A. 
All multiple dwellings for residential use require a special permit from the Board of Appeals.
B. 
Uses, whether or not on the same parcel as activities permitted as a matter of right, accessory to activities permitted as a matter of right, which activities are necessary in connection with scientific research or scientific development or related production, may be permitted upon issuance of a special permit by the Planning Board, provided the Planning Board finds that the proposed accessory use does not derogate from the public good.
A. 
Applicability. This Zoning Bylaw shall not apply to structures or uses lawfully in existence or lawfully begun, or to a building or special permit issued before the first publication of notice of the public hearing required by MGL c. 40A, § 5, at which this bylaw, or any relevant part thereof, was adopted. Such prior, lawfully existing nonconforming uses and structures may continue, provided that no modification of the use or structure is accomplished, unless authorized hereunder.
B. 
Nonconforming uses. The Board of Appeals may grant a special permit to change a nonconforming use in accordance with this section only if it determines that such change or extension shall not be substantially more detrimental than the existing nonconforming use to the neighborhood. The following types of changes to nonconforming uses may be considered by the Board of Appeals:
(1) 
Change or substantial extension of the use;
(2) 
Change from one nonconforming use to another, less detrimental nonconforming use.
C. 
Nonconforming structures. The Board of Appeals may grant a special permit to reconstruct, extend, alter, or change a nonconforming structure in accordance with this section only if it determines that such reconstruction, extension, alternation or change shall not be substantially more detrimental than the existing nonconforming structure to the neighborhood. The following types of changes to nonconforming structures may be considered by the Board of Appeals:
(1) 
Reconstructed, extended or structurally changed;
(2) 
Altered to provide for a substantially different purpose or for the same purpose in a substantially different manner or to a substantially greater extent;
(3) 
Demolition and rebuilding thereafter, as set forth in Subsection G below.
D. 
Variance required. Except as provided in Subsection E below, the reconstruction, extension or structural change of a nonconforming structure in such a manner as to increase an existing nonconformity, or create a new nonconformity, including the extension of an exterior wall at or along the same nonconforming distance within a required yard, shall require the issuance of a variance from the Board of Appeals.
E. 
Nonconforming single- and two-family residential structures.
(1) 
Nonconforming single- and two-family residential structures may be reconstructed, extended, altered, or structurally changed upon a determination by the Building Commissioner that such proposed reconstruction, extension, alteration, or change does not increase the nonconforming nature of said structure. The following circumstances shall not be deemed to increase the nonconforming nature of said structure:
(a) 
Alteration to a structure on a lot with insufficient area which complies with all current setback, yard, building coverage and building height requirements, where the alteration will also comply with all of said current requirements.
(b) 
Alteration to a structure on a lot with insufficient frontage which complies with all current setback, yard, building coverage, and building height requirements, where the alteration will also comply with all of said current requirements.
(c) 
Alteration to a structure which encroaches upon one or more required yard or setback areas, where the alteration will comply with all current setback, yard, building coverage and building height requirements.
(d) 
Alteration to the side or face of a structure which encroaches upon a required yard or setback area, where the alteration will not encroach upon such area to a distance greater than the existing structure.
(e) 
Alteration to a nonconforming structure which will not increase the footprint of the existing structure, provided that existing height restrictions shall not be exceeded.
(2) 
In the event that the Building Inspector determines that the nonconforming nature of such structure would be increased by the proposed reconstruction, extension, alteration, or change, the Board of Appeals may, by special permit, allow such reconstruction, extension, alteration, or change where it determines that the proposed modification will not be substantially more detrimental than the existing nonconforming structure to the neighborhood.
F. 
Abandonment or nonuse. A nonconforming use or structure which has been abandoned, or not used for a period of two years, shall lose its protected status and be subject to all of the provisions of this bylaw.
G. 
Catastrophe or demolition. Any nonconforming structure may be reconstructed after a fire, explosion or other catastrophe, or after demolition, provided that such reconstruction is completed within 12 months after such catastrophe or after voluntary demolition, and provided that the building(s) as reconstructed shall be only as great in volume or area as the original nonconforming structure and located on the original building footprint, unless a larger volume or area or a new building footprint is authorized by special permit from the Board of Appeals. Such time for reconstruction may be extended by the Board of Appeals for good cause.
H. 
Reversion to nonconformity. No nonconforming use shall, if changed to a conforming use, revert to a nonconforming use.