Length of rafter between torsional restraints

[MegKCB]

Hi All
Please could someone help me figure out the effective length (Lz) between torsional restraints of a rafter?
Is it between purlins? Or haunches? Is it different for downward and upward loading? I am beyond confused.
Thanks!

 

[KootK]

Is it between purlins?

Only between purlins that have kickers/fly bracing.

Or haunches?

Those will normally be considered points of torsional bracing.

Is it different for downward and upward loading?

It's usually the same.

Note that I'm flying a bit blind on this, not having much detail on your structure. So take my advice with a grain of salt.