@palaka: i saw your previous post.
so your control room is in the house, so presumably that does not have a concrete roof like your tracking room, correct?
you can control echo by: 1) avoiding parallel surfaces (walls, ceiling/floor); 2) using absorbers; and 3) diffusers.
unless you live in a posh country home, remote from all the urban jungle noise, concrete alone may not be sufficient noise insulation. you may need additional layers--walls, ceiling/floor.
i would also recommend double doors to keep noise from seeping into your tracking room. additionally, you will need to treat your room's acoustics, which typically entails curtains, carpets, bass traps, diffusers, etc.
it all depends on the acoustic fidelity you are looking for--and, of course, the inescapable budget.