# Triple Leaf Solutions?



## sandbag (Aug 2, 2009)

Please share your thoughts on this issue:

I've stripped down the walls and ceiling of my proposed home theater room to increase dead air space between the double walls of a room within a room rebuild in your classic double drywall Green Glue assembly. This will yield about 8.5" of dead air space (3.5" wood stud + 2" space + 3.0" steel stud) between leaves. The finished room dimensions will be about 15' x16' x 8.5' height. The room is now 16' x 17' x 9.'

The problem is: two of the walls had shear panels on the theater side of the existing wall. I'll be able to move the shear panels to the other side of one of the walls (the front wall of the theater ), and half of the other wall (a side wall). However, the rear half of that wall adjoins a guest bedroom. My spouse forbids messing with the bedroom, so I cannot move the shear panels to the bedroom side, nor can I add a second layer of drywall to the bedroom wall. So, I am forced to nail 1/2" structural plywood to the theater side stud face along that 8 feet of wall. 

This part of the wall will thus have the dreaded triple leaves. Due to a doorway on the rear wall I cannot space the new wall more than 2.0" from the shear wall, leaving a maximum of 5.0" of dead air space. 

Possibilities before reinstalling the shear panels:

1. Running a bead of drywall adhesive along the bedroom drywall/stud joints to reduce panel vibration on the drywall nails.


2. Adding mass to the bedroom side leaf by inserting 14.25" wide pieces of drywall w/ GG between the studs (I'm already doing this between the joists on the underside of the floor decking), but there is much more wood in the shear wall (doubled studs, blocking and fire stops). 


3. Filling the stud spaces level with the stud faces, by adding several more layers of drywall, then surfacing with wire mesh & stucco, then "buttering" with GG before renailing the shear panels.

4. Adding 5/8 drywall over the renailed shear panel with gg, but thereby decreasing the dead air space between the walls by another 5/8" down to 4.25" 

What do you recommend, besides the obvious non-option, wrecking the bedroom? Any tricks? 

How bad is bad in this arrangement? Would venting the between wall dead air space to an entry vestibule have any benefit on reducing the sound transmitted to the bedroom, by avoiding the trapped air being a mass-spring resonator?


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## bpape (Sep 14, 2006)

I'd suggest #2 - and let the noise ring through to the bedroom - maybe that'll get her to change her mind 

Bryan


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## sandbag (Aug 2, 2009)

Thanks - Are there tips on this site for uploading drawings and photos? Normally its a breeze with my Mac, but not here.


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## bpape (Sep 14, 2006)

Upper right corner of the screen are a row of buttons. Find the one that's marked GALLERY. Hit that. Then you can use the upload link to upload the pics and reference those in your posts.

Bryan


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## sandbag (Aug 2, 2009)

Duh - thanks!
Back to original question - I can cut a couple of 3" circular ventilation holes in the shear panel for each stud space without compromising structure. Might that avoid the ringing spring mass resonator effect, do you think?


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## bpape (Sep 14, 2006)

Will it help a little? Maybe. 

The other option, though a bit extreme, would be to completly fill the stud cavity with layers of MDF to make the entire wall 1 very thick, very dense 'leaf'

Bryan


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## sandbag (Aug 2, 2009)

My wife is happy. I assume GG between the drywall and MDF, anything between successive MDF layers or just screw them tightly (w/ MDF I'll have to predrill, so tight shouldn't be a problem)?


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## bpape (Sep 14, 2006)

You'll want to attach them somehow so they don't rattle any. You don't have to use Green Glue between each layer, maybe just between the outer layer on each side. Use something like a dab of liquid nails here and there in addition to the screws for the other layers.

Bryan


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## sandbag (Aug 2, 2009)

What about substituting cheaper particle board, sound board or rigid foam for a couple of the layers? I assume you like the internal damping characteristics of MDF, but in a 3.5" chunk, thats a lot of MDF. I'm also thinking that's a lot of shear resistance in the wall. Maybe enough to forget the panel?


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## bpape (Sep 14, 2006)

I don't know if they'll allow you to skip the outer panel. Kinda doubt it as that's the one that ties the studs together. The inner ones won't.

You can use particle board certainly. Could even use drywall or plywood - whatever's cheaper. Foam isn't going to work well as it is still going to act like an airspace.

Bryan


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## Ted White (May 4, 2009)

You could have removed the plywood sheer wall and replaced with metal straps to accomplish the same shear value.


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## bpape (Sep 14, 2006)

I wondered about that but wasn't sure about his local code specifically. Sometimes, they get pretty specific.

Bryan


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## sandbag (Aug 2, 2009)

Yeah - we got new codes after the Northridge, California quake. Surprisingly, I can't find a structural engineer that will stake his professional standing on other than a like kind retrofit. They've calculated shear based on 8d nails spaced 6" apart on the perimeter of each 4x8 panel - total of 60 nails minimum. If there's an opening then its blocked with 4x4 between the studs and then banded with metal strapping. I'm originally from Michigan, so this is new to me too. I don't mind the extra labor & materials to fill the studs if that'll make for better bass attenuation. The critical factor is the minimal airspace between opposing leaf surfaces - just 4." I can't find any data to suggest what I'll lose by halving the air space.


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## Ted White (May 4, 2009)

If you proceed with the second framed wall in front of the shear wall and fill the cavity of the original shear wall, you'll be affecting the resonance point of the completred double wall assembly. Smaller air cavity will increase the resonance point, resulting in reduced low frequency performance. Adding a lot of mass to that original wall (assuming we maintain a single air cavity) will lower the resonance point.

So smaller air cavity and more mass work in opposite directions. What will the result be? Hard to say. 

Additional info on shear walls: http://www.toolbase.org/PDF/DesignGuides/ShearWallDesignGuide.pdf


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## sandbag (Aug 2, 2009)

Interesting. Steel x-bracing. I have wooden studs, not steel. Would the strap require some special damping between studs? 

I won't have the top plate issue because it sits under a double 2x12. So- if I add end stud buckling protection, I might be okay.


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