Sub floor for vinyl in bathroom

[SteUK]

Hi all,

Wonder if I might beg some advice.

Going to be laying new vinyl sheet flooring in my bathroom. Currently it has floorboard-thin hardboard-stick on vinyl tiles.

Naturally the thin hardboard (maybe 3mm) has suffered over the years and the floor is a bit up and down. Floorboards are as you would expect from a 60s council house. Average, but solid.

Am I correct in thinking I need to strip back to floorboard, lay 6mm plywood? If so, do I need structural plywood? 6mm expansion gap around edges, but what about between boards internally?

Thanks!

 

[foxhole]

6mm hardboard will do unless boards are really poor then use ply.