Hamilton

• ADUs are permitted by right in all four Hamilton zoning districts (R-1A, R-1B, RA, B) following adoption of bylaw amendments on January 28, 2025.
• The Building Commissioner is the permit-granting authority -- no special permit or ZBA review is required.
• Maximum size is 900 sq ft or 50% of the principal dwelling's gross floor area, whichever is smaller, with a cap of 2 bedrooms and 1 bathroom.
• Short-term rentals are prohibited in ADUs. Separate ownership (condominiumization) is not allowed.
• Properties in the Hamilton Historic District must comply with Historic District Bylaw (Chapter XXXI) including review by the Historic District Commission for exterior alterations.

1. Prepare application materials: Building permit application, certified plot plan, and elevations depicting all building facades with exterior materials.
2. Demonstrate compliance: Application must show clear compliance with Section 3.6 of the Zoning Bylaw, the Building Code, and all other applicable requirements including Hamilton Historic District regulations if applicable.
3. Submit to Building Commissioner: The Building Commissioner is the permit-granting authority for standard ADUs meeting all requirements of Section 3.6.
4. Site Plan Review (if applicable): A detached ADU proposed in the front yard requires Site Plan Review approval by the Planning Board. A second curb cut also requires Site Plan Review.
5. Historic District Review (if applicable): ADUs in the Hamilton Historic District requiring exterior alterations must meet Historic District Bylaw (Chapter XXXI) requirements and obtain approval from the Historic District Commission.

• Maximum size: 900 square feet of gross floor area or 50% of the gross floor area of the principal dwelling, whichever is smaller.
• Maximum bedrooms: 2
• Maximum bathrooms: 1
• Foundation: Must have a permanent foundation; no trailers or recreational vehicles permitted.
• Attached ADU design: Must maintain the appearance and essential character of the principal dwelling, specifically with respect to building height, compatible roof pitch, and choice of building materials.
• Entrance location (attached): Any new outside entrance must be on the side or rear of the principal dwelling.
• Dimensional requirements: Must meet Section 4.1.2 Table of Dimensional Regulations including maximum building height, maximum number of stories, maximum building coverage, and minimum front/side/rear yards. Attached ADUs must meet the setback requirements for the principal dwelling.
• Appurtenant structures: Porches, decks, and similar structures serving the ADU that do not count toward maximum gross floor area are limited to 150 sq ft combined.
• Pool and garage: No more than one pool and one garage (including the garage structure) on any lot with an ADU.

• Parking: One off-street parking space is required per ADU, consistent with the state law maximum.
• Curb cuts: No additional curb cut is authorized unless the lot configuration does not reasonably allow for a shared driveway. Applications proposing a second curb cut require Site Plan Review by the Planning Board.
• Transit exemption: Not specified in the local bylaw beyond state law defaults.

• Historic District: ADUs proposed in the Hamilton Historic District that require exterior alterations must meet all applicable requirements of the Historic District Bylaw (Chapter XXXI), including review and approval by the Historic District Commission.
• Front yard detached ADUs: A detached ADU proposed in the front yard requires Site Plan Review approval by the Planning Board.
• Single-family lots only: ADUs are only permitted on lots containing a single-family dwelling. Not permitted on lots with two-family, semi-attached, townhouse, three-family, or multi-family dwellings.
• One ADU per lot: Only one ADU is permitted per lot.
• No separate ownership: The ADU cannot be held in or transferred into separate ownership from the principal dwelling.
• Street address: ADU must have its own street address per state ADU Regulations.

Memorandum

To: Hamilton Planning Board From: Mark Connors, Planning Director Re: Proposed Amendments to Section 3.0 of the Hamilton Zoning Bylaw Date: January 28, 2025

On January 28, the Town received comments from the Town's legal counsel regarding proposed amendments to the Zoning Bylaw to accommodate changes in state law associated with Accessory Dwelling Units. The Commonwealth will not finalize its ADU Regulations until January 31, 2025, so further revision may be required.

Key Revisions in This Draft:

1. References to "large accessory dwelling units" removed (state clarified municipality not required to permit second ADU on single-family lot)
2. Section 3.6.2 broken into two sections (per Building Inspector feedback)
3. Section 3.6.4 (Required Application Materials) simplified per legal counsel
4. Regulations requiring ADUs to be "consistent with neighborhood character" deleted per legal counsel (modified to apply to attached ADUs only -- consistency with principal dwelling)
5. General prohibition on new curb cuts modified -- pathway for approval if lot configuration doesn't reasonably provide for shared driveway (second curb cut needs Site Plan Approval)
6. Restrictions on detached ADUs in front yard modified -- allowance only with Site Plan Approval
7. Common floor/ceiling and wall connector requirements removed per legal counsel
8. Definitions for Gross Floor Area and ADU revised per state regulation changes (Jan 17, 2025)
9. Street address requirements modified per state ADU Regulations

