For all uses allowable in the "RH-O" Historic Townsite Residential Overlay District, the principal building and accessory buildings shall not cover more than 30% of the lot areas, excepting that, where a single lot of record, as defined in the definitions section of this Title, as of the effective date of the Title, has an area of not more than 7,500 square feet, the principal building and accessory buildings shall not cover more than 35% of the lot area. For all uses not allowable in the "RH-O" District, the lot coverage provisions of the parent district, if any, shall apply.