Substantial improvements, including first placement of permanent construction of a principal building on a site, such as the pouring of slabs or footings, the installation of piles, the construction of columns, any work beyond the stage of excavation. Permanent construction does not include land preparation, such as clearing, grading and filling, the installation of streets and/or walkways, excavation for a basement, footings, piers, foundations, the erection of temporary forms, nor installation on the property of accessory structures, such as garages or sheds not occupied as dwelling units or not part of the principal building. For a substantial improvement or addition to an existing structure, the actual start of construction means the first alteration of any wall, ceiling, floor, or other structural part of a building, whether or not that alteration affects the external dimensions of the building. [Ord. 1267, 09-14-09.]