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How would you insulate between old and new slab?

Live in NY, I have a early 1900's carriage barn with about 4-6 inches of concrete with rebar, no vapor barrier (not sure when the floor was poured) No Cracks.
I took off the old barn doors and put on patio doors, raising them up 4 inches, (max I could get for headroom)
I'm going to install radiant and pour new concrete with color as a finished floor, just wondering what some opinions are here.
Insul tarp vs. plastic and foam vs other options for 4 inches of pour room.



  • nibs
    nibs Member Posts: 470
    Am in the process of pouring my slab, over my pex.
    Many people here much more knowledgeable than I however absent a site inspections, and assuming no vehicular loads, if the existing concrete is in good condition, I would lay a vapor barrier, taped at the joins, then 1.5 inch XPS styrofoam, with taped joins, staple 1/2 " pex to the foam then pour your slab using fiber and a super plasticizer for max strength, order your cement with 1/2" minus aggregate if poss. Do not saw cut the control joints use an insert. If you want to use bigger pex then you may want to use thinner insulation.