Benefits to insulating in a wall beyond isolation?

Hello all- I'm an avid reader of this forum but a new poster as I, along with my 15 and 13 year old boys, am embarking on a small project studio for us to "play" in in our home in the Minneapolis suburb of Dayton. I have never considered myself an engineer, but am a musician and have managed and owned studios in the past, and I've done some basic buildout. Both of my boys are aspiring musicians, and my 15 year old has taken a strong interest in recording, to the delight of his father. Currently, the studio space we are working on is in our basement, directly below the family room. Thankfully, with the exception of the ceiling, the entire room is surrounded by concrete block, so sound isolation of the walls is of little concern. I've completed framing out the space, and have installed R19 Ultratouch denim insulation between the ceiling joists with one layer of 5/8" sheetrock installed on the ceiling only. I plan another layer with Greenglue and have caulked all seams using the methods described in this forum. My question is this...the walls haven't yet been sheetrocked, and 3 of the 4 walls of the studio are below grade concrete block with nothing but dirt on the other side. The 4th wall is concrete block with just a door opening, and that wall is the control room of the studio, so incoming or outgoing noise here is not going to be a serious issue. I've framed in 2x4's around the perimeter of the entire space and plan to sheetrock all walls but before I do, considering isolation is not an issue, should I still install insulation within the framing of these walls that abut the concrete block? If I do, will the insulation provide me any acoustic benefits in the isolation space or control room, or would I just be wasting money? I've scoured this forum for an answer to this question but every post I've come across seems to concern isolation, not simply any acoustic benefits of installing insulation in walls. Will insulating these walls help absorb low end? Any other benefits? If so, what type of insulation would you recommend? Any advice here would be greatly appreciated. I'll likely have further questions, especially concerning acoustic treatments, in the near future. I'm currently working on a Sketchup of the space to share when that time comes. Thanks! Eric

If isolation isn't a concern then you do not need framing, period :) Spend the saved money on RC or hat track and clips to separate the above live area and your soon to be loud area, you'll thank me later. Although it reads like you have installed the framing. So what does this framing do if isolation is not the goal? In any event, you would be doing yourself a favor to include typical fluffy insulation in these newly framed walls just to help dampen the sheetrock panels, if for no other reason.

I agree with Brien. If there is no need for isolation, then I don't understand the purpose of the walls. Is that maybe just to change the dimensions of the room to a better ratio? Or is there another purpose that you didn't mention? Either way, if you do put drywall on that framing, you will still have created a tuned MSM system, and it will still resonate at some frequency. The frequency depends mainly on the surface density of the drywall and the depth of the cavity, and it may or may not be a frequency that is useful to you, for treating the room. Basically, you will have a room surrounded by tuned panel traps. If they are tuned low enough then they probably won't have too much effect on the room acoustics. So the question is: what frequency will they be tuned to, and is that useful for treating your modal response? You could vary the cavity depths and panel masses to treat several frequencies, if you wanted to get fancy, but that might not be worthwhile. But to answer your question: If you do not put insulation in the cavity, then the internal resonances in the cavity will not be damped. You'll have a panel trap that doesn't trap very well: it will just vibrate. It will still remove some energy from the room at that frequency, of course, but at the same time it will probably also cause some ringing, which isn't a good thing. So I'd say that you still need insulation in the cavity to damp the resonance, even if you don't need isolation. Also, please read the forum rules for posting (click here). You seem to be missing a couple of things! :) So I guess the conclusion is that if you don't need isolation and don't need to change the room dimensions, you should probably take out that framing, but if you do need to change room dimensions, then fill the gaps with insulation, as for any other tuned device. Another option you might want to consider: use the framing to turn those walls into slot walls, and for other types of treatment. - Stuart -

