Keith!! thanks for the nudging.
Been busy . . .
Actually I was out hanging drywall on 13' ceilings when I saw the message come through. I have been spending most of the summer finishing the addition to my building getting it ready for insulation and heat as the colder Pennsylvania weather will soon be upon me.
All my ductwork is finished (insulated), the control room is framed in, so soon I will be starting on the studio framing.
One issue I still have is the "outer" leaf. On the old part of the building (lower ceiling I filled in between the studs with two layers of dry wall (pain in the ass), as the exterior was a fiber board with vinyl siding. On the addition (high ceiling) I sheathed the exterior with 7/16" OSB and then the James Hardie board which is a cement based 4'X8' sheathing. My big question is how much difference would I expect in sound transmission loss if I just put drywall on the interior of that wall as opposed to in between the studs as I did on the old part. I realize that I am breaking the two leaf rule. However, what typically does one do with a new building such as this.
Here are a few photos.
Mark
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edenorchestra
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Mark
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sharward
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Welcome back, Mark!! Long time no see! It's great to see that there's been so much progress on your project!
Even I just discovered that I'm going to have a third leaf on one of my walls.
In your case, it appears you are proposing to make a third leaf because "beefing up" the outer leaf would be difficult, based on your existing construction area beef-up effort.
I think this is the first time I've seen a new construction third leaf proposal.
The reason that I don't see that a lot is because it's generally a bad idea.
Assuming you haven't finished the outer surface of the wall, I think you'd be better off applying more mass to the outside. This avoids the "strips between studs" situation. What are you planning to use as your final layer? If stucco, you may not have to do more than that, especially if it's a liberal application (i.e., maybe an inch).
However, I can't see how strips of drywall between the studs on the inside would be that difficult. You have OSB as your first outer layer, which means you have a nice, flat surface to screw the drywall strips into. What's so bad about that?
Fact is, you have to add a lot of mass to make up for the detriment of a third leaf. I don't have the fancy calculators to tell me how much, but it's fair to say that placement of mass matters -- you can't move mass from a two layer system to make a third leaf and not expect to take a significant hit in your isolation.
--Keith
Sometimes third-leaf situations can't be avoided. Well, I suppose technically they could always be avoided if cost and effort were never an issue. Typically, those scenarios occur in existing instruction.edenorchestra wrote:. . . On the addition (high ceiling) I sheathed the exterior with 7/16" OSB and then the James Hardie board which is a cement based 4'X8' sheathing. My big question is how much difference would I expect in sound transmission loss if I just put drywall on the interior of that wall as opposed to in between the studs as I did on the old part. I realize that I am breaking the two leaf rule. However, what typically does one do with a new building such as this.
Even I just discovered that I'm going to have a third leaf on one of my walls.
In your case, it appears you are proposing to make a third leaf because "beefing up" the outer leaf would be difficult, based on your existing construction area beef-up effort.
I think this is the first time I've seen a new construction third leaf proposal.
The reason that I don't see that a lot is because it's generally a bad idea.Assuming you haven't finished the outer surface of the wall, I think you'd be better off applying more mass to the outside. This avoids the "strips between studs" situation. What are you planning to use as your final layer? If stucco, you may not have to do more than that, especially if it's a liberal application (i.e., maybe an inch).
However, I can't see how strips of drywall between the studs on the inside would be that difficult. You have OSB as your first outer layer, which means you have a nice, flat surface to screw the drywall strips into. What's so bad about that?
Fact is, you have to add a lot of mass to make up for the detriment of a third leaf. I don't have the fancy calculators to tell me how much, but it's fair to say that placement of mass matters -- you can't move mass from a two layer system to make a third leaf and not expect to take a significant hit in your isolation.
--Keith
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edenorchestra
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Hey Keith . . well the outside is DONE . . so I will beef the inside with drywall. You are correct that it is not that hard, my studs are pretty true. The Hardie board http://www.jameshardie.com/ has an exterior pattern like T-111 and comes primed. It is all painted and trimmed out . . so I am leaving that alone. I just have to snip the few extra nails on the inside that I mis-fired when I put up the sheathing. Today we are going to finish the second ceiling layer of the first leaf . . glad that will be over with . . I am getting a sore neck from srew gun . . .
Mark
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sharward
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Aha! You were holding that photo out on us! 
On the plus side, I think that exterior surface is quite heavy and will probably count as much as stucco, which is heavier than drywall. On the other hand, OSB is lighter. So, I think you basicaly have two layers on the outside right now (one great, one not-so-great). Add two or three layers of drywall strips between studs and I would think you'd be golden!
--Keith
On the plus side, I think that exterior surface is quite heavy and will probably count as much as stucco, which is heavier than drywall. On the other hand, OSB is lighter. So, I think you basicaly have two layers on the outside right now (one great, one not-so-great). Add two or three layers of drywall strips between studs and I would think you'd be golden!
--Keith