Within the districts established by this chapter or by amendments that may later be adopted, there exist individually or in combination: non-conforming lots; non-conforming structures and non-conforming uses of land; which were lawful before this chapter was passed or amended, but which would be prohibited, regulated, or restricted under the terms of this chapter or future amendments. It is the intent of this chapter to permit these non-conforming uses to continue until they are removed, but not to encourage their survival. It is further the intent of this chapter that non-conforming uses shall not be enlarged upon, expanded or extended, nor be used as grounds for adding other structures or uses which are prohibited elsewhere in the same district. Illegal uses existing at the time this chapter is enacted shall not be validated by virtue of its enactment. Non-conforming uses are declared by this chapter to be incompatible with permitted uses in the districts in which such uses are located. A non-conforming use of a structure, a non-conforming use of land, or a non-conforming use of a structure and land in combination shall not be extended or enlarged after passage of this chapter by attachment on a building or premises of additional signs intended to be seen from off the premises, or by the addition of other uses of a nature which would be generally prohibited in the district in which such use is located. To avoid undue hardship, nothing in this chapter shall be deemed to require a change in the plans, construction, or designated use of any building or development on which actual construction was lawfully begun prior to the effective date of adoption or amendment of this chapter and upon which actual building construction has been carried on diligently. Where demolition or removal of an existing building has been substantially begun prior to rebuilding, such demolition or removal shall be deemed to be actual construction, provided that the work shall be carried on diligently. Actual construction is hereby defined at a minimum as having a valid ILP upon the initial passage of this chapter on date of passage of this Unified Development Ordinance.