Removing marble tile floor for wood floor

[m7777777]

Hi, I have removed marble tile from my entry way for the purpose of putting wood floors down throughout the house. I didn't realize that 2 inches under the marble tile would be what seems to be a sand bed before getting to the cement foundation. For the sake of putting down a glue down wood floor on top, what do I need to do to that 2 inch bed after having removed the sand to prepare for putting down the wood flooring?

I've heard several different opinions so need some more please!

Thanks!
m7777777

[jadnashua]

I'm assuming that you need to build the floor up to keep the levels common? I guess it would depend on the actual height you need and how flat the slab is. Some more details might help formulate a path forward. I'd lean toward sleepers with a T&G ply subfloor, but it would depend on the results of the height buildup and flatness.