Matt wrote:
"nightjar" wrote:
If you are replacing the floorboards and want a flat floor, the simplest
answer is flooring quality chipboard.

Chipboard? Despite its wide use by crappy mass market builders, in an
extensive survey it was ranked just above cardboard, candy floss and
razor blades as the cheapest, nastiest and most unsuitable material
ever created for floors.

It can be very good, if you get moisture-resistant stuff, like
the stuff under my kitchen floor "tiles".