Except as otherwise provided in this Article, the lawful use of land or buildings existing at the date of the adoption of this Ordinance may be continued even if such use of land or building does not conform to the regulations specified by this Ordinance, provided, however:

That no nonconforming lot shall be further reduced in size.

That no nonconforming building shall be enlarged, extended or increased, unless such enlargement would tend to reduce the degree of nonconformance, and except as provided in subsection § 31-501.4 hereof.

That no nonconforming use may be expanded.

That any single-family dwelling house which is in existence on the effective date of this Ordinance, but which has been rendered nonconforming by this Ordinance, either by reason or area or use, may be extended upon the same lot and may be altered, provided that the yard requirements of the S-50 Residential District are met, and accessory buildings to such an existing single-family dwelling house may be constructed on the same lot to the extent that such buildings are permitted in the S-50 Residential District.

That the limitations imposed by this Ordinance shall not prohibit the extension, enlargement, alteration, remodeling, repairing, or modernization of any dwelling, nor the construction, extension, enlargement, alteration, remodeling, repairing or modernization of a permitted building or structure accessory thereto in any Residential District existing at the effective date of this Ordinance which conforms to the Ordinance immediately superseded hereby, but which dwelling does not strictly conform to the requirements of this Ordinance, provided, however, that such extension, enlargement, alteration, remodeling, repairing, or modernization of such dwelling, or such construction, enlargement, alteration, remodeling, repairing, or modernization of such permitted accessory building or structure, as the case may be, does not itself create a violation of any of the provisions of this Ordinance, and provided, further, that no additional families or dwelling units are occasioned thereby.

If a nonconforming use of a building or land is abandoned, subsequent use of such building or land shall be in conformity with the provisions of this Ordinance.

A nonconforming use or structure existing at the effective date of this Ordinance may be restored or repaired in the event of partial destruction thereof.

Nothing in this Ordinance shall prevent strengthening or restoring to a safe condition any wall, floor, or roof which has been declared unsafe by the Construction Official.

No nonconforming use shall, if once changed into a conforming use, be changed back again to a nonconforming use.

Buildings may be erected on lots shown upon a subdivision plan at the effective date of this Ordinance, which are not of the required minimum area or width or on which the required open spaces cannot be easily provided, if such lots are included in a land subdivision and development plan which was either duly approved under the Municipal Planning Act of 1953, prior to the effective date of this Ordinance but subsequent to January 1, 1954, or which plan of subdivision was granted tentative approval under said Act prior to the effective date of this Ordinance but subsequent to January 1, 1954, and granted final approval after the effective date of this Ordinance but within three years from the date of such tentative approval.

Any parcel of land with an area or width less than that prescribed for a lot in the district in which such lot is located which parcel was under one ownership at the date of the adoption of this Ordinance and the owner thereof owns no adjoining land may be used as a lot for any purpose permitted in the district provided that all other regulations prescribed for the district by this Ordinance are compiled with, and further provided that no lot of less than 5,000 square feet in area or less than fifth (50) feet of frontage shall be so used.

Nothing herein contained shall require any change in plans, construction or designated use of a building for which a construction permit has been heretofore issued and the construction of which shall have been diligently prosecuted within three months of the date of such permit, and the ground story framework of which, including the second tier of beams, has been completed within six months of the date of the permit, and which entire building shall be completed according to such plans as filed within one year from the effective date of this Ordinance.

Except as otherwise herein provided, a nonconforming building may be altered but not enlarged or extended, unless said building is changed to a building conforming or more nearly conforming to the requirements of this Ordinance.

Nothing in this Ordinance shall be interpreted as authorization for or approval of the continuance of the use of a structure or premises in violation of zoning regulations in effect at the time of the effective date of this Ordinance.

The following procedure is to be followed where an owner of a building or use not in conformity with the provisions of this Ordinance seeks to establish that said building and/or use is a valid nonconforming building or use as defined in this Ordinance.

The Zoning Officer, if he be satisfied that said proofs tend to establish the existence of the valid nonconforming building or use, issue the Zoning Certificate, which shall specifically set forth any limitations established in connection with such nonconforming building or use. The proofs shall remain on file as permanent records of the Zoning Officer.

If the Zoning Officer, upon submission of the application and proofs to him, does not find that they tend to establish the validity thereof, then the application shall be denied and the applicant shall have the right to appeal such decision to the Board of Adjustment. (N.J.S.A. 40:55-D-70b)