I am aware of diaphragm shear value

[Mountainrunner]

I am aware of diaphragm shear values for plywood nailed directly to rafters

I am aware of diaphragm shear values with 1x solid lumber nailed to rafters

but...

I don't know of any lateral shear values for plywood over skip sheathing

any suggestion...

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I have a project owner wants to remove flat ceiling framing to frame a vaulted one (see attached sketch)...
however....the roof plywood is not nailing directly to the rafters but...it is nailed to skip sheathing...and...I don't know if there are any lateral shear values for such conditions...

is there are not shear values for such condition...could it be that the flat ceiling works as the diaphragm?

any advice/suggestion on how to address this..if owner insist in removing the flat ceiling framing...

 

[DoubleStud]

Wouldn't it just a matter of field and edge nailing of the plywood? Following!

What is skip sheathing anyway? I haven't seen it before.

 

[Mountainrunner]

I did not know about skip sheathing myself until...I got the project/ mentioned before....and I google "skip sheathing"...

 

[driftLimiter]

If Im understanding correctly when you say skip sheathing it means that some 1x slats are positioned like purlins over the top of the joists and the plywood is above that and fastened to that.

I'm thinking that the diaphragm is the plywood, the slats are the plywood support.

NDS requires minimum width of members at panel edges to achieve different diaphragms strengths.

I don't see any reason why you dont have a normal Structural Wood Diaphragm if you have adequate sheathing thickness/grade, nail pattern and type, and sufficient size of blocking members.

Think about a normal piece of plywood its supported at 2' o.c. in the roof and typically doesn't have all edges blocked.

You could think about using the ceiling as a diaphragm but I'm not seeing any clear reason why you cant use the plywoood.