Framing exterior wall against concrete foundation

[christophercarr86]

I am building my studio in the corner of a basement as a room within a room. So currently the space I will be using has 2 exterior walls that are poured concrete foundation and 2 interior load bearing walls to the other part of the basement that are 2x6.

My question is regarding the exterior walls.
Do I need to frame out an "exterior studio wall" (see the blue arrows) to tie into the load bearing walls to have a completely mineral wool insulated exterior wall ?
Or do I just build the inner room 1" from the foundation walls and load bearing walls ? and consider my outer walls already done ?

My worry was that sound would escape the inner wall along the foundation and to the upper floor above because it would only have 1 wall worth of mineral wool against the foundation ? Its only framing 2 more walls so not a huge deal and want to do it if it will give me some benefit, but if I can save that space in the room I would like to.

I attached a drawing to help better show what I mean.
The 2 exterior walls are (grey walls are the poured concrete foundation) and 2 interior walls (red ones are existing load bearing 2x6 walls). The blue arrows are showing the part I am questioning the need to build ?

[gullfo]

the additional framing would be useful to increase the air gap depth and act as a retainer for more insulation. that said - if the wall frames are attached to the house framing (walls, joists, foundation etc) then there will be structural transfer. most times where you are adding exterior mass layer walls, these are connected to the house frame, and the interior mass later walls are decoupled (isolation bracing, underlayment isolators, etc) to reduce the direct transfer into the foundation and walls from those interior surfaces.

generally speaking, residential construction even with proper care and effort can realistically only achieve about 50db transmission loss due to structural transfer becoming the predominate source in exterior spaces. now this may be something akin to a low volume radio faintly heard, but its still there. so if your interior sound levels are 110db, you still have potential (especially LF energy) of 60db (which is fairly quiet, and if you are listening in your CR (for example) you likely wouldn't notice as the monitoring level is higher.

[christophercarr86]

From my understanding, the "exterior wall" will be the 2 load bearing walls of the house and the 2 foundation walls, as they are all tied in together with the joist system for the floor above. The mass of 2 walls of my outer walls in the concrete foundation which is better than any type of mineral wool inside some framing.

Then my interior wall would be 4 fully framed walls 1" inside the 2 load bearing walls and 2 foundation walls.

I just wanted to make sure those 2 foundation walls were ok with no "exterior" layer of mineral wool and that the concrete was taking the place of that in those 2 walls.

[gullfo]

that approach of using the existing concrete walls should be ok - ensure proper moisture/vapour barrier protection as insulation will/should likely press against those walls.

[christophercarr86]

I am new to the forum and just realized that I didn't have the location on my profile filled in. So likely why I didn't get many responses. Just leaving a comment to say that my profile has been updated with my location!

Sorry about that everyone! Looking forward to speaking with everyone and contributing where I can !