Curtain wall grid lines are outside wall. If you are trying to shorten the wall, please remove grid lines, including mullions on top of them.

public static FailureDefinitionId GridOutsideWall { get; }

Public Shared ReadOnly Property GridOutsideWall As FailureDefinitionId
	Get

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