2"xps insulation under 4"conc floor ,help

[CapnAl]

I just picked up a bunch of 2" xps insulation to install under my 4" concrete floor. Do I need to put down any sand or anything else (besides the dirt) to get things nearly perfectly level or just a good dirt leveling, a vapor barrier, the 4x8 2" panels, and then the concrete? Do I need to use anything to seal the joints of the 4x8 panels, or is just keeping them tight to each other good enough? Vapor barrier goes where? Or what about 2 vapor barriers, one below the panels and one above??? Please advise. Any tips, suggestions, variations appreciated

 

[Slowgsr]

Base should be flat and compacted
Tape joints with tuck tape, 6mil poly on top, tape joints.

 

[rburke65]

I put my 6 mil vapor barrier on top on the compacted clay, then the 2", the my 6x6" mesh, pex, concrete. Good luck buddy!

 

[ScaldedDog]

Make sure those 4x8 insulation panels sit flat on the ground beneath them, with no air pockets. Otherwise, the floor will crack, no matter how much steel is in it.

Mark