Revisions to ADU Bylaw in the Works

Zoning Bylaw Fix Will Go to Public Hearing with Community Resources Committee and Planning Board

At its September 28 meeting, Town Council is expected to discuss and refer the planning staff’s proposed revisions to the town’s accessory dwelling unit (ADU) bylaw to the Community Resources Committee (CRC) and the Planning Board for a joint public hearing ahead of its final decision on the revised bylaw. . The proposed changes for Protected Use ADUs (PADUs) include Section 5.0112, Gross Floor Area; Section 6.18, Minimum or Maximum Floors; and Article 12, defining an attic as unfinished space. The existing bylaw does not define an attic. These fixes are meant to cap the living space in protected ADUs at 900 square feet, as specified in state law. A second type of ADU, a local ADU, can be 1200 square feet, but either the ADU or the principal dwelling must be owner-occupied.

After the state law allowed PADUs with minimal constraints, Amherst predictably saw a boom in ADU construction. However, concerns were raised that some of these structures had a second floor with two bedrooms and a bathroom, making the living space nearly 1200 square feet. These larger units were allowed because the building commissioner considered the second floor to be an attic, which was excluded from the gross floor area.

After neighbors objected, the issue went to the Zoning Board of Appeals, which denied the extra living space, stating that counting the second-floor living space as an attic went against the intentions of the law. The builder has taken the case to Land Court, where it is still pending.

Once the Planning Board posts the public hearing date, the current zoning will be frozen, and no additional PADU building permit applications will be accepted or certificates of occupancy issued until after the council’s final vote on the proposed zoning bylaw amendment (following the Planning Board and the CRC public hearings).

According to Building Commissioner Rob Morra, 23 applications for permits to construct PADUs have been submitted since the new bylaw went into effect in December 2025. Only 16 applications were submitted in the previous nine months. One builder, Michael MacDonald of MSM Builders, is listed on 12 of the applications. It is not known how many of these applications include the controversial finished second floor. An additional two proposed PADUs on two Lincoln Avenue properties owned by Yu-Pan Tzeng are pending approval by the Local Historic District Commission.

Proposed ADU Zoning Amendments from the Town Manager and Planning Director

The five proposed amendments regarding PADUs are:

1. Gross Floor Area: The sum of all floor areas of all stories or floors of the building of compliant ceiling height pursuant to the Building Code, including basements, lofts, and intermediate floored tiers, measured from the interior faces of exterior walls or from the centerline of walls separating buildings or dwelling units but, provided that for the purpose of calculating the GFA of any ADU, GFA shall exclude crawl spaces, garage areas, attics, enclosed porches, and similar spaces. Where there are multiple Principal Dwellings on the Lot, the GFA of the largest Principal Dwelling shall be used for determining the maximum size of a Protected Use ADU. [The document notes that the state is also considering changing how GFA is calculated.]

2. Minimum or Maximum Floors: A floor or story in a residential or non-residential building shall be considered to be that portion of a building, other than a half-story in a top floor or basement, between any floor and the ceiling or roof next above it, as measured under the Massachusetts Building Code.

3. Half-Story: A half-story in a top floor shall be any space primarily within the volume of a pitched roof, whether unfinished or finished to include Habitable Space, with required means of access and egress and in which minimum ceiling height and room dimensions exist in accordance with the Massachusetts Building Code and with a floor area but no l more than one- half of the floor area of the full story or space below.

4. Basement half-story: A half-story in a basement shall be any space, whether unfinished or finished to include Habitable Space, with required means of access and egress and in which a minimum ceiling height exists in accordance with the Massachusetts Building Code where more than half of the habitable space floor area is located above the average finished grade of the exterior of the building.

1. Definition of an attic: An attic shall be any space above the ceiling of a story or half-story, or any space behind a wall in the eaves of a roof that does not have the required ceiling height and room dimensions in accordance with the Massachusetts Building Code to be utilized as Habitable Space.