Exterior block wall options

[ScotcH]

Starting construction soon ... one last decision to make.

Given everything else being equal, which of these 2 wall designs would be the better option? Is the 1" air (pink stuff) just basically a waste of space, and would the single leaf design be similar, or even better? What about the concrete block wall itself ... does it already act as a 2 leaf because it's hollow blocks, or does the mass of the blocks, and the fact that the air gap is not contiguous negate that?

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[gullfo]

the left hand one is fine for isolation up to a point - the earth damping on the majority of the wall helps. make sure to address moisture and moisture barriers.
of course the rest of the space - ceiling, windows, doors, structural transmission etc will all limit the actual level of isolation - most residential structures even with the iso goodies will probably only ever be 50db or so of true LF isolation because the structure transmission begins to take over. sympathetic vibrations can also creep in as highly audible at that point...

[ScotcH]

Thanks Glen. I definitely feel that the exterior wall will not be the weak point in my basement build (ceiling very likely), so I think I'll simplify and go with the left option.

Moisture and thermal break is provided by the rigid foam, it is sealed with spray foam at the header, and sealed all around with caulk. Pretty typical for basement build in Ontario. The not-typical part is having the studs on the outside of the drywall, lol.

[Paulus87]

Thanks Glen. I definitely feel that the exterior wall will not be the weak point in my basement build (ceiling very likely), so I think I'll simplify and go with the left option.

Moisture and thermal break is provided by the rigid foam, it is sealed with spray foam at the header, and sealed all around with caulk. Pretty typical for basement build in Ontario. The not-typical part is having the studs on the outside of the drywall, lol.

If going with a one leaf system using concrete blocks then the second layer of drywall is unnecessary, in fact, both layers of drywall are not needed at all in terms of sound reduction, but I imagine you want to have at least one layer in order to dry line the basement space?

The reason it's not needed is that your concrete blocks are already incredibly dense, you would need to double their mass in order to gain about 6db of transmission loss, so the drywall mass pales into insignificance as far as adding any valuable isolation to the mix.

If you were to build a fully decoupled double leaf assembly with a significant air gap then that would be a different story.

Paul