Is greenboard an acceptable plastic surround backer?

Question

I'm in Ohio, if that makes a difference for code.

In follow-up to Bathtub impersonating waterbed? , I ended up gutting the whole bathroom - the liner was not in great shape, there were layers and layers and layers of walls and tiles and who knows what. I'm now down to studs.

Currently looking at this surround: https://www.homedepot.com/p/Delta-Sturdifit-60-in-W-x-58-in-H-Five-Piece-Glue-Up-Tub-Surrounds-in-White-40194/204338527

In in installation instructions, it says to go over greenboard. I don't want to go against the instructions, but is greenboard acceptable? I've read a lot of things suggesting everything will leak, etc. If it's not greenboard, I'd worry it won't adhere correctly. If it is greenboard, I'm worried it'll rot in a few years.

Given that I'm currently at studs, what should I put between the studs and this surround? 2/3 walls in the tub alcove are internal, one is external. Should I do a moisture barrier everywhere in the bathroom, or just within the alcove? Should I do insulation in between studs? Greenboard on top, or cementboard?

As a final question, there's a soffit above the tub that I want to take down or at least replace (because it has evidence of moisture damage) - greenboard up there, or something else?

Thanks. Reading a lot of conflicting information, just frustrated.

Answer 1

i think you're ok with the green board, i like to use it everywhere in the bath to be safe but certainly in the tub area. Cement board is not needed as it isn't holding any weight (like tile). Ive installed these units and they work great as long as u caulk all seams. One thing I've learned the hard way is to use the recommended caulk as if its not correct it will peel out of the seams and be a pain. Silicone or acrylic latex sealant is not recommended. Use an advanced kitchen and bath polymer sealant for best results.As far as insulation, sure can't hurt if u are already down to the studs :-) Ds