Sincere thanks gents! I greatly appreciate the advice! I figured there was more to it than isolation. And to answer your question, SOME of the framing I've installed is to change the room dimensions, at least in the control room. As far as the perimeter walls, there was already styrofoam, plastic and some 2x2's already installed, so rather than try to tear everything out and figure out how to finish the bare concrete block, it made more sense to install the framing. This also has made it easier to run electrical wiring and install some wall sconces as I'm trying to make as few holes in the ceiling as possible. And I worked on my Sketchup (tried to attach but I believe it is too large) and have at least a general yet dimensionally accurate rendition of the space. The raw space 22' 4" x 12' 6" with a ceiling height of just 7' 6.5". The walls in the Sketchup rendition are solid, but like I said, at this point they are just studs. And the permiter framing is not shown, although it's basically 16 on center. As you can see, I splayed the walls of the control room, and framed in a small sound lock between that and the iso space. I plan on installing a window as shown but don't know the exact dimensions of this yet and haven't finished framing in the opening. As for the rest of the room, like I said, the perimeter is studs in front of the concrete block, with one exception. I haven't yet framed in the back wall of the control room as I'm still contemplating a design for this. Here are a couple of shots from the Sketchup: That said, I do need to finish the walls and am still considering my options. I'm interested in investigating the idea of slot walls and open to any and all suggestions on finishing these walls without breaking the bank. I'd like to keep the remainder of the buildout (not including floor covering or treatments) under the $1000 mark. Can't thank you enough. MUCH appreciation. Best, Eric

And I worked on my Sketchup (tried to attach but I believe it is too large)

SketchUp has this annoying habit: when you delete something, it does not actually remove it from the file! It just stays there, in limbo, forever. Hidden, but still there. To actually get rid of all the accumulated garbage, you have to "purge" the file. Open the "model info" window, go to the "statistics" tab, and click on "purge unused". Then save the file. It should be much smaller now, as it will no longer have the junk.

As you can see, I splayed the walls of the control room, and framed in a small sound lock between that and the iso space.

How much did you splay the walls? How many degrees? Also, what is the purpose of the "sound lock"? I can't see that it will have any effect at all, since the rooms are only separated by a single stud wall. The isolation between the rooms es defined by the wall, not the sound lock. Regardless of how good the sound lock is, it is the wall that sets how much isolation you get between the rooms. It is just wasting space, and serving no useful purpose at all. Get rid of it.

I plan on installing a window as shown but don't know the exact dimensions of this yet and haven't finished framing in the opening.

How is the dividing wall between the two rooms built? You mention "stud framing", but you didn't say if it is single stud, staggered stud, or double stud.

As far as the perimeter walls, there was already styrofoam, plastic and some 2x2's already installed, so rather than try to tear everything out and figure out how to finish the bare concrete block, it made more sense to install the framing. This also has made it easier to run electrical wiring and install some wall sconces as I'm trying to make as few holes in the ceiling as possible.

Fair enough, but do recognize that by putting any hard, massive surface on those studs, you will be creating a resonant cavity behind it, and that will affect the room acoustics in one way or another. So it has to be done correctly, not at random. Also, the Styrofoam is useless, acoustically, so you might as well take that out now. It will do nothing at all to damp resonance in the cavity, and takes up the space that you need for proper insulation, so just pull it out and dump it in the trash.

I'm interested in investigating the idea of slot walls and open to any and all suggestions on finishing these walls without breaking the bank.

Slot walls sound like a really smart idea. But Styrofoam is just as useless for slot walls as it is for tuned MSM walls, so it has to go. Also, you need access to the actual concrete behind the Styrofoam in order to seal it properly, which is yet another reason why the Styrofoam has to go. In order for the slot walls to work, the wall has to be sealed air-tight, so you need to coat it with something that will accomplish that. If it is in good condition, and has no major cracks, then a simple coat of paint might be enough. But if it is poorly finished, then a coat of mortar/stucco/plaster would be the solution, followed by paint. Since a slot wall is basically a Helmholtz resonator, the cavity does need to be totally sealed. very important. - Stuart -

SketchUp has this annoying habit: when you delete something, it does not actually remove it from the file! It just stays there, in limbo, forever. Hidden, but still there. To actually get rid of all the accumulated garbage, you have to "purge" the file. Open the "model info" window, go to the "statistics" tab, and click on "purge unused". Then save the file. It should be much smaller now, as it will no longer have the junk.

Thanks. I believe that worked. File attached(?).

How much did you splay the walls? How many degrees?

The angle was 1 inch per foot, or about 5 degrees.

Also, what is the purpose of the "sound lock"? I can't see that it will have any effect at all, since the rooms are only separated by a single stud wall. The isolation between the rooms es defined by the wall, not the sound lock. Regardless of how good the sound lock is, it is the wall that sets how much isolation you get between the rooms. It is just wasting space, and serving no useful purpose at all. Get rid of it.

