Replacing bathroom floor after water damage

Hi all,

I have a bathroom floor, which consists of the following layers:
- Vinyl tiles
- Wooden underfloor (6mm ply)
- Chipboard (22m)
- Sound proofing plasterboard (17mm)
- Wooden battens with about 1cm of foam on the underside
- Wooden layer (not sure what but it is a little warped)

I live on a 3rd floor flat of a building built in 2007.

The only attached layers is the ply to the chipboard.

I have ripped up about a third of the floor because of water damage (the chipboard was just crumbling and the bottom wooden layer that the battens rested on is slightly warped so there is a dip where at the end where the soil pipe is (see pic).

I am planning on replacing the removed section like for like. Any ideas how to attach the new chipboard to the old? Or is it ok not to not attach it?

It seems strange that you've been on here since 2012, and haven't noticed the endless posts about remedial bathroom floors and water damage? Why not do some researching?
In the meantime, if you post a photo or two it would help.

Hi vinn, I've done some reading and further looking and updated my original post.