N.J. Stat. § 40A:21-14
Any ordinance adopted pursuant to the provisions of this act may also provide that an additional improvement, conversion or construction, completed on a property granted a previous exemption or abatement pursuant to this act during the period in which such previous exemption or abatement is in effect, shall be qualified for an exemption, or exemption and abatement, just as if such property had not received a previous exemption or abatement. In such case, the additional improvement, conversion or construction shall be considered as separate for the purposes of calculating exemptions and abatements pursuant to this act, except that the assessed value of any previous improvement, conversion or construction shall be added to the assessed valuation as it was prior to that improvement, conversion alteration or construction for the purpose of determining the assessed valuation of the property from which any additional abatement is to be subtracted. Unless provided by ordinance, no additional exemption or abatement shall be allowed.
N.J.S. § 40A:21-14