N.Y. Comp. Codes R. & Regs. tit. 9, § 575.4 – Structures subject to building setback restrictions.

(a) The shoreline building setback restrictions apply to all principal buildings and to all accessory structures exceeding 100 square feet in size, including garages, sheds, porches, decks, barns, gazebos, guest cottages, tennis courts and permanent swimming pools, but not including boathouses or docks.
(b) Porches, decks and other structures attached to single family dwellings or to other structures subject to the building setback restrictions shall be considered part of the structure for purposes of applying the setback restriction.
(c) Decks or porches which are above water level and extend beyond the structural footprint of any boathouse, as that term is defined in section 570.3(c) of this Title, are subject to the shoreline setback restrictions if those portions which extend beyond the structural footprint exceed 100 square feet in the aggregate.
(d) Decks or patios which are not attached to another structure are subject to the building setback restrictions if they exceed 100 square feet, unless flush with natural ground level without raised elements such as railings or walls.
(e) Retaining walls shall be measured either in elevation (face) view or plan (top) view, whichever is larger.
(f) A retaining wall which is constructed of dry laid stone or untreated natural logs, and is smaller than 200 square feet in size, and does not exceed two feet in height above the mean high water mark, shall not be subject to the applicable shoreline setback requirements and variance procedures, provided that it:
1. (1) is designed to control an on-going erosion problem;
2. (2) is limited to the area necessary to control such erosion; and
3. (3) follows the existing natural elevation and contour of the shoreline.