Applicability; Non-Residential Districts. No commercial, industrial, business, institutional, recreational, or educational use and no apartment, multiple or attached dwellings, municipal or school building, public utility structure, or parking lot, shall be constructed or externally enlarged, and no such use or structure shall be expanded or established in an building not theretofore used for such purposes, except in conformity with a site plan bearing an endorsement of approval by the Planning & Zoning Board.