1.   Every person in charge of an improvement on a locally-designated historic site or in an historic district shall keep in good repair all of the exterior portions of such improvement and all interior portions which, if not so maintained, may cause, or tend to cause, the exterior portions of such improvement to fall into a state of disrepair. This section shall be in addition to all other provisions of law, local ordinance or codes requiring buildings or structures to be well maintained.
   2.   Insofar as they are applicable to an historic landmark, historic site or improvement in an historic district, any provision of any adopted Model Construction Codes may be varied or waived, on application, by the Municipal Building Inspector; provided, that, such variance or waiver does not endanger public health or safety.
   3.   Nothing contained in this chapter shall prohibit the construction, reconstruction, alteration, demolition or any improvement on an historic site or in an historic district, pursuant to written order of any federal or state agency or pursuant to any court judgment to remedy conditions determined to be dangerous to life or health. In such case, no approval from the Preservation Commission shall be required.