rethinking bathroom floor - advice please

[jape]

Having read through a good many posts, bit confused!
Floor is old boards, 5 x 3/4 inch. Many split, cut, bits missing. Not nailed or screwed in places.

Area is length of bathroom 3100mm with width of around 900mm to edge of bath and boiler cupboard. Haven't investigated under the bath and cupboard yet.

Joists run length, 7x3 inch at approx 16 inch centres. 400mm.

So fixing down easy enough, then possibly 6mm dukkaboard if decide to tile.
Or an underlay for vinyl - is there one will absorb the gaps between boards and not show them through vinyl?

Other possibility I see on forum is replace with p5 chipboard across joists to nearest joist under bath.
Can I ceramic tile direct on this if I prime?

I see contrary posts on using plywood but also some recommend that over chipboard in bathrooms, some say ply is crap.

Is there a reasonably priced cement board or other at 18mm will span 400 mm as flooring? What about the 'no-more-ply' product straight on joists as flooring not just backing? If it comes that thick. More googling!

I am trying to avoid height difference so willing to use vinyl rather than ceramics but lass wants some 6mm nonslips she has seen, thus 18mm floor preferred as this also gives loo pan same fix height.

Sorry for questions, was going to just use 18mm p5 then prime and tile with flexible adhesive and 'waterproof' grout.
Until I started reading previous threads ...

[jape]

Wow. Some diy ers are crap. Assuming it wasn't tradies lol. The amount of rubbish under vinyl included washers, 2 screws, wood splinters, plaster drips and even a toothpaste cap at edge! Under floor boards was a bucketfull of bluey, a couple of dozen assorted nails including cut nails from a century ago and screws and loads of assorted crap.Only five of 20 odd boards were fixed solid. No pipes had clips or saddles and there are bare earth wires draped over .....

Decided on hardiefloor, it is structural as well as serving for ceramic tiling direct when lass saves up for wetroom next year. Seems joists are good and don't waver or wobble. Meanwhile cheap vinyl over and re-route plumbing chased into conduit up walls instead of through floor as present.

120 yr old terraces, you expect some crap. No sovereigns or gold bars yet.

Is there a worry about moisture differential now houses are central heated but under floor is moister. Noticed boards all cupped and shrunk. Polysheet under hardiefloor a good idea or bad for joists?

[kingnewport]

Personally I would replace the floor boards with way rock boards (today's floorboards) in 22 mm

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[jape]

Turns out joists and plumbing needs a fair bit of fixing. Going to use loose laid p5 for now with vinyl sheet over. Just so room can be used during renovation while future decisions made and saved for. Thanks.

[wine~o]

Turns out joists and plumbing needs a fair bit of fixing. Going to use loose laid p5 for now with vinyl sheet over. Just so room can be used during renovation while future decisions made and saved for. Thanks.

Loose laid could be an issue, at least a couple of screws per board would be needed; should be still easy to remove/replace as necessary.

[jape]

Loose laid could be an issue, at least a couple of screws per board would be needed; should be still easy to remove/replace as necessary.

Yup, understood, will do.