For mass zone, if the bottom level ref does not intersect, then this zone is going to be "not occupiable" and a warning is posted for it.

public static FailureDefinitionId NonOccupiableMassZone { get; }

Public Shared ReadOnly Property NonOccupiableMassZone As FailureDefinitionId
	Get

public:
static property FailureDefinitionId^ NonOccupiableMassZone {
	FailureDefinitionId^ get ();
}