I recently encountered the question: "if my property straddles the line that marks the boundary of the shoreline buffer, to what extent will future development be impacted by shoreline regulations?"
The leading case is Weyerhaeuser v. King County, 91 Wn.2d 721 (1979), wherein the court held:
We recognize that logging practices on lands adjacent to a shoreline may be regulated by means of the Master Program... Furthermore, the intended use of adjacent lands should be considered when taking any action under the SMA in order to achieve the coordinated development of the shorelines which is the object of the SMA... Direct authority to regulate uses of lands adjacent to shorelines is limited in the SMA, however, to the function of land use planning. Only those developments within the shorelines are subject to regulation by permits. The Board's determination that logging practices outside the shoreline cannot be regulated by means of substantial development permits for developments within the shoreline accords, then, with the structure and language of the statute.
So, practices outside the shoreline may be subject to limited regulation, but not by means of the permit. Of course, subsequent Shoreline Hearings Board decisions have raised all sorts of issues affecting how this rule is to be applied in the context of a particular development. Few developments bisected by the shoreline border will be susceptible to a simple analysis and anyone undertaking development on such a property would be well advised to undertake a careful review of the legal precedent as it may apply in their particular context.