The ratio of the impervious coverage area to the upland lot area shall not exceed 75%. For oceanfront lots, the 75% calculation shall be made only on that area of the lot lying generally westward of the oceanfront building line. For the purposes of calculating impervious lot coverage, no portion of the lot which is mapped as wetlands, vehicular easements and no portion which is riparian shall be included in the calculation of determining permissible impervious lot coverage.