Lot Coverage. The maximum lot coverage of all structures shall not exceed thirty-five percent of the total area of the lot or parcel. Notwithstanding, any lot or parcel with a required area of less than seven thousand square feet pursuant to this chapter may have lot coverage from thirty-five to no more than forty percent provided that all structures on the subject property do not exceed one story. For the purposes of this section, structural lot coverage shall include patio covers, trellises, carports or nonhabitable accessory structures, but not patio slabs, hardscape, driveways, swimming pools or spas, and shall be measured from the exterior walls and post for structures. For storage sheds, the provisions of Section 18.20.210 shall apply.