3 Leaf thoughts..

I've been thinking about this and I came up with this thoughts: - Lets say you have two rooms in your house (next to each other), with concrete walls, and you want to further isolate them. What to do? I would build a inner stud wall on each room. Whats the problem with that? You get 3 leafs (counting the existing concrete wall thats left in the middle) Now? Whats worse? A 3 leaf system that way, or just leave the wall alone. or even tho, beef them up? When comparing 3 leafs system, you compare it to the case where the "middle" leaf doesnt exist, and its pretty clear : The air gap in the middle would be bigger, so, better isolation. But what happens with you do compare a 3 leaf system to the original scenario? I think it will help isolation.. not as much if the middle concrete wall didnt exist.. ? Also, what would you do in such situations? Just beef up one side of the concrete wall, and build a decoupled inner leaf on the second room? What if you built a inner leaf in room #1 DIRECTLY attached to the concrete wall? Will it act as 2 leafs even if they are completely coupled? Wouldnt it become just 1 leaf? Looking at it just by "beefing up" Any thoughts about this? - Javier

If you have a concrete wall, that's a pretty substantial amount of mass and density right there. If it is a thick concrete wall, even better! The density of concrete is about 2,500 kg/m3, which is roughly four times the density of drywall. So if you have a concrete wall that is, for example, 10cm thick, then you'd need 40cm of drywall to match the amount of isolation that you are getting from the concrete wall. You would need 27 layers of drywall to do that!!!!!

Also, what would you do in such situations? Just beef up one side of the concrete wall, and build a decoupled inner leaf on the second room?

Not worth beefing it up, for the same reason as above. Assuming that your wall is just 10cm thick, to get an increase in isolation of 6 dB (mass law), you'd have to add 27 layers of drywall as your "beef"...

What if you built a inner leaf in room #1 DIRECTLY attached to the concrete wall? Will it act as 2 leafs even if they are completely coupled? Wouldnt it become just 1 leaf?

If it is fully and directly coupled to the concrete wall, them yes, it would only act as one leaf, but if there is an air cavity in between then you might still have some resonance issues that would be difficult to predict and even harder to treat... I may be off base here, and perhaps John or Rod or Ro or Andre can chip in here with their recommendation, but to me the mathematics of it suggests that you could go with a stud wall on either side of that concrete wall, with a couple of layers of drywall on the studs, and I don't think you'd have much of a three leaf effect at all, due to the sheer mass of the concrete wall in between. If both rooms are on the same (coupled) floor, then my guess is that you'd get more flanking through the floor itself than you would from the three-leaf effect. That's my twelve pesos! (= US$ 0.02)!! :) - Stuart -

Thanks Stuart. Thats what I thought actually. Actually, these walls are 20 cm thick, and 27 cm thick to the outside world, so thats pretty good actually. One thing tho, I was triying to find a software that could calculate STC depending on your walls, like for example: What would be the final STC of a 20 cm concrete wall against a decoupled studwall with 2 layers of drywall. Anyone knows or have this kind of software? I know there is some..

jbassino wrote:

One thing tho, I was triying to find a software that could calculate STC depending on your walls, like for example: What would be the final STC of a 20 cm concrete wall against a decoupled studwall with 2 layers of drywall.

Look at NRC IR 586 and IR761 for actual test results for concrete block and gypsum board walls. IR 586 includes test data showing the effect of a third leaf on a wall. Andre

jbassino wrote:

One thing tho, I was triying to find a software that could calculate STC depending on your walls, like for example: What would be the final STC of a 20 cm concrete wall against a decoupled studwall with 2 layers of drywall.

Look at NRC IR 586 and IR761 for actual test results for concrete block and gypsum board walls. IR 586 includes test data showing the effect of a third leaf on a wall. Andre

jbassino wrote:

One thing tho, I was triying to find a software that could calculate STC depending on your walls, like for example: What would be the final STC of a 20 cm concrete wall against a decoupled studwall with 2 layers of drywall.

Look at NRC IR 586 and IR761 for actual test results for concrete block and gypsum board walls. IR 586 includes test data showing the effect of a third leaf on a wall. Andre

Thanks Andre, thats a great source of info I didnt know about I'll read it!

Yeeeehaaaa!!!! Andre´s back!!!! :yahoo: Woooohoooo!!!! :) (We missed ya!) - Stuart -