Table of Use Regulations (Section 3.0)

Y = Allowed by right; ZBA = Zoning Board of Appeals special permit; PB = Planning Board special permit/Site Plan Review

Section 3.4 - Conversion for Temporary Additional Living Area

[ENTIRE SECTION DELETED - RESERVED]

(Previously allowed temporary family living areas by special permit)

Section 3.6 - Accessory Dwelling Units

3.6.1. Purpose.

The intent of this Section is to permit an Accessory Dwelling Units (see Section 11.0, Definitions) on a Lot that contains a single-family dwelling unit (hereinafter referred to as the Principal Dwelling unit) for the following purposes:

1. Add moderately-priced rental units to the housing stock to meet the needs of small households, both young and old;

2. Make housing units available to moderate-income households who might otherwise have difficulty finding housing in the Hamilton;

3. Provide homeowners with a means of obtaining rental income, companionship, security, and services, and thereby enabling them to stay more comfortably in homes and neighborhoods they might otherwise be forced to leave; and

4. Provide more diverse housing options in the community in a manner that does not conflict with the residential character of single-family neighborhoods.

3.6.2. Permit Granting Authority.

The Building Commissioner shall be the permit-granting authority for Accessory Dwelling Units provided that the application meets the minimum requirements of this Section.

3.6.3. Where Permitted.

An Accessory Dwelling Units shall be permitted by right in all zoning districts where single-family dwellings are a permitted use provided that the Accessory Dwelling Unit meets the minimum requirements of this Section. Accessory Dwelling Units may be attached to the Principal Dwelling unit (hereafter referred to as an Attached Accessory Dwelling) or located in a separate accessory structure (hereafter referred to as a Detached Accessory Dwelling Unit).

3.6.4. Required Application Materials for Accessory Dwelling Units.

An Application for a building permit to construct an Accessory Dwelling Unit must include the following minimum materials:

1. A Building Permit application showing clear compliance with the requirements of this Section of the Bylaw, the Building Code, and all other applicable requirements, including, but not limited to, those governing the Hamilton Historic District.

2. A Certified Plot Plan demonstrating compliance the Zoning Bylaw and all other applicable codes and regulations.

3. Elevations depicting all building facades of the Accessory Dwelling Unit. The elevations shall include all exterior building materials.

3.6.5. Requirements.

1. Only one Accessory Dwelling Unit shall be permitted on each Lot containing a single-family dwelling. Accessory Dwelling Units shall not be permitted on Lots that contain a Two-family Dwelling, a Semi-attached Dwelling, a Townhouse Dwelling, a Three-family Dwelling, or a Multi-family Dwelling (see Section 11.0, Definitions), or any other form of housing apart from a Principal Dwelling unit.

2. An Accessory Dwelling Unit shall contain no more than two (2) bedrooms and one (1) bathroom and shall not exceed 50 percent of the Gross Floor Area of the Principal Dwelling unit or 900 square feet of Gross Floor Area, whichever is smaller.

3. An Accessory Dwelling Unit shall meet the applicable dimensional requirements set forth in Section 4.1.2, Table of Dimensional Regulations, including for Maximum Building Height, Maximum Number of Stories, Maximum Building Coverage, and Minimum Front, Side and Rear yards, except as stipulated in this Section. When attached to a Principal Dwelling unit, the Attached Accessory Dwelling Unit shall meet the required setback requirements for the Principal Dwelling unit.

4. An Accessory Dwelling Unit must have a permanent foundation; no trailers or recreational vehicles shall be permitted to serve as such a use.

5. An Attached Accessory Dwelling Units shall maintain the appearance and essential character of the Principal Dwelling unit, specifically with respect to building height, compatible roof pitch, and choice of building materials.

6. A Detached Accessory Dwelling Unit proposed in the Front Yard (as defined under Section 11.0, Definitions) shall require Site Plan Review approval by the Planning Board.

7. The location of any new outside entrance to serve an Attached Accessory Dwelling Unit shall be located on the side or in the rear of the Principal Dwelling unit.

8. Appurtenant uses exclusively serving an Accessory Dwelling Unit that do not count toward the maximum Gross Floor Area, including porches, decks, and similar structures, shall be limited to a combined total size of no more than one hundred and fifty (150) square-feet in area.

9. The Accessory Dwelling Unit shall not be held in, or transferred into separate ownership from, the Principal Dwelling unit.

10. One off-street parking space per ADU, consistent with state law maximum.

11. Septic/sanitary disposal compliance with Board of Health and Title 5.

12. No additional curb cut shall be authorized for access to serve an Accessory Dwelling Unit unless necessary because the configuration of the lot does not reasonably provide for an ADU with a shared driveway. Applications where a second curb cut is proposed to serve an Accessory Dwelling Unit shall require Site Plan Review by the Planning Board.

