I had to put on my rated safety glasses to read this thread. I wore gloves while typing.
I have to laugh at some of the comments, but I truly feel what Guy posted hits the mark. Follow the Z.
Jimmy, I think you posted a valid question. I'm also trying to imagine how thick the Z would be if it covered a protocol for all the potential structures we may encounter during tree work. I'd say, when we're doing tree work, the guidelines for tree work apply.
In all sincerity, I can think of numerous occasions in which I abseiled to a roof when doing tree work...especially following storm damage. Using the blower to clean up shingles, removing litter from gutters that resulted from our activity. I have yet to set up a system on which I'm tied into something other than a tree above the roof, but Jeff's post is great. I'll have to carry a few more options for rope protection now. :/