Thank you for your comments.

I distinguish between a) structural engineering, and b) legal regulatory issues.

a) Before designing the house, I made some effort to acquaint myself with structural issues. I'm not sure how earthquake/tsunami risks are assessed in residential construction on Massachusetts barrier islands. I concluded that hurricane/tornado hazards were relevant, and included the use of "hurricane ties" in securing the rafters, a precaution which Tim abandoned in the course of his construction because their installation required manually rather than machine driven nails.

With respect to lateral wind forces on the outside stairs, I suspect that these stairs are substantially protected by their close proximity to the 18 x 40 foot wall of the house to which the upper end of the stairs is tethered. I don't know to what footing, if any, the lower end of the stairs is attached. (Better not ask) Intuitively, I suspect that the chief wind hazards to the stairs are the upward airplane wing like forces which wind turbulence would exert on the 22 +- individual treads of the steps and on the platform at the top. These forces could be estimated by titrating the force of 80 m.p.h, 100 m.p.h and 120 m.p.h. winds e.g. against an aggregate horizontal surface of perhaps 4 x 20 = 80 sq.ft comparing this to the weight of the installation plus the tensile strength of steel rods and their associated brackets. The building inspector would require a professional engineering opinion. 

b) The esthetic legal regulatory issues are, as we know, purely political and social. The Historic District Commission (HDC) infers that its juridiction limited to structures visible from a public highway confers on it the authority to adjudicate all external appearances of such structures, even where, as in the case of our house for example, the muntins of divided lights on south facing windows are visible from a public highway by no stretch of the imagination. I doubt that even the fact that steel rods stabilizing the outside stairs would be invisible from six feet above the level of any highway including the Head of the Plains Road would deter the HDC from ordering their removal. Hence the hypothetically unavoidable confrontation with the HDC entails issues only of procedure but none of fact.