Any existing or proposed premises having more than 20,000 square feet gross floor area devoted to any use included in the Use Regulation Schedule under commercial and industrial uses shall be considered a major business complex. Any construction, alteration, relocation or change of use resulting in such complex shall be permitted only upon the granting of a special permit by the Planning Board. For the purposes of this subsection, "change of use" shall mean a change in principal use which results in or is accompanied by an increase in the gross floor area of the principal structure of 10% or the addition of at least 10 new parking spaces.