chipboard floor. tile prep question

Previous builders made quite a few cuts into the chipboard floor. (See photo)

I was planning to just have hardiebacker which I have already purchased. However there is slight creaking indicating a bit of movement. Would you recommend ply as well as the Hardie backer?

I'm happy to do it as just want to ensure a solid surface but do you guys think its required or over the top?

 

What you need to do depends on why the Chipboard is creaking - are the joists underneath flexing? Or is it that the cuts aren't supported?

Best approach would be to fix whatever's making it flex & then go over with the Hardie backer - or trash the Chipboard & replace with 18/22 mm Ply & hardie on top.

 

best preparation of chipboard is to pull it up and put on bonfire.

 

Thanks for the replies. Joists seem OK at 400 centres.
I have added a few more screw's avoiding the pipes and it seems to improve it. I reckon I'll add a load of adhesive then lay down my hardieboard. Hopefully that will be sufficient

 

as long as the subfloor is secured hardie is very good stuff. you'll notice the difference as soon as you lay it