Ensuite chipboard floor sagging problem

[TheKeymeister]

I am about to start refitting my ensuite, and the floor is a bit saggy just inside the entrance door. I have had the ceiling down below for some plumbing work and the joint of 2 of the chipboard flooring sheets is just next to a joist and unsupported (see below pic)



First thought was to put a noggin in to support the joint, but I think after 20 years of being like that it won't fully cure it.

I then thought about replacing the whole floor with ply but it would be left with unsupported edges where the ply meets the chipboard of the next room. I could add noggins but there would be lots of them. And it would be a pain when the rest of the floor is ok.

Last thought was to chop out the dodgy unsupported section between the joists and let in a small piece of ply. No noggins required and minimum effort.

What are peoples thoughts on how to sort this out, I've no intention of tiling the floor, vinyl/lino/cushion floor much easier to change and less problems!

 

[John D v2.0]

Think carefully about whether you need to do anything, if you're increasing loads/traffic there or it's deteriorating already.
If you do want to do something small, personally I'd go for a few noggins across around 400 centres.
In my situation I pulled up all the floorboards and replaced with ply. This was partly because the wall was built on the floorboards and the floor had previously been cut out, leaving the wall floating, and partly to reduce deflection in the joists as they had been notched a lot

 

[TheKeymeister]

I finally got round to sorting this out tonight...

First off, chopped the dodgy section of floor out,


Added a bit more support (one more to go in top left corner once I've trimmed the strap back)


Drop in piece of ply, it's not the tightest fit admittedly, I'm calling it expansion gaps


It also allowed me to do some plumbing work, and I've got more to do in the future, so as long as it holds out it's been a great success

Also both the new piece of ply and the remaining chipboard round the edges will be screwed down once additional support has been fitted and plumbing work is complete.

 

[John D v2.0]

1 I can't zoom on your photos, upload to this site as photo bucket has some hosting protection going on.
2 are you sure that strap isn't lateral restraint for one of the walls? supposed to bridge over noggins between the joists as maybe the wall isn't thick enough to be independent all the way up
3. I can't see what your support is, and you must be restricted by all the pipes, but try to support the new ply on noggins rather than hanging it off the adjacent floorboards. it's easy to get creaks I found when cantilevering them off the side of the joist or other boards.