SECTION 1.   Section 20 of Chapter 40B of the General Laws, as appearing in the 2008 Official Edition, is hereby amended by inserting after paragraph 1 the following new definition:-

“Adjunct apartment housing”, a separate housing unit, complete with its own sleeping, cooking, and sanitary facilities, that is substantially contained within the structure of a single family dwelling, but functions as a separate unit.

                SECTION 2.   Paragraph (4) of section 20 of Chapter 40B of the General Laws, as appearing in the 2008 Official Edition, is hereby amended by striking out the second sentence and inserting in place thereof the following new sentence:-

Requirements or regulations shall be consistent with local needs when imposed by a board of zoning appeals after a comprehensive hearing in a city or town where (1) any combination of low or moderate income housing and adjunct apartment housing, exists which is in excess of ten per cent of the housing units reported in the latest federal decennial census of the city or town or on sites comprising one and one half per cent or more of the total land area zoned for residential, commercial or industrial use or (2) the application before the board would result in the commencement of construction of such housing on sites comprising more than three tenths of one per cent of such land area or ten acres, whichever is larger, in any one calendar year; provided, however, that land area owned by the United States, the commonwealth or any political subdivision thereof, the metropolitan district commission or any public authority shall be excluded from the total land area referred to above when making such determination of consistency with local needs.

                SECTION 3.   Section 5 of Chapter 59 of the General Laws, as appearing in the 2008 Official Edition, is hereby amended by inserting after clause fifty-seventh the following new clauses:-

                Fifty-eighth. The increased value of residential real property as a result of alterations or improvements thereto, not to exceed a percentage of the taxes due as shall be determined by the city or town, resulting from alterations or improvements that are made to create an adjunct apartment which qualifies as low or moderate income housing pursuant to section 20 of chapter 40B. Any exemption granted pursuant to this clause shall terminate when the premises no longer meets the requirements of said section 20 of chapter 40B. This clause shall take effect upon its acceptance by any city or town and shall apply only to alterations or improvements made on or after the date of such acceptance by such city or town.

                Notwithstanding any provisions of this clause to the contrary, a city or town by vote of its town meeting, town council or city council with the approval of the mayor where required by law, may adopt and authorize exemptions from property taxes, in accordance with this clause, for a specified term not to exceed 15 years, for that portion of any parcel of real estate which is certified as an affordable adjunct apartment pursuant to section 20 of chapter 40B.