STEVE FELDMAN

BETH DAVIS

Can a second mortgage fund your Accessory Dwelling Unit?

Eligible Massachusetts homeowners can secure a fixed-rate second mortgage up to $250,000 for adding an Accessory Dwelling Unit (ADUs) built on their properties.

An ADU, up to 900 square feet, provides a homeowner with a free-standing or attached unit for aging parents, other relatives, or as full- or part-time rental units. ADUs are viewed by Plymouth and many other communities as a means to help lessen the shortage in housing without overly taxing a town’s utilities and road maintenance, and obviate land requirements for new construction.

The ADU loan program, offered by MassHousing, helps families “move from plans and permits to construction.”  The state maintains that the loan program, by providing financing, removes a major hurdle.  “It has been tricky securing loans for ADU construction, since you are creating two dwellings on a lot zoned for single-family use,” a state spokersperson explained.

Eligibility requirements include:

  • Meeting income limits up to 135% of Area Median Income, or AMI.  (That percentage translates to about $150,000 in household income for Plymouth residents, according to HUD data.)
  • Having approved construction designs/permits, and
  • Passing standard loan underwriting.

During the first six months of 2025, over 550 ADU had been approved in the Commonwealth.

In Plymouth, Spencer Dancause, town planner for Planning and Development, reports that the town has  granted 24 building permits for ADUs.  From those permits, 17 ADUs have been completed to date.

Plymouth has denied six zoning permits for ADU’s.  Why?  Either an ADU’s floor area exceeded the 900-square-foot maximum, or it did not meet required building setbacks for their lots.
There is not a specific lot size required for ADU’s themselves. Rather, they are allowed, by right, in single-family zoning districts as accessory to the primary dwelling, and subject to the same setbacks as the primary dwelling.  So, whether you have a conforming or nonconforming lot (undersized lot), as long as you can meet the building setback requirements and floor area requirements, zoning allows an ADU to be constructed.
Zoning also allows for existing accessory buildings to be repurposed into ADU’s, provided they meet floor area requirements and do not create or increase any nonconformities such as setbacks.

For more information on ADU zoning requirements and other ADU information contact: Steve Feldman at SteveF.kw.com or (617) 417-3125.