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Discussion Starter #1 (Edited)
Decoupling theory - is hat channel necessary if wall never touches joist

So I'm a bit crunched for horizontal space on my foundation walls and I'm curious if I would need clips and hat channels for those walls...

What makes this unique is that I don't have a top plate nor a bottom plate. I'm adhering rigid foam insulation to the foundation wall then I'm attaching 1x3 furring strips do the foundation wall through the insulation

My question is, if my 1x3 "studs" and double drywall/GG never touch the joists or the floor then would clips and channels make that big a difference?

It seems like the sound would hit the drywall, move to the joists, hit the foundation wall (which would have incredible mass) then move through the foundation to the to the joist.

Thanks,
Joe
 

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So I'm a bit crunched for horizontal space on my foundation walls and I'm curious if I would need clips and hat channels for those walls...

What makes this unique is that I don't have a top plate nor a bottom plate. I'm adhering rigid foam insulation to the foundation wall then I'm attaching 1x3 furring strips do the foundation wall through the insulation

My question is, if my 1x3 "studs" and double drywall/GG never touch the joists or the floor then would clips and channels make that big a difference?

It seems like the sound would hit the drywall, move to the joists, hit the foundation wall (which would have incredible mass) then move through the foundation to the to the joist.

Thanks,
Joe
If the 1" x 3" furring strips are anchored to the foundation, and the double drywall is anchored to the furring strips, then you've coupled the wall directly to the foundation. Am I interpreting the drawing & description correctly?

That would defeat some of the isolation, particularly low frequency. It avoids transmitting energy to the floor joists above, but the design provides significantly more contact between wall and the foundation allowing energy to be transmitted to the foundation versus being absorbed by a decoupled DDW/GG wall which is free to vibrate/oscillate.

Seems like you could frame up a wall with a bit of separation between the studs and the rigid foam. Build the wall shorter than the ceiling. Use IB3 clips to isolate the wall from the ceiling joists. Then attach the DDW to that now isolated wall. Typical room-in-room techniques. Only the bottom plate would be in contact the floor/foundation.

Perhaps you could turn the 2"x4"s 90 degrees to make the framed wall 1 1/2" thick instead of 3 1/2" thick. If that is workable with building code, you might only lose 1" from the design above.
 

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Discussion Starter #3
If the 1" x 3" furring strips are anchored to the foundation, and the double drywall is anchored to the furring strips, then you've coupled the wall directly to the foundation. Am I interpreting the drawing & description correctly?
yes, it would be anchored to the furring which are anchored to the foundation. I figure with the incredible mass of the foundation it would absorb most of the sound before ever hitting the joist.

That would defeat some of the isolation, particularly low frequency. It avoids transmitting energy to the floor joists above, but the design provides significantly more contact between wall and the foundation allowing energy to be transmitted to the foundation versus being absorbed by a decoupled DDW/GG wall which is free to vibrate/oscillate.

Seems like you could frame up a wall with a bit of separation between the studs and the rigid foam. Build the wall shorter than the ceiling. Use IB3 clips to isolate the wall from the ceiling joists. Then attach the DDW to that now isolated wall. Typical room-in-room techniques. Only the bottom plate would be in contact the floor/foundation.

Perhaps you could turn the 2"x4"s 90 degrees to make the framed wall 1 1/2" thick instead of 3 1/2" thick. If that is workable with building code, you might only lose 1" from the design above.
The other option would be to install a RC instead of clips and hats for the foundation walls. It would certainly be better than nothing and would save me an 1.5" and money. I know RC's are frowned upon but if carefully installed they still function? For the ceiling and interior walls, I'd use clips and channels.

Thoughts?
 

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yes, it would be anchored to the furring which are anchored to the foundation. I figure with the incredible mass of the foundation it would absorb most of the sound before ever hitting the joist.
Because the concrete is rigid, there is minuscule movement to absorb sound energy. The foundation wall will transmit sound to other parts of the house. The ability of the heavy DDW to vibrate helps it to absorb sound wave energy.

Read through this post and this post from Dennis Erskine. Also have a read through the first few posts of this thread.

There may be other views in the acoustic thread/sticky

The other option would be to install a RC instead of clips and hats for the foundation walls. It would certainly be better than nothing and would save me an 1.5" and money. I know RC's are frowned upon but if carefully installed they still function? For the ceiling and interior walls, I'd use clips and channels.

Thoughts?
If you frame a decoupled wall (ie, not touching the joists above) ideally 1" (no less than 1/8") from the rigid foam, then you don't need clips and channels or RC before installing the DDW/GG.
 
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