I was just thinking of a possible way to get more out of an existing 2x4 wall. Say you open one side to put in insulation. While you're in there, what if you took a saw to the inside of the studs, creating a 1/8" gap? You'd end up with a double-stud wall with 2x2 studs. Anybody looked into that before? I assume you couldn't do this to a load-bearing wall, but what about non load-bearing?

I can't imagine what kind of saw you would need to pull off this trick. Most people have a lot of nails that would be in the way. I think a better solution is to open up one side of the walls then lay down a 2x2 next to the bottom and top plates and insert staggered studs. You could even cut the 2x2 down to an inch even so net you are investing 2 inches wall to wall to convert a room to staggered stud.

Even if this were structurally safe, it would not give you the sound isolation benefits of double studs. For one thing, you are sharing common plates, as in staggered stud construction. And you are not increasing the air depth between the leaves of sheetrock, which is an important component of both staggered and double stud construction.

If you've got the sheetrock off the wall, a much better solution is to lay down a second base and top plate, and make a true double stud wall.

Regards,
Terry

Someone over at cocoontech.com suggested adding a 2 x 2 stud wall, abutting an existing 2 x 4 wall.

Last weekend I doubled the depth of one of my mechanical room walls - cheap and easy project. Not to de-couple, but to increase the depth of the wall for wire management, and to continue the normal use of the bathroom wall on the other side, for hanging pics (trying to increase WAF of multiple recessed enclosures in the mechanical room).

Also, the increased depth will allow more flexibility for adding an electronically controlled valve to the water main pipe, inside the wall. The water main valve will be tied to the alarm system's water sensors, to avoid floods.

Someone over at cocoontech.com suggested adding a 2 x 2 stud wall, abutting an existing 2 x 4 wall.

Last weekend I doubled the depth of one of my mechanical room walls - cheap and easy project. Not to de-couple, but to increase the depth of the wall for wire management, and to continue the normal use of the bathroom wall on the other side, for hanging pics (trying to increase WAF of multiple recessed enclosures in the mechanical room).

Also, the increased depth will allow more flexibility for adding an electronically controlled valve to the water main pipe, inside the wall. The water main valve will be tied to the alarm system's water sensors, to avoid floods.

http://www.soundproofingcompany.com/upload/SPC-Staggered-Stud-Wall-Guide.pdf

You would not want the 2x2 wall next to the 2x4 wall if the 2x4 wall still has drywall. remove the drywall, then build the 2x2 wall or modify the existing 2x4 wall as described in the attached link.