STC rating of Inside out wall construction

Hello, what a great forum this is I am looking for details on inside out wall constructions and could not find any resutls on comparing traditional wall design and inside out constructions. Example normal design: 12mm Board 100mm Stud and Rockwool 50mm Air 100mm Stud and Rockwool 12mm Board Example inside out: 100mm Stud and Rockwool 12mm Board 50mm Air 12mm Board 100mm Stud and Rockwool Thanks Helge

welcome, please update your profile to include your location information. if you check out John's recording manual you can find more information on the inside-out wall composition including the inside wall treatments using slats etc. are you looking for detailed isolation data? you might want to read up on some of the construction threads where folks posted some information on their isolation measurements.

What Glenn said! Plus, 12 mm drywall is too thin. Use only 16mm drywall. - Stuart -

Example inside out: 100mm Stud and Rockwool 12mm Board 50mm Air 12mm Board 100mm Stud and Rockwool

I can't comment on the STC question, but from what you describe what you have is A DOUBLE INSIDE OUT WALL. In reality, if you are building this INSIDE OUT wall in front of an existing standard partition wall, you will end up with a TRIPLE LEAF assembly. Not good. However, if you are building both walls, and do NOT want a DOUBLE INSIDE OUT, here is the correct way. If indeed you are building this wall adjacent to an existing 2 leaf partition wall, and you don't want a DOUBLE INSIDE OUT WALL, you need to remove the inside Leaf from the existing partition. My NON expert .02 fitZ

Hey guys, just thinking outloud. Since the purpose of the "standard" Inside out wall is to provide a "decoupled leaf", as well as framing for enclosing absorption material and fastening fabric, it occurred to me that perhaps, IF an existing standard partition wall was being incorporated as part of this assembly, it would be far easier to simply add additional layers of drywall to the existing partition than trying to lift a precision fit inside out wall with a layer of drywall, as it would seem you have to fasten the drywall on the "cavity" side of the framing prior to positioning. Even though it would not be a decoupled leaf, if additional layers were added to the existing wall, I'm wondering..if the difference in STC between a decoupled leaf, and the added layers be close enough to justify NOT building the inside out wall with drywall added? Just curious. Here is one with just the insideout wall with no drywall. Here it is with an additional layer on the existing wall. Of course, you could even make it three layers, or an additional layer on the external leaf as well. Does this make sense? It just seems incredibly difficult to build an InsideOut wall on the floor(in order to drywall it), and THEN, try to caulk everything in the cavity. GAK!! Never done it, but I thought about this many times. What's your take on this?

agreed in some cases beefing up the existing wall mass (perhaps adding a constrained layer dampening agent like GG) is a good choice. we could call the inside-out wall without drywall (or other isolation barrier) a "treatment wall" as it only provides a frame for room treatments like porous absorbers, slats, membrane panels etc. :wink: many times we even put the treatment walls on angles for some additional broadband performance...

Hi Glenn, I am living in Ireland just updated my profile. I was using the forum search to lookup details on the inside out technique but could not find any results on how inside out compares in STC to the usual setup. To make it easier for forum users to find answer I created a new thread and in hopes someone would throw a link at me with an answer. *wink*: Avare :) FitZ: Thanks for the great illustration! You are right with the complexity building a inside out construction I really like to know if the STC is around the same before going down that route. It would have great advantages to the inside treatment. Just some acoustic transparent fabric happy days! Would make wiring a piece of cake. Sorry about my bad drawing. To illustrate my situation. I have 230mm Concrete walls on 3 sides my current idea is: 230mm Concrete (existing) 50mm Air Foil 32mm Gypsum 100mm Woodstuds and Rockwool Fabric CR 1 side need to be partitioned I was thinking of: 32mm Gypsum Foil 100mm Woodstuds and Rockwool 50mm Air Foil 32mm Gypsum 100mm Woodstuds and Rockwool Fabric CR I have a feeling that there should be at least a thin rockwool slab between outside wall and the gypsum but would that improve anything? Would a foil preventing rockwoolparticles simmering into the room on the inside wall be recommended? Stuart: I see you build your studio in an similar hostile environment next to road and build inside out. How did well did your wall isolation work for you and would you do it again? OT:How well does it work to mix in a small sized CR? Helge

I was using the forum search to lookup details on the inside out technique but could not find any results on how inside out compares in STC to the usual setup.

It's the same, all other factors being equal. In other words, if the amount of mass in each leaf and the size of the air gap between the leaves is the same, then the STC will be the same. The only thing that changes with inside-out, is which side of the mass you have your studs on.

I have a feeling that there should be at least a thin rockwool slab between outside wall and the gypsum but would that improve anything?

Absolutely! You still have to put insulation in the air gap, no matter which way you build! That is part of the "spring". Fitz didn't show it in his drawings, but you still MUST have the insualtion in there (either rockwool or fiberglass).

I see you build your studio in an similar hostile environment next to road and build inside out. How did well did your wall isolation work for you and would you do it again?

