Originally Posted by gullfo
Couple of things to consider, if you have 2 back to back 2x4 walls with a 2 inch gap, you have 9 inches of air space. Filling that with R13 on each side will leave a small open air space which will allow the pressure in that space to flow and equalize. This "loose" air space will help much more than dense insulation or a lot of sealed air pockets. If you have the space, use more, if not, recognize that the framing has space "built in" so the actual gap between the frames can be as little as 1 inch and still have plenty of air space. As noted make sure the room air space is sealed from the inter-wall air space for best performance.
Great reply gullfo, you've actually made me realise the space in the studs too. even though I somehow knew that before too, now its even more clear.
I'm going to build my walls around the the house columns which are 14 inches, so I was thinking for metal studs 4 inches.
Put one on each side of the column with gap between the studs 4.5 inches (including the space I need for drywall)
Then fill the studs with insulation 4 inches each as well (40kg/m3 rockwool). So I will have 8 inches of insulated air (both sides) and 4.5 inches pure air.
Do you think is there anything I could do better? I mean maybe if put less rockwool would better as an example? anything? Or is it good enough?
Was wondering about my columns, they are solid concrete 14 inches, would they be good enough on their own without soundproofing?