Hi,
We are planning replacing our floorboarded kitchen floor with
chipboard. The boards are in bad nick with being cut over the years
and lifted for electrics and heating. The joists are spaced at 40cm,
from middle to middle
so according to readers digest 18mm Chippy would be fine.

http://www.readersdigest.co.uk/diy/webpages/274_275.htm

I am wondering if 22mm would be better as I will have less packing out
to do, to bring the floor to the same level as the hall as the current
floorboards are around 25mm thick. Or should I stick to 18mm and use
something to pack it up to the height of hall?

It is a tenament 1st floor flat in case that makes a difference.

What are the best materials for packing, I was just going to use some
hardboard I have.

I am going for toungue and groove so I lay long edge across joists and
not need to make noggings.

Then I can put a layer of ply down and tile. Actually this will add
height, so should I worry too much about making the chipboard floor
match the hall floor height? Only issue would if there are any boards
in kitchen I can't lift there will be a height mismatch.

I am also hoping that once the chippy is screwed down, and level it
will stop the washing machine dancing across the kitchen.

Any tips most welcome :-)

tks