Hey folks,
starting monday i will be placing the sand bed with 300 feet of 3/4 pex on one inch of salvaged DOw styro.  My question is should the vapor barrier go below the foam or above the sand.  The building science web site noted a few months back in one of their emails that the barrier should be between the sand and concrete so the concrete would not lock in the moisture in the sand .  Since it will be practically impossible to keep the sand dry before the pour would it be ok to put down some 10 mil plastic under the foam and sand box and then another layer of 10 mil between the sand and concrete.  Wet sand would seem to be a better heat storage bed than a dry one. All help will be greatly appreciated.    The 3/4 pex will be for excess heat from the domestic hot water.  above that will be 5 inch concrete with 1/2 pex in two loops.  The footprint is only 20 by 28 and the basement walls are 10 inchs (Superior walls) thick so the sand bed will be small and shallow but hopefully not a complete waste of time and materials. It should be about 7 toms of sand.  Thanks for your time.  Michael