Any building legally existing and any use lawfully made of land or buildings as of the effective date of the adoption or of any amendment of this bylaw and Zoning Map may be continued in the same location, to the same extent and for the same purpose and may be expanded, replaced or changed as permitted in this bylaw. A building for which a building permit has been issued prior to the publication of the first notice of the required public hearing on the adoption or amendment of this bylaw affecting such building shall be deemed to be an existing building, provided the construction thereof is commenced within six months of the permit being issued and proceeds in good faith to completion.

A nonconforming building or use may be changed so as to conform to the bylaw, but once made conforming no reversions to nonconforming status shall be permitted.

If a nonconforming use is discontinued for a period of 24 months or if a nonconforming building remains unused for 24 months, such use or building shall be deemed to have been abandoned and no resumption of the nonconforming status shall be permitted.

A dimensionally nonconforming building may be structurally repaired, altered, or extended, provided it is not thereby made nonconforming to a greater extent. A dimensionally nonconforming building damaged by fire or other natural causes may be reconstructed in the same location, provided that the damage does not exceed 75% of the market value of the building prior to such damage and that the reconstruction does not enlarge the volume enclosed by the building by more than 25% or make the building dimensionally more nonconforming, and provided further that the restoration work on such building commences within 12 months after such damage; otherwise the building may only be rebuilt so as to conform to this bylaw. Where the disagreement arises regarding the market value of a building so damaged between the Building Inspector and the owner, the latter may present the opinion of a professional real estate appraiser.

A nonconforming use may be changed, extended or altered only upon finding by the permit granting authority that such change, extension or alteration shall not be substantially more detrimental than the existing nonconforming use and is subject to such conditions and limitations as the Board of Appeals might impose. It is the intent of this subsection that such change of use be permitted by the Board of Appeals whenever the proposed use is of the same general class as the existing nonconforming use and will not significantly increase traffic, noise, bright lights, and other undesirable impacts on the surrounding environment. Except as provided in § 175-1.6 of this bylaw, in all cases where a change, extension or alteration is proposed for a nonconforming use or lot, approval from the Zoning Board of Appeals is required, including cases where the proposed change would also require a special permit from the Planning Board.

A nonconforming use may be expanded in size or scope of the activity within confines of the lot used therefor and to the extent permitted by the dimensional requirements for the district in which such nonconforming use is located.

Any nonconforming building that is unsafe or dangerous to the public by virtue of its location or structural condition, and any nonconforming use that is harmful, hazardous, noxious or offensive may be ordered to be made safe, discontinued, demolished, or closed as provided by law and notwithstanding the provisions of Subsection A of this section.

Nonconforming single- and two-family residential structures may be reconstructed, extended or altered as of right following a determination by the Building Commissioner that such reconstruction, extension or alteration does not increase the nonconforming nature of the structure, and does not increase the habitable floor area of the structure by more than 25%.

No increase in nonconforming nature. The reconstruction, extension or alteration of a single- or two-family residential structure that is described in any of the following circumstances shall not be deemed to increase the nonconforming nature of a structure:

Increase in nonconforming nature or increase in habitable floor area by 25% or more. In the event that the Building Commissioner determines that the reconstruction, extension or alteration of a nonconforming single- or two-family residential structure increases the nonconforming nature of the structure, or in the event that such reconstruction, extension or alteration increases the habitable floor area of the structure by 25% or more, a finding pursuant to MGL c. 40A, § 6 granted by the Board of Appeals shall be required to allow such reconstruction, extension or alteration. A determination may be granted by the Board of Appeals only if there is a finding by the Board of Appeals that the reconstruction, extension or alteration shall not be substantially more detrimental to the neighborhood in which the structure is located than the existing nonconforming structure.