Call it a sound lock, or vocal booth, or amp room; but I do want the booth available for vo or vocal tracking. Besides, in the last two weeks since I posted this I've completed the majority of the sheetrocking. See below.

How is the dividing wall between the two rooms built? You mention "stud framing", but you didn't say if it is single stud, staggered stud, or double stud.

The dividing wall is only partially completed. This will be my next project over the next couple of days. The portion of the wall that is completed was done with staggered studs, which I plan to continue with the rest of the construction.

Fair enough, but do recognize that by putting any hard, massive surface on those studs, you will be creating a resonant cavity behind it, and that will affect the room acoustics in one way or another. So it has to be done correctly, not at random. Also, the Styrofoam is useless, acoustically, so you might as well take that out now. It will do nothing at all to damp resonance in the cavity, and takes up the space that you need for proper insulation, so just pull it out and dump it in the trash.

This was the reason for my initial post...to see if I should use insulation in these wall cavities. For what it's worth, most of the styrofoam was covered in sheetrock, and the framing is in front of all of this, so the cavity is wide open. Since I believe it is code in these parts, I thought it best to leave it there. And for better or for worse, in the last two weeks since I posted I've been busy, and completed the vast majority of the sheetrocking. Please keep reading.

Slot walls sound like a really smart idea. But Styrofoam is just as useless for slot walls as it is for tuned MSM walls, so it has to go. Also, you need access to the actual concrete behind the Styrofoam in order to seal it properly, which is yet another reason why the Styrofoam has to go. In order for the slot walls to work, the wall has to be sealed air-tight, so you need to coat it with something that will accomplish that. If it is in good condition, and has no major cracks, then a simple coat of paint might be enough. But if it is poorly finished, then a coat of mortar/stucco/plaster would be the solution, followed by paint. Since a slot wall is basically a Helmholtz resonator, the cavity does need to be totally sealed. very important.

Ok, so here's the update, and I apologize ahead of time for not being entirely clear in my description(s). I'll try to be more so here forward... Before I started, (referring to the top Sketchup screenshot above) the upper and right concrete block walls of the room were finished with a rigid foam insulation, plastic, and then a layer of sheetrock. Like I said above, I believe the rigid styrofoam and plastic is code in these parts for any exterior concrete block wall, which at least portions of these are. So as I said, to finish these walls and in order to run electrical, I framed in 2x4's in front of them. I've since installed the fluffy pink insulation and covered the entire isolation space, the sound lock/vox booth and the control room's left wall (with the entrance door) with 5/8 inch sheetrock. I've been using soundproofing sealant on all of the seams between ceilings and walls and between all layers of sheetrock so it should all be airtight. My next step is to finish the dividing wall. I plan to start on that today. That said, since I last heard from you I've come a long way, and unless there are any obvious fatal flaws in my design, I'm pressing forward with the sound lock/vocal booth intact. It is not at all that I don't respect and appreciate you advice on this, it's just that I'm too far along to go backwards. On that note, before I started construction I did sit down for a coffee with an acoustician who I know, whose advice to me was to build it out as I had planned and then worry about treatments once the room is done, which was my plan. This post was originally meant to answer a simple question ("Should I put insulation in my walls if I don't need to worry about isolation?") but, of course, it's now making me wish I had been working with you from the beginning Stuart. Can't thank you enough for your time. If I have any reason to stop what I'm working on right now, please don't hesitate to post that. Otherwise, if you think I can work with what I have, I sure would appreciate your advice from here forward, especially in the areas of acoustic treatments, and I still have to design and build the back wall of the control room. Best, Eric

" For what it's worth, most of the styrofoam was covered in sheetrock, and the framing is in front of all of this, so the cavity is wide open. Since I believe it is code in these parts, I thought it best to leave it there." The code part is to cover the Styrofoam since it is highly flammable and spreads quickly with a toxic smoke. It is part of your thermal environment to keep the basement warmer. Problem is that basically your existing basement walls that have styrofoam on them covered with sheetrock will produce a three leaf panel resulting in reduced transmission loss once you construct and sheath another hard boundary in front of them.

