If any portion of the common elements encroaches upon any unit, or if any unit encroaches upon any portion of the common elements or any other unit as a result of the construction, repair, reconstruction, settlement or shifting of any building, a valid mutual easement shall exist in favor of the owners of the common elements and the respective unit owners involved to the extent of the encroachment. A valid easement shall not exist in favor of any owner who creates an encroachment by his intentional, wilful or negligent conduct or that of his agent.