My build is on hold right now, for a couple of reasons, but mainly for the SOF ("Significant Other Factor"). I have an agreement with my wife: I get to build the studio the way I want, but only AFTER I finish building the new bathroom... The bathroom is coming on (did some wiring yesterday), but still not finished, so the studio is taking a back seat right no... :(

OT:How well does it work to mix in a small sized CR?

I've not done it in my own (which will be perfect, of course! :)) but I have mixed in small studios before. It can be good or it can be hell, depending 123% on the acoustics, and 114% on the speakers :) OK, so the numbers are just for amusement, but in all seriousness in my experience those two factors are what make or break a studio. I've been in one about the size and shape of what mine will be, and it was decent. I've also been in significantly larger, supposedly "designed by professionals" studios that sounded like garbage, and left me very frustrated. That's one reason why I'm taking so much care with the design for mine: I've seen both sides of the coin, and attention to detail is what makes the difference. I'm just wondering what is the purpose of your "foil membranes"? Is that some kind of vapor barrier or other moisture control measure? - Stuart -

My build is on hold right now, for a couple of reasons, but mainly for the SOF ("Significant Other Factor"). I have an agreement with my wife: I get to build the studio the way I want, but only AFTER I finish building the new bathroom... The bathroom is coming on (did some wiring yesterday), but still not finished, so the studio is taking a back seat right no... :(

OMG! Stuart, I'm in the EXACT same situation. Bathroom half finished. Studio half finished. Only problem is..now she's looking at all those "kitchen remodel" projects on TV. :twisted: :evil: :roll: :x Add to it she knows I have a full blown woodworking shop, I'm a journeyman millworker/detailer(fancy name for cabinetmaker) and already have all the materials for the kitchen. ARRRGGGGGGGGRRRRRRR..... I told her if I don't get my studio finished soon... I might as well sell everything I've collected for over 20 years..which is how long it's taken to get this freaking far. :twisted: But when I told her I'd use the funds to buy ME a motor home....well, I think she got the picture. :mrgreen:

Fitz didn't show it in his drawings,

DOH! :shock: What a maroon. I did that for clarity but forgot to call it out in the drawing. sheeeezus it sucks getting old. :mrgreen: Also, I show regular batt insulation in both the inside out wall and the partition wall too. I meant to change the color of the insulation in the inside out wall to show it was 703 and call it out too...gak!...alzhiemers strikes again. :oops:

Soundman2020 wrote:

My build is on hold right now, for a couple of reasons, but mainly for the SOF ("Significant Other Factor"). I have an agreement with my wife: I get to build the studio the way I want, but only AFTER I finish building the new bathroom... The bathroom is coming on (did some wiring yesterday), but still not finished, so the studio is taking a back seat right no... :(

Sorry to hear I know the feeling loosing momentum during such a process is the worst. I am somewhat lucky that my wife wants me out of a room in our little cottage and into the shed. In order to get there its in her interest thats my project is getting done :=) I just need to make sure I get everything incl. inside treatment done before she finds a way to get me out of the cottage :twisted: :twisted:

Soundman2020 wrote:

I'm just wondering what is the purpose of your "foil membranes"? Is that some kind of vapor barrier or other moisture control measure? - Stuart -

It is. There is plenty of rain here in ireland and there might be some moisture stored in the outside wall that need to vent somewhere. Thats where an air-gap between outer wall and stud wall would come in handy. I just dont know yet where to put it. Helge

Stuart, I'm in the EXACT same situation. Bathroom half finished. Studio half finished. Only problem is..now she's looking at all those "kitchen remodel" projects on TV.

I hear you, but that ain't gonna happen here! You have to draw the line somewhere... Besides, My wife is on-board with the whole studio thing, so it won't be an issue. However, AFTER the studio is built, it remains to see how much time I'll be allowed to spend in it, rather than on those "other" projects! :)

I did that for clarity but forgot to call it out in the drawing.

Yeah, I figured it was for clarity. It would look pretty complicated and muddled if you showed it in there. It's much clearer without it: Makes it obvious where the air gap is. - Stuart -

the STC per Stuart will depend on the mass and air gap components. now that studiotips.com is back online, you can download Eric Desart's incredible MSM spreadsheet which can give you a rough estimate on the isolation you could expect. that said, if you do things correctly the isolation is quite high as you would expect from "normal" construction with the benefit of exposing a huge absorptive surface ready for slats and etc.

You guys are brilliant I love how passion everyone is about studio design in this forum.

gullfo wrote:

the STC per Stuart will depend on the mass and air gap components. now that studiotips.com is back online, you can download Eric Desart's incredible MSM spreadsheet which can give you a rough estimate on the isolation you could expect. that said, if you do things correctly the isolation is quite high as you would expect from "normal" construction with the benefit of exposing a huge absorptive surface ready for slats and etc.

