the procedure, I kind of hesitate having him do it that way. The loose ends: (where question number two seems the most important..) 1. Is the inside out wall doable, with respected results, even if I put the studs both sides? 2. Would you rather advise me to build the wall properly? How then, would I go about building extra treatment (slot-wall?)? Is there any danger of creating a 3-leaf wall? How should I attach the resonators/absorbers to the drywall without puncturing it? 3. If I build the wall in sections, what´s the trick of sealing the two parts together, air tight? All the best, Trond

If I build the wall in sections, what´s the trick of sealing the two parts together, air tight?

No trick - just seal it as you go.

Like John is saying, you can do it in stages, you should seal every connection and I would use fasteners at every connection(where the studs meet). If there is a trick, it would be to use acoustical caulk at the edges of the panels applied before the next panel is erected. Best case would be to apply the caulk to both panels, but use your best judgement as to is this going to seal the most, etc. "Brien. You suggest that I build a normal MSM-wall instead, to get a greater distance between the hard surfaces of the wall. I have been getting used to the idea of building an inside out wall for so long, that it feels like going back to square one not to do so. My basic treatment plan needs to be redesigned!" Let me say this about that. All I was suggesting is moving the hard boundary to a different position...simple as that. The gained air space improves the TL, again, simple as that. There would be no need to start from square one. You develop the interior massed boundary and you treat it on the interior side. Which is exactly what the inside out wall does...same thing, different approach. If I were you...stay on the track you are on, it will work since you are getting a great air space, I'm just a freak about getting more :) And you have a trusted design in John's work, and trusted designs are difficult to verify these days. Thank you John Sayers,

Hi everyone! Thanks for the answers I´ve gotten so far! I took me a while, and a TON of reading inside of this amazing forum, but now I finally understand that the ”slightly odd” procedure, is simply a combination of an insideout-wall and a normal wall. Kind of.. I have abandoned that idea, and decided to go for a straight two-leaf solution, treating the room afterwards. This has led me forward in the design/buliding process, and I have of course met some new questions. I have already posted the intended floorplan in this thread. That very floorplan is up for revisiontogether with a question regarding a ”fully absorbant ceiling”, and I kindly seek any good advise and opinions on the following: I think that I will leave the flushmouning route. The two reasons for it is 1. to lower the cost/buildingeffort 2. My speakers are Dynaudio bm15A and according to this thread viewtopic.php?f=12&t=168&view=next they do not benefit from flushmounting. This made me design the controlroom area again, and I ended up with two alternatives. (See the pictures) I do believe that alternative 2 would be the best. The reason I included alternative number one is 1. The angeled wall makes the two glass sufaces inside the booth unparallell. 2. The angeled wall is ”prepared for the future” if I shoul decide to build the 6 deg. angeled walls later, as in the original floor plan. Now for the ”fully absorbant ceiling” question: At bobgolds.com, I found this string of data: PRODUCT THICKNESS MOUNTING DENSITY 125HZ 250HZ 500HZ 1000HZ 2000HZ 4000HZ NRC 703, plain 4" (102mm) on wall 3.0 pcf (48 kg/m3) 0.84 1.24 1.24 1.08 1.00 0.97 1.15 (I could not get the layout right, sorry! It looked goog in the text edit window..) This seemes to be the best overall damping through the spectrum. Am I rigth in assuming that to cover my entire ceilind with this would take me a long way towards achieving the so-called fully absorbant ceiling? To sum up, my questions are: 1. Which of the floor plan alternatives would you choose? 2. What alterations would you make? 3. What would be essential to remember (NOT) to do? 4. Will 4” of OC 703 do it for me, regarding the ceiling? Feel free to comment on every aspect that you wish! All the best, Trond