Order characters numerically

It may be simple, but this SQL will order items numerically (1,2,3,10,20) instead of alpha (1,10,2,20,3).


SELECT ItemID, ItemName, ItemNum, CASE WHEN Len(ItemNum) = 0 THEN 'Z' ELSE SPACE(10- Len(ItemNum)) + ItemNum END OrderCol
FROM table
ORDER BY OrderCol