Single Family Zoning Ends In Charlestown (Updated)

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UPDATE: Although the Town Council did not make the changes the Planning Commission had strongly advised to limit ADUs to year-round use and to limit lot size, the Zoning Office is interpreting the ordinance in a way that does limit ADUs to year-round use and does limit the lot size to 20,000 square feet for non-family ADUs. There is still no minimum lot size for family ADUs. We have updated this post to reflect the Zoning Office’s January 25 memo.*


On January 8, the Charlestown Town Council, on a vote of 3-1 with Councilor Susan Cooper voting no,** adopted the one-size-fits-all state law regarding Accessory Dwelling Units (ADUs) by passing a new Zoning Ordinance that allows ADUs for both family and market-rate rental.

Charlestown is allowed by the state to change very little regarding ADUs, but the town could specify, for example, the residency of the property owner and the occupant of the ADU, limit the ADU to structures existing as of a certain date, and specify the maximum size of the ADU. The Planning Commission advised that these be explicitly specified in the ordinance.

The ordinance passed on January 8 could have allowed both types of ADUs to be added to nearly any residential lot in town, no matter how small, and allowed the new units to be used as short-term or seasonal rentals. However, on January 25, Charlestown’s Zoning Office interpreted the newly passed ordinance in a way that does limit ADUs to year-round use and does limit the lot size to 20,000 square feet for non-family ADUs. Family ADUs can be built on any residential lot in town, no matter how small; that is, they have no minimum lot size, except that which DEM might impose.

Until 2022, the Charlestown Zoning Ordinance provided for accessory dwelling units for family members attached to an owner-occupied, year-round home. These ordinances were invalidated by a state law enacted in June 2022, but that law allowed towns to adopt the state law (that is, “opt-in”), or not. The previous Town Council opted to wait for the legislature to change the law to better fit coastal towns, and that legislation is a priority for the state legislature, but the current Town Council has decided to opt in to the very flawed 2022 law rather than wait.

Some Highlights Of The January 8 Changes

ADU For Family Members:

  • A second dwelling unit is allowed on any lot within, or as an addition to, a legally established, owner-occupied residence where the ADU’s occupant(s) meets the state definition of a family member.
  • A family member defined by the state includes any related person, including, but not limited to, a child, parent, spouse, mother-in-law, father-in-law, grandparents, grandchildren, domestic partner, sibling, care recipient, or other member of the household such as caregivers, and employees.
  • The layout and size of the accessory dwelling unit can be up to two bedrooms and up to 900 square feet or 60% of the primary dwelling size, whichever is smaller. This is a 40% size increase over the town’s previous ordinance.
  • Any addition to the primary residence for the ADU would have to follow the Zoning Ordinance with respect to setbacks, etc., for primary structures.
  • There is no minimum lot size for family ADUs.***

ADU Not Restricted To Family Members:

  • A second dwelling unit may be a market-rate rental, is not restricted to family members, and is allowed in all residential zoning districts in Charlestown if the lot is at least 20,000 square feet in area.
  • The ADU must be located within the existing footprint of an existing principal, accessory, or detached structure.
  • The layout and size of the accessory dwelling unit can be up to two bedrooms and up to 900 square feet or 60% of the primary dwelling size, whichever is smaller, but the ADU must fit within the existing structure.
  • Because the principal, accessory, or detached structure is existing, it may be a legal non-conforming structure that is not in conformance with setbacks and other Zoning Ordinance requirements.
  • The existing accessory, or detached structure may be as close as 10 feet to neighboring property lines rather than the current 20 to 100 feet depending on the zoning district.
  • The second dwelling unit may be built in an existing principal, accessory, or detached structure located in a floodplain if the structure is legally non-conforming, even though current subdivision regulations do not allow a new lot to be created in a floodplain.

For Both Types Of ADU:

  • Although the number of bedrooms would be limited by septic system capacity, a second or larger system may be added if DEM allows.
  • The additional dwelling unit is intended for year-round occupancy and therefore should not be used for short-term rentals, such as those rented through Airbnb, but there is no penalty in the ordinance for doing so.
  • Existing, legal non-conforming lots and structures could add a second dwelling unit.
  • When a building permit to construct an ADU is pulled, the property owner must provide a signed affidavit stating that their principal residence is on the property, but they are not required to return at any point in the future to update the affidavit.
  • The property owner may occupy either the primary dwelling or the ADU.

At the January 8 public hearing, the Town Council declined to make changes the Planning Commission had proposed that would have provided some protection to the town’s groundwater and neighborhoods.

  • The ordinance as proposed and passed contains the following language “An ADU is intended for year-round occupancy or otherwise to be the primary residence of the person or persons who will occupy it regardless of family relationship to the property owner.” Concerned that the word “intended” may not be enforceable, the Planning Commission advised that this should be changed to “… intended for year-round occupancy and shall be the primary residence of the person ….”. This two-word change would have stopped vacation rentals in these new ADUs, but the change was rejected by the Town Council.
  • The ordinance states that “prior to the issuance of a building permit … the property owner has provided a signed affidavit stating that their principal residence is on the property”.  The Planning Commission proposed that this be changed to “the property owner has provided a signed affidavit stating that their principal residence is on the property and that the occupancy of the ADU will comply with § 218-53 A. The affidavit shall be recorded in the Land Evidence Records of the Town of Charlestown and shall be resubmitted and recorded on an annual basis.” The Planning Commission’s changes would have required that the property would continue to be owner-occupied in future years and when a property was sold. This change was also rejected by the Town Council, leaving open the possibility that in future years this restriction would be forgotten and the property could be sold for investment purposes with an absentee landlord.

This increase in overall housing density for Charlestown was passed without any assessment of the cumulative potential impacts of the increased septage on groundwater, drinking water, the coastal ponds, and other water bodies. Allowing any lot that can get DEM approval to create an additional dwelling unit will impact coastal areas especially.

*Zoning Office’s January 25 memo

** Councilor Cooper supported the ordinance changes that would once again allow ADUs for family members and others, but voted against the ordinance because the recommendations of the Planning Commission that would have provided better protection to the town were not included in the final version.

*** Some existing lots are so small or otherwise constrained that DEM or CRMC will not allow an increase in the number of bedrooms, for an ADU or any other purpose.

The banner image is an aerial photo of the West Beach area, where dense development already negatively impacts the coastal ponds and where ADUs will exacerbate those problems.