N.J. Stat. Ann. § 46:10B-14

Graduated payment mortgages may be secured only by real estate on which there is erected or to be erected a structure containing one, two, three, four, five, or six dwelling units, a portion of which structure may be used for non-residential purposes, and interest thereon shall not exceed the usury rate established pursuant to R.S. 31:1-1 at any time during the term of the mortgage.