Roof Diaphragm connection to shear wall

[vobs]

I have a question regarding the load path from a near horizontal diaphrgam (slpoed roof) to an exterior shear wall, as in an eave condition. If the load is low enough, I specify and unblocked diaphragm and call out a Simpson connector to transfer the load from the trusses to the top plate. If the load is higher, I call out a blocked diaphragm, including the eaves. The problem then is to provide attic ventilation. I tell them to drill a couple of holes in the blocking and cover it with wire mesh. The contractor is having fits with this. Does any one else handle this differently? Thanks.

 

[JAE]

You could alternatively specify blocking in every other truss space where the blocking would extend from the roof sheathing down to the top plate.

But you don't want to leave the sheathing only connected to the staggered blocks but would rather have a continuous line of nailing to be consistent with the code tables for diaphram shear values.

So we use a short block piece in the open spaces where the short block is nailed to the roof sheathing but does not extend down to the top plate - leaving enough room for venting. The short pieces really don't work for you structurally unless you add strapping to tie the full blocks to the partial blocks - but this is expensive.

We usually check the shear in the diaphragm, using an added safety factor of two to account for the partial tie to the top plate.

The above is one option - we have also used the hole option that you describe above.

 

[DaveAtkins]

We use blocking in every other or every third truss space. I believe that if you have blocking spaced no more than 8' oc, you will have blocking at every sheet of OSB at the roof, and the diaphragm shear in each sheet can transfer to the wall top plate. YOU MUST PROVIDE ENOUGH NAILS INTO THE BLOCKING TO HANDLE THE APPROPRIATE SHEAR (for example, 6' of shear must be handled in a 2' length).

I have also used a vee shaped notch in the top of the blocking to allow ventilation, when the blocking must be continuous.

 

[rceng]

Why not just install the blocks flatwise? 2" nominal lumber provides enough penetration depth for design loads for 8d nails. The blocks over the plates (bird blocks) would of course be perpendicular to the rafters, drilled and screened (common practice), and may need connectors to transfer shear to the plates.