P5 chipboard on suspended floor

[Fit Pro]

Hi everyone,
I have a question regarding putting P5 moisture resistant chipboard on the suspended flooring of the ground floor. I've already done so on the first floor instead of flooring boards and was very happy with the outcome ( cost effective, even floor, no hassle). But I'm not sure about doing the same on the ground floor. The distanсe to the ground is 40 cm (16 inches) and the soil doesn't look wet at all. I also plan to put a frame of timber along the walls.
The old joists are rotten away (I assume it's because there was no damp proof under the laminate). 
So the question is if it's ok to put P5 chipboard on the ground floor and if so, can I use 18 mm ones or 22mm only?
 

[Mr Punter]

Yes you can fit 22mm P5 chipboard flooring to the ground floor joists.  Make sure all joists are sound and there is good airflow beneath.

[wozza]

I would insulate if its a ground floor - and as said above check your airflow / airbricks

[Fit Pro]

Thanks so much for the replies guys.
The previous joists mostly rotten from the top not from the bottom - I assume if I put the damp proof membrane between the newly installed joists and the chipboard it should be fine?