Just looking for some Opinions here.  When using 4' by 8' foam boards under a slab, is it better to stager the ends?  Also should the seams be sealed and if so, with what?

Thanks,

Ron Camerata

If you are using Crete-Heat you must stagger the joints

I'm not sure what you mean by Crete-Heat, but I'm using 1/2" pex stapled to 2" of foam board, in a 4" fiber concrete slab.

Start with 6mil. poly (clear plastic) for a proper vapor barrier, followed by XPS in any pattern. Taping is OK by unnecessary. Heat load analysis and ground water assessment determines the thickness.

Great, that's what I have. This is my first slabe instalation and I know it's hard to correct mistakes after the slab is poured.

Any opinion on how far from the outside walls the tubing should be placed?

Thanks,
Ron C

Ron, i just pour a slab with pex over 4 by 8 foam board. I staggered the joints and used duck tape to seal the joints. I did this to prevent any concrete that seeped between the foam from creating a thermal bridge down to the poly film on the gravel. Be careful placing your conctrete. I used a conveyor truck to save money but due to the drop the concrete knocked the pex all over the place. Rent a pump truck if you cant get the concrete chute close to the surface of the pour. Good luck

I used 2.4" styrofoam shiplapped and staggered all joints just so they held each other together while being walked on. Did not need to use tape. The styro I used was 2'x8'. I put poly underneath the foam. Then I put wire mesh over the foamboard and the plumbers tied the pex to the mesh with zipties. Then we pumped the concrete in with a hose off the pump truck. The plumbers did not put pex in the future boilerroom, around the future toilet wax ring and under the future bathtub. (I don't know why they skipped the bathtub area, anybody know?). Oh and the reason I used 2.4" was because I ordered 2" and 2.4" was delivered. I did not even know they made a 2.4" styrofoam.