Mass. Gen. Laws ch. 143 § 3Z
Notwithstanding the provisions of any general or special law to the contrary, in any city, town or district which accepts the provisions of this section, any part time inspector of buildings, building commissioner, local inspector or alternate inspector may practice for hire or engage in the business for which he is certified, licensed or registered under the building code, while serving as such inspector; provided, however, that within the area over which he has jurisdiction as inspector or alternate inspector, he shall not exercise any of his powers and duties as such inspector, including those of enforcement officer of the state building code for the construction, reconstruction, alteration, repair, demolition or removal work done by himself, his employer, employee or one employed with him.
The inspection of such work shall be performed by the inspector of buildings or building commissioner of another city, town or district or by a special assistant inspector of buildings or assistant building commissioner who is appointed solely for the purpose of performing such inspections by the mayor of a city, the board of selectmen of a town or the governing board of a district.
This section shall take effect in a city, town or district upon its acceptance in a city, by the vote of the city council, subject to the provisions of the charter of such city; in a town, by a vote of town meeting; in a municipality having a town council form of government, by a vote of the town council, subject to the provisions of the charter of such municipality; and in a district, by the vote of the cities and towns of the district.
Mass. Gen. Laws ch. 143, § 3Z