With the lack of year-round housing continuing to be of concern throughout Cape Cod, paired with ever-increasing median home prices and high interest rates, homeowners are exploring the feasibility of building an Accessory Dwelling Unit (ADU) on their property. Barnstable County’s aging population is another consideration in building an ADU, as caregivers look to keep parents close to home while providing them with privacy.
In 2021, Governor Charlie Baker signed the Housing Choice Initiative, which provided funds and technical assistance for those looking to build ADUs for low-income or workforce housing. Another major aspect of the legislation was that it empowered municipalities to create bylaws within their own towns that would increase housing stock via accessory dwelling units. With the changes in legislation, something that has long been “frowned upon” is now being encouraged.
As of February 2025, the law was expanded, and now compels towns across the commonwealth to allow ADUs.
When it comes to building an ADU on Cape Cod, the specific regulations can vary significantly from town to town, as they do with any kind of residential or commercial building project.
All of the towns on the Mid, Lower and Outer Cape do permit ADUs. A cursory review of each town’s bylaws indicates the ADU must be reserved for year-round housing, with minimum lease terms and restrictions on using an ADU for short-term seasonal rentals. Most towns also require the owner live on the premises.
According to the information on the websites of several towns, an ADU on Cape Cod must be “clearly subordinate” to the primary home, meaning your new ADU needs to be substantially smaller.
Some towns require that an ADU be in a freestanding building, while others will allow the alteration of an existing structure – a basement, an over-the-garage bonus room, etc. – to create an ADU.
As an early adopter of new zoning bylaws, the Town of Brewster has seen great success in increasing its housing stock via ADUs, adding approximately 20 units per year, the maximum allowed, over the last 10-plus years.
In Brewster, ADUs can be no more than “…900 sqft of living space or 40% of the habitable dwelling, whichever is less.” An ADU cannot have more than two bedrooms. Unlike other towns, an ADU in Brewster can be built within an existing structure such as a basement or garage. When built into an existing structure, an exterior stairway must be provided for the ADU unless it is at ground level.
In the Town of Dennis, a minimum lot size of 15,000 sqft is required for an ADU and the maximum size of a unit is 800 sqft, about the size of two large hotel rooms. Owners must live on the property year-round but, in Dennis, they can opt to live in the smaller ADU and rent out the primary home. Dennis caps its allowable ADUs at nine new units per year.
To qualify for funding from the Commonwealth’s Housing Choice Initiative, homeowners must adhere to a rent structure that meets guidelines for either low-income or workforce housing, and other stipulations addressing issues such as occupancy and resale, etc. The initiative also provides technical assistance for those who wish to utilize it.
The first step in building an ADU on Cape Cod is determining its feasibility. There is no sense lining up funding and making plans if what you want simply is not possible.
Because the ADU regulations here do vary so much, engaging an experienced Cape Cod builder should be your very first step in the process. A Cape Cod custom builder builds homes throughout a region, rather than in just one town, and will have a working knowledge of the bylaws of several towns. If a builder is not able to answer a specific question, they will know which town official can provide that answer.
An experienced builder will also assist in guiding your plans for building an ADU through the town’s regulatory process, something an architect can adroitly handle, as well.
Whatever the reason – to generate income, provide much-needed housing stock, or care for a loved one – adding an accessible dwelling unit to your Cape Cod home can be a smart move. An ADU will likely also increase your home’s value exponentially.
Please contact us with any questions or to arrange a consultation.
