Plywood over plywood?

[kolt]

Hey, as usual looking for advice.

have a small area of 2sqm (1m X 2m). I removed old lino and plan to glue karndean, the problem is, have to raise a floor by about a cm to level it with next room. Current floor is chipboard with 9mm plywood screwed to it.
I can probably remove the 9mm ply and place 18mm, but wondered what are my alternatives.
Is it possible to put additional 9mm plywood on top and screw through both layers of ply into chipboard or it is a bad practice?
Or maybe selflevel to add a cm? if selflevel, will it be better to remove original 9mm ?
Thanks

 

[Deleted member 174758]

No problem adding an extra layer of plywood. Lay your sheets at right angles to the existing sheets, make sure that the joints overlap (i.e. not one directly above the one below) and that your screws are long enough to go into the chipboard but not through it (so c.35mm). Screw centres should be around 150mm as this prevents movement