Here a direct link to the MSM spreadsheet: http://forum.studiotips.com/viewtopic.php?t=1414 One has to become member at studiotips.com to be able to download those files. However it does not seem to work under my Mac with openoffice (neooffice). Wont bother to install an MS office in my vmware for that. To make an uneducated guess I would say both walls should be behyond 60dB STC. Looking at ir693 (page23) they have a double leave wall with 2x12.5mm gypsum 89mm Wood and Rockwool 25mm Air 89mm Wood and Rockwool 2x12.5mm gypsum Listed with an STC of 66 so if it stays the same with inside out install I would be having 66. I guess the wall in front of the concrete is including concrete wall beyond 66. Besides I will be having 50mm air. Greetings Helge

Hi, got a new view on this subject by user space on the recording.org forum http://recording.org/showthread.php?p=365939 quoting space: ----------snip------------- Directly to the inside out wall, it is only as good as the counter-part typical double framed assembly. That means that the air space has to exist in the same form from one to the other or it is a different assembly, with different stc or TL ratings. An assembly that is framed the exact same way, with the same decoupled air space, with a hard boundary on the exterior but has the hard boundary on the interior of the inside framing will have an air space of approx. 8 inches. This difference of 8 inches versus 4 1/2 inches is where the low frequency suffers. In order to get the same transmission loss using an inside out assembly, the interior framing would have to be re-set to have a distance of 4 inches between frames to match the same type assembly that is typical room-in-a-room. --------snap------------- He gave me as well a headwash on the therm STC: http://en.wikipedia.org/wiki/Sound_transmission_class "The STC number is derived from sound attenuation values tested at sixteen standard frequencies from 125 Hz to 4000 Hz. These transmission-loss values are then plotted on a sound pressure level graph and the resulting curve is compared to a standard reference contour." To illustrate this see picture: As "reference" I took ir693 from the NRC page 23: http://www.nrc-cnrc.gc.ca/obj/irc/doc/p ... /ir693.pdf As the STC value of that document the only measurement result I have at hand. PICTURE: Example 4 is as version (c) in ir693 page 23 25mm Gypsum 89mm Woodstuds and glasfiber batt 25mm air 89mm Woodstuds and glasfiber batt 25mm Gypsum resulting in leave to leave distance of 203mm with an STC of 66 structure 1-3 is with a solid wall (grey) question was is structure 2 the same as 5 a triple leave system? Greets Helge

#2 and #5 are both 3-leaf- The rest are 2-leaf, but with different levels of isolation. I', guessing that #5 would be the worst isolator, and either #1 or #4 would be the best. Your "other forum" guy seems to be saying the same as we have been trying to tell you, just in different words. There is no difference at all in the amount of isolation you get from a "normal" wall or an "inside-out" wall, if the masses and the air gap are the same. The equations do not even consider which side of the mass you have the studs on: it simply is not a factor. - Stuart -

myterion, I haven't been posting over here much lately... but what Brien and I been on about, over at RO... yes, 2 & 5 are triple leaf, with the rest being 2 leaf. In your initial scan, the top illustration is indeed a 3 leaf, and the bottom is a 2 leaf. Stuart is absolutely correct in pointing out the air column detail. (That was part of my illustration of the 2-2x4 stud walls being 33" apart in Jim R's thread.) As to Eric's spreadsheet... If you can find it, look for a copy of a MS Spreadsheet reader application. It was someone's open source thesis, I believe. I found it in some out of the way university archives. It lets you open and interact with all older versions of spreadsheets... and you can print them... you just can't save or add new calculations. Eric might even have a link to it in his archive. The easiest way to think about MAM is to simply count the places where there is a volume of air and add 1. That will tell you how many leafs.

Soundman2020 wrote:

Your "other forum" guy seems to be saying the same as we have been trying to tell you, just in different words. There is no difference at all in the amount of isolation you get from a "normal" wall or an "inside-out" wall, if the masses and the air gap are the same. The equations do not even consider which side of the mass you have the studs on: it simply is not a factor. - Stuart -

Hi Stuart I suppose there was a bit of wishful thinking going on in my head.

myteron wrote:

Soundman2020 wrote:

Your "other forum" guy seems to be saying the same as we have been trying to tell you, just in different words. There is no difference at all in the amount of isolation you get from a "normal" wall or an "inside-out" wall, if the masses and the air gap are the same. The equations do not even consider which side of the mass you have the studs on: it simply is not a factor. - Stuart -

Hi Stuart I suppose there was a bit of wishful thinking going on in my head.

Myteron...the other forum guy "Space"...that is me.... Sorry for the confusion.

we had to force him to use xspace because "space" is something between the isolation mass and didn't want to confuse people :)

Well, "X" is a prime number in this business Glenn :)

I thought we had established that space is besides mass the most important part :P

I thought we had established that space is besides mass the most important part

Yup! That's why you need so much of it! And "X" sure is a lot, since it is an unknown quantity in mathematics! (But in acoustics it seems to be a PRIME unknown quantity!) :)