Levelling floor prior to laying top LVT or Engineered wood

[Frazer G]

I have a problem that a previous owner knocked two rooms (lounge & dining) into one but did not match the floor height. The difference is about 30mm with the higher part being solid concrete and the lower part wood boards on joists. Some of the wood is a bit damaged so can't be used as a "finished" surface. My aim is to raise the lower part to be level with the concrete but 30mm is an awkward number. I have considered using battens on top of the existing and top the battens with 6mm ply. That would allow the existing floor to breath. The finish "topping flooring" has yet to be decided but will probably be LVT or engineered wood about 8 - 10mm which will run seamlessly (I hope) across both parts of the room. Ideally I would like a small amount of flexibility as the wood part may flex with different seasons, temperature etc. 

Any comments or observations would be most welcome.

[Mr Punter]

I don't know what the need for the floor to breathe is all about.  Suspended timber floors often had outside airflow under to help protect the timbers from rot.  I don't think the batten gap on the room side will do any good.  6mm ply is not stiff enough for a floor.

 

You could lay some thin 10mm XPS and overlay with chipboard.

[Conor]

If the wooden floor is lower, just use plyboard or chipboard screwed down. If it's 30mm, then a layer of 18mm and then 12mm should do the job. You might want to use som packing spacers where the floors meet to get it perfect.

[Frazer G]

Thanks for the replies. I have some concerns with just using plywood  as a packer as the floor below the existing wood floor area is soil. At the moment there is no sign of rot or other damp issues as there is plenty of air circulation. My concern is that I do not want to seal in the dampness which may be present. What are the views of the following suggestion? If I lay treated roofing batten across the existing floor (they are about 18mm in my local builders merchant) and then lay moisture resistant chipboard (again 12mm seems available but if not ply is) on top of the battens would that be adequate to support LVT flooring of failing that, engineered wood?

 

All opinions welcome please.

Edited October 3 by Frazer G