Correct places to use backer rod in nonrectangular rooms?

Which of these seams needs backer rod + caulking as opposed to just caulking? I attached a mock-up for illustrative purposes. I have flexible butyl caulking which is quite durable already, so I'm wondering which spots I should definitely do backer rod and which spots I'm fine with just caulking. Keep in mind the scale of this though. The big side wall sections are 4' sheets (8.5' high, 10' wide at middle). Drywall is only a single layer of 5/8". I thought I'd be fine to just use caulking for joint A which is a fairly mild splay (one side is an 8° splay while the rear is a 5° splay). Joint B (the most angled joint) are the ones I thought I should use backer rod for. I should also note that the room will float on carpet strips placed under the plates.. allowing it to be repositioned in the room it's in. This is for experimental & convenience purposes. The repositioning will be done carefully, and I'd like to think the butyl will be fine, but I'd like to know where backer rod is a must here! Should I also do the top perimeter of the walls where they meet the ceiling? Thanks! :)

Hi. Please read the forum rules for posting (click here). You seem to be missing a couple of things! :) I would put backer rod plus caulk on all of those, since there will be angled gaps at each joint. However, I'm kind of curious about how you came up with those angles and dimensions; that doesn't look like an optimal layout for RFZ, if that's what you were intending. - Stuart -

Soundman2020 wrote:

Hi. Please read the forum rules for posting (click here). You seem to be missing a couple of things! :) I would put backer rod plus caulk on all of those, since there will be angled gaps at each joint. However, I'm kind of curious about how you came up with those angles and dimensions; that doesn't look like an optimal layout for RFZ, if that's what you were intending.

Thanks for the heads up on all points :) I'll post a separate thread and we can dive into the details if you'd be so kind!

It's better to keep all your questions and posts together in one thread, so you can find things easily again in the future as you work through your build. If you want, change the title of the thread so it better reflects what you are trying to do. The problem when people spread out their questions over several threads is that you then lose track of what you asked where, and waste time trying to find it again later! Keeping everything about your build in one place makes it easier. - Stuart -