All dwellings constructed after enactment of this Chapter shall include a garage capable of housing at least one car for a one-family dwelling so that at least one garage shall be available for each dwelling unit. Such garage shall have an interior dimension, (excluding columns) sufficient to provide for a parking space of not less than nine feet in width with a depth of 18 feet and shall otherwise conform to the requirements of all applicable provisions of all ordinances of the Borough of Paramus. Any existing dwelling which does not contain a garage as required above may be expanded, altered, reconstructed or converted without conforming to the above garage requirements, provided that such expansion, alteration, reconstruction or conversion does not exceed 25% of the floor area of the existing dwelling, whether such garage conforms to the requirements hereinabove or not, shall not be expanded, altered, reconstructed or converted so as to eliminate such existing garage. Nothing in this subsection shall be deemed to prohibit the expansion, alteration, reconstruction or conversion of an existing dwelling on a lot or lots containing an existing accessory building used as a garage and conforming to the above requirements.