13. Street address requirements per state ADU Regulations.

14. [Annual compliance certification removed per legal counsel.]

15. There shall be no more than one pool and not more than one structure including a garage on any lot with an Accessory Dwelling Unit.

16. Short term rentals as defined in G.L. c. 64G, Section 1 are prohibited in Accessory Dwelling Units.

17. An Accessory Dwelling Unit proposed in the Hamilton Historic District, which requires exterior alterations, shall meet all the applicable requirements of the Historic District Bylaw (Chapter XXXI) including review and approval by the Historic District Commission if necessary.

Section 3.7 - Accessory Apartments on Large Lots

[ENTIRE SECTION DELETED / REPLACED]

(Previously allowed accessory apartments on lots greater than 10 acres by ZBA special permit. Now replaced with "Large Accessory Dwelling Unit" requiring Planning Board approval -- see Use Table.)

Section 11.0 - Definitions (New/Amended)

Accessory Dwelling Unit: A self-contained housing unit, inclusive of sleeping, cooking and sanitary facilities on the same Lot as a principal dwelling, subject to otherwise applicable dimensional and parking requirements, that: (i) maintains a separate entrance, either directly from the outside or through an entry hall or corridor shared with the principal dwelling sufficient to meet the requirements of the Building Code for safe egress; (ii) is not larger in gross floor area than 1/2 the gross floor area of the principal dwelling or 900 square feet, whichever is smaller; and (iii) is subject to such additional restrictions as may be imposed by a municipality, including, but not limited to, additional size restrictions and restrictions or prohibitions on short term rental, as defined in G.L. c. 64G, Section 1, provided, however, that no municipality shall unreasonably restrict the creation or rental of an Accessory Dwelling Unit that is not a short-term rental.

Gross Floor Area: The sum of the horizontal areas of the floors of a building measured from the exterior face of exterior walls. The Gross Floor Area of the Principal Dwelling shall be used for determining the maximum size of a Protected Use ADU.

Ownership: The individual(s) or entity, such as a trust, limited liability company, or corporation, in whom record title is held.

Second Memorandum

To: Hamilton Select Board From: Marnie Crouch, Chair, Hamilton Planning Board Re: Proposed Amendments to Section 3.0 of the Hamilton Zoning Bylaw Date: January, 2025

Background:

On August 6, 2024, the Governor signed into law Chapter 150 of the Acts of 2024, "An Act relative to the Affordable Homes Act" (the "Act"), which amends the Zoning Act, G.L. c. 40A. The new ADU provisions in Section 8 of the Act will take effect on February 2, 2025, 180 days following the date on which the Act was enacted.

The Act:

• Creates a statewide definition of ADUs
• Makes ADUs "as of right" in every city and town
• Supersedes any existing inconsistent local bylaws
• Removes ability to impose owner occupancy requirements on ADUs or principal dwellings
• Affirms ability to regulate or prohibit short-term rental of ADUs
• Clarifies square footage reference applies to Gross Floor Area

Hamilton has adopted the Stretch Energy Code. A certified HERS Rater is required for all new construction, including ADUs.

Your ADU must achieve a HERS index of 52 or lower (mixed-fuel) or 55 or lower (all-electric). Going all-electric earns a 3-point offset, making compliance easier. Budget $500–$1,500 for HERS testing.

ERV/HRV mechanical ventilation is now required (bath fans alone don't qualify). If on-site parking is provided, EV-ready wiring is also required.

The following local provisions have been preempted by the Massachusetts Affordable Homes Act (Chapter 150 of the Acts of 2024) and 760 CMR 71.00:

• Owner occupancy: Hamilton's previous bylaw required the owner to reside in one of the units. This is no longer permitted under state law.
• Special permit requirement: ADUs previously required a ZBA special permit. State law mandates by-right approval for the first ADU on a single-family lot.
• Existing building restriction: Hamilton previously only allowed accessory apartments within existing buildings. State law permits attached, detached, and internal ADUs.
• Neighborhood character standard: The previous requirement that ADUs be "consistent with neighborhood character" was deleted per legal counsel; the revised bylaw only requires attached ADUs to be consistent with the principal dwelling.

Hamilton proactively adopted bylaw amendments (January 28, 2025) to align local regulations with state law while adding permissible local guardrails (bedroom/bathroom limits, STR prohibition, historic district review, pool/garage limits).

• Hamilton ADU Bylaw Amendments (January 28, 2025): https://hamiltonma.gov/wp-content/uploads/2025/01/ADU-Bylaw-Amendments-1.28.2025.pdf
• Hamilton Full Zoning Bylaws: https://hamiltonma.gov/wp-content/uploads/2025/10/Zoning-Bylaws.pdf
• Town of Hamilton website: https://hamiltonma.gov
• Massachusetts Affordable Homes Act (H.4977 / St. 2024, c. 150)
• 760 CMR 71.00 (Protected Use Accessory Dwelling Units)