Ok, so I can still relatively easily remove the stryofoam that is installed in the front of the control room. I'll start on that tonight, which will leave just the concrete block. That said, I am prepared to sheetrock the walls of the control room space, so back to my original question. Before I put up the sheetrock, it would be best to install standard fluffy insulation in the cavities, right? Before I go any further, any other considerations before I do this? And also, the rear wall of the control room has been untouched, but the concrete block is currently covered with "bildrite" fiberboard (the stuff they cover new homes with before they put up housewrap and siding). Is is safe to assume that this should be removed as well? I've been holding back on touching this wall as I've been waiting to seek out some advice here as to what combination of absorption/diffusion would help for my control room acoustics. I plan to build superchunks for all corners, but am uncertain on how to treat the rest of the rear wall, as well as the rest of the room. Any help you can offer would be appreciated.

I've updated my SketchUp file with more detail and to reflect my progress. Attached is a copy, and below are a couple of screenshots. I've completed sheetrocking of the live room and the sound lock/vocal booth/wasted space (whatever you want to call it) as well as the control room side of the dividing wall. The stryofoam is being ripped out of the control room wall, but the fiberboard still does cover the concrete block on the rear wall. Does this have to go? I'd like to push forward. Any advice you can offer would be great. Thanks very much, Eric

I've updated my SketchUp file with more detail

I don't see the detail of how you plan to do the framing for the wall between the control room and live room / booth. From the SKP it looks like that wall is attached to the outer-leaf (concrete block) walls at both ends, but I guess that must be a mistake in the file. The booth wall with the window in it also seems to be attached to the outer leaf, and that too must be a mistake in the file. Perhaps you could update the SKP with those details, to make sure that those have been planned correctly. - Stuart -

I've added the detail including the framing for the dividing wall. The walls are not attached to the concrete block, however they are to the ceiling joists. Below is a screenshot, and the updated skp file is attached. Thanks Stuart.

"Ok, so I can still relatively easily remove the stryofoam that is installed in the front of the control room. I'll start on that tonight, which will leave just the concrete block. That said, I am prepared to sheetrock the walls of the control room space, so back to my original question." No sir, back to the question of what shape is the concrete wall in after you remove the styrofoam and sheetrock. Once you do this extraction you can potentially create paths from the exterior to the interior since we have to assume that the fluted or hard cut nails that supported the wood materials to the concrete have left a hole. The sheetrock was not glued to the styrofoam, there are battens, 1 X4 or 1 X2 treated wood strips that the sheetrock is fixed to and the styrofoam has been installed inbetween the the batten layout. Or some configuration similar. But the block has to be sealed, not filled, but sealed in such a way as to allow condensation transport from either side of the room.

The concrete behind the stryofoam is in excellent condition, as it is throughout the basement. There are 2 battens attached strictly to the ceiling and floor with the stryofoam loosely wedged between. The sheetrock was attached to the battens. That said, can you please elaborate on your latest post? I'm hoping this has to do with preventing condensation and potential mold issues. Installing fluffy insulation against concrete block as I'm sure you know is not ideal. Stuart mentioned that coating this with a coat of paint will suffice if the block is in good condition, but this will not entirely block moisture unless it is a waterproofing paint. You said:

...the block has to be sealed, not filled, but sealed in such a way as to allow condensation transport from either side of the room.

I'm not familiar with what you mean by "condensation transport" and don't understand what you mean by "either side of the room". Is the intention here to create an appropriate resonator? Seal the concrete from leakage? Both? It might be helpful here if I had a better idea of where you are headed. Maybe it's me. Regards and thank you again. Eric

Stuart mentioned that coating this with a coat of paint will suffice if the block is in good condition,

Yes, but that is for acoustic reasons, not related to moisture. The surface needs to be sealed simply because brick and concrete are porous, and you need a hermetic seal to maximize isolation. In simpler terms, Brien is talking about "waterproofing" while I was talking about "soundproofing". - Stuart -

So in theory a product such as this should work to both soundproof and waterproof in my application. http://www.ugl.com/drylokMasonry/masonryWaterproofer/extreme.php Here is a description: DRYLOK® Extreme Latex-Base Masonry Waterproofer Ideal for interior, exterior, above or below grade masonry walls, basement walls, retaining walls, foundations... Flexible Encapsulated Polymer used for the ultimate in waterproof protection. Specially formulated to resist mildew growth on the paint film. Stops 12 psi, that’s greater than a wall of water 26 feet high! Passes ASTM D-7088 Resistance to Hydrostatic Pressure an ASTM D-6904 Resistance to Wind Driven Rain. Would you agree?

