Townhouse demising wall at roof truss - need diagonal bracing?

[Ben29]

This is the architectural section though the 1-hour firewall (unit demising wall). Do I need to provide diagonal bracing as if this was the gable end at an exterior wall? (red lines illustrate diagonal bracing)

 

[phamENG]

I say yes. You don't have a load path through the wall for the bottom chord brace, so you need to get it back up to the roof diaphragm. The idea of the fire wall and independent lateral systems for each unit is to ensure that each unit can stand on its own in the event that the adjacent unit is lost. I see no difference here - if the adjacent unit is lost you want to make sure that the truss system remains stable.

 

[XR250]

The ceiling sheetrock is what braces the gable end in 99% of all residential structures.

 

[phamENG]

XR - fair point. We've had this (or a similar) discussion before. I say yes, but I also work in a high wind area where this sort of things matters. I've seen a handful of failures between the wall and gable end truss after high wind events where they aren't braced. Sort of like the "theoretical hinge" in a tall wall....I've seen the theory turn to reality and it's not usually very pretty.