Full room-within-a-room construction advisable in basement?

D

drhfk

New member
We are building a band rehearsal space in our single-family home basement. All four walls are made of concrete-filled cinderblock. Two of the walls are foundation walls that back directly into the soil (the house is on a slope). Like this:

Code: 
		Soil
		####(1)####
Soil	        #         |
	       (2)       (4)
		#         |
		#---(3)---+

We're trying to decide between building:

(A) a four-wall "room within a room" inside the existing walls (1)-(4); or
(B) a room that's using walls (1) and (2) "as is" and only build floating/decoupled walls facing the existing walls (3) and (4).

In each scenario, we would build a floating floor and ceiling. Given the location and the nature of the outside walls, is scenario (A) overkill? Any suggestions would be greatly appreciated!

drhfk
 
Are you trying to 'soundproof' the room, in other words keep outside sounds out and inside sounds in? If so, sound can be transmitted through the concrete walls, although not as much as wood walls.
 
I've been trying to educate myself on this subject lately, and from what I understand, you're right mjb. Even concrete walls that are against earth will transmit vibrations to the structure of the house. Even though earth is a pretty darn good damping material, it doesn't stop the foundation from resonating/vibrating and passing those vibrations along to anything that touches it.
 
yeah, I knew a guy who took old tires and chopped out chunks to put between walls/floors/ceiling etc. Seemed like a pain in the ass to me but apparently it worked.
 
It depends how much isolation you're shooting for.

The walls backed by soil will, in themselves, be okay. Your problem will be where they meet the ceiling and/or extend up to the next floor. I can't think of any way to get ideal isolation without the full "box in a box".

I'm sure you've already considered it but you lose a lot of floor area and headroom doing this sort of thing though.
 
I agree.

You MAY not need it. Please post a drawing with dimensions... also photos showing the space and how it is built. Basements are usually built on the soil, without a space underneath, therefore this type of structure would be termed 'infinitely stiff', not transmitting nor causing resonances. A sand-fill here or on any slab-on-grade is unnecessary and will do little or nothing for sound-proofing or even acoustics within the space.

Your concern should be on any windows and/or walls that sit above the ground. These and the ceiling/floor above are the major issues. Also note that you will NOT need to float the walls in this situation. -- While you may need to build separate, isolated walls for STL, you don't need to sit them on rubber or anything like that. Connect them directly to the basement concrete floor.

You may be able to weave new ceiling joists in between the existing floor joists above to create your isolated ceiling. These isolated ceiling joists will sit on the new iso walls... nothing touches the structure except a few resilient sway braces to keep everything straight. If you can't do the iso ceiling joists, you'll need to check into resilient hangers. Please note that I have started with the 'best' isolation technique first. Hangers vary from very good to barely adequate. Look up the specs and testing data, as well as the load range. -Warning, this can get expensive. ;)

Cheers,
John
 
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