Advice on plywood to cover floorboards

The floorboards in the flat I'm rennovating are about as can be expected for 200 year old floorboards (ie, not the smoothest and most level of floorboards).

I intend to overboard them with ply, but am looking for a bit of advice on the best ply to go for.

Most rooms will then have fairly thick underlay (as there's no other sound insulation between floors) and carpet on top. The kitchen and bathrooms will have rubber flooring.

A quick search of this forum (and other places) seems to suggest 6mm ply is best to use (there was a post somewhere on here from an employee of a rubber flooring company who also suggested 6mm for rubber flooring).

Is 6mm a good thickness to go with? What about 5.5mm, is this just as good, or should I see 6mm as a minimum (some places just seem to stock 6mm).

Also, what grade should I go for, there seem to be so many. I'm guessing marine is probably best for the bathroom, is this right? What about elsewhere? Shuttering ply seems the cheapest, and whilst I know this isn't it's intended use, as it just going to be covered up, will it still suffice, or should I go for a higher grade?

Thanks in advance for any advice.

Carpet in a bathroom? Not ideal. Screw 12mm WBP ply down and tile the bug.ger.

gcol said:

Carpet in a bathroom? Not ideal. Screw 12mm WBP ply down and tile the bug.ger.

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Luke said:

The kitchen and bathrooms will have rubber flooring

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I've just done the same job. 6mm ply nailed down with annular ringed 20mm nails. Ply was the cheapest the timber merchant had.
Carpet fitted in top and it seems fine. 6mm is everywhere and is usually price watched.

For a small ensuite with tiles I have done the same using 6mm but also bonded it with adhesive and PVA'd it. BUT you have to be sure the floor boards are sound to use 6mm.

Mine were rock solid and even with mosaics haven't seen a crack or creak in 18 months of heavy use.

Thanks for that.

Also, does anyone have any tips on measuring and marking up the ply boards so that they can be fitted against irregular walls?

As the property is about 200 years old, I'm guessing that the corners of the rooms aren't going to be all that square. What's the best technique for marking boards so that they can be cut to fit into the corners?