I am looking to add insulation to a first room floor (100-year-old
farmhouse, full fieldstone basement underneath). Will be removing carpert
and pad (about an 1"), putting down laminate flooring, so have some room for
a layer of insulation.a

Is it possible to put a layer of foam board below a 1/4" layer of ply prior
to flooring? The basement is a rat's nest of wires and pipes. Maybe even a
simple layer of poly would make a huge difference?

FYI: I have already done the walls and sealed all cracked in them and around
pipes. New windows, etc. This is the last frontier.

Thanks.