That is a great new feature of 8.2. You will want to use the Site:GroundDomain object, which has documentation in the IORef and EngRef. There are 3 example files packaged with 8.2 that use this object:object: - 5ZoneAirCooledWithCoupledInGradeSlab.idf - SlabInGradeWithInsulation.idf - SlabOnGradeWithInsulation.idf

In our development code, we have also implemented an integrated basement model, which made us rename that object to SIte:GroundDomain:Slab to differentiate it from the new SIte:GroundDomain:Basement. Keep an eye out for this in the next (8.3...) EnergyPlus release.