The trick, etrelstad, is to build a room by conventional means, taking all the known ramifications of physics as it applies to a structure, and to do this in such a way as to relieve yourself of the obligation of being mindful of the thermal environment you just created. Tricky statement I know. Acoustics is a word...but it applies to everything in different ways in a thermal environment and the two often share responsibility for the benefits of either reduction in sound or higher thermal environment. Take for example, the decoupled wall assembly we so highly prize. Not only is that an acoustical break, it is also a thermal break. You only need to look at a double insulated window or a thermal coffee mug to understand this principle. We have people that sell us acoustics and we have people that sell us thermal ...the two are the same in respect to how does it function. It functions because of the break we discuss as the path vibration rides on, but this is also the path that thermal exchange rides on. So in answer to your question, yes I would paint it since this is a good vapor retarder. What I would not do is to try to stop the migration of condensation, which is what I had said up topic.

Thank you for the detail. This has definitely been a learning experience already. I will go ahead and apply a coat of paint to the concrete block, and would welcome any expertise as to my next step. Very much appreciated.

Thank you again gents. Your time is greatly appreciated. We finished painting the concrete block and I'm ready to proceed with the next step, but am concerned there is more I need to consider. Stuart, you commented...

I don't see the detail of how you plan to do the framing for the wall between the control room and live room / booth.

and

The booth wall with the window in it also seems to be attached to the outer leaf, and that too must be a mistake in the file.

...to which I responded with a more detailed screenshot and Sketchup of the framing I've installed up topic. Brein, you suggested painting the concrete block before installing the insulation within the framing of the control room and then the gypsum board, which is now done. Keeping in mind that isolation is not much of an issue in this build, if there are any other considerations before I complete the walls in the control room I'd greatly appreciate any advice. Best, Eric

Gents. I'm at a bit of a standstill. I'm planning to work on the studio most of the day tomorrow, and am hoping to work on the control room walls. As I mentioned, I painted the concrete block, and since, I've completely sealed the cavity. I've been planning to sheetrock the control room walls, but if I'm headed in the wrong direction and there is a better approach, OR, if I'm forgetting anything before I do go ahead with my original plan (install insulation within the framing surrounding the control room and sheetrock over that) please let me know. Thanks so much, Eric

Before I finish the walls of the control room, I have a couple of questions. Previously it was mentioned that slot walls could help, and I've been reading up on them. I worked up a Sketchup design for the left side wall of the control room you see below (I hope you can read them and they make sense). Like I said, the concrete block in the control room is painted, and I've completely sealed the space behind the studs on all sides, top and bottom. Question is...is there benefit (and is it worth it) to build a slot wall on that left side, especially considering I don't have the option of doing the same on the opposite side of the control room? Would it be better to have similar materials on both sides, or would a slot wall on the left side only help? Also, if I did the slot wall, as the studs are not attached to the concrete block, I would need to seal the space indicated, as there is airspace that wraps around to the front wall, correct? I have a bunch of wiring and outlets on the front wall so this wall I am assuming would be best just to seal off and sheetrock? And also, I'd want to install Owens 703 or 705 against the concrete block for it to be effective? Then there's the question of how wide I should make the slots? Am I on the right track here, or is this just a waste of time and not worth the extra $$$? Thanks again and again. Eric

Question is...is there benefit (and is it worth it) to build a slot wall on that left side, especially considering I don't have the option of doing the same on the opposite side of the control room? Would it be better to have similar materials on both sides, or would a slot wall on the left side only help?

If you are talking about the front half of the room (where the speakers and desk are), then no, it would not be a good idea. The front half of the room must be absolutely symmetrical, so that both speakers sound exactly the same at your ears. If this is in the back of the room, then it might be useful. provided that you don't take up space with it that would be better occupied for bass trapping. - Stuart -

Makes sense. Thanks Stuart. I'll just insulate with typical fluffy insulation between the studs as originally planned and treat within the room when I finish. I haven't started on the back wall, and would greatly appreciate some help on that when the time comes. I'll post some of my ideas when ready. Best, Eric