Accessory homes, also known as accessory dwelling units (ADUs), have become an increasingly popular solution for homeowners in Massachusetts looking to maximize their property’s potential. These secondary housing units create new opportunities to address the state’s growing housing needs by providing additional living spaces, generating rental income, and accommodating family members, all while tackling some of the pressing challenges of Massachusetts’ housing crisis. In this article, we will explore everything you need to know about accessory homes in Massachusetts, including their physical forms, state-specific regulations, financing options, and social benefits.

What is an Accessory Home in Massachusetts?

An accessory home, or accessory dwelling unit, is a secondary dwelling unit located on the same lot as a primary residence. In Massachusetts, ADUs are defined under recent legislation that allows property owners to build units up to 900 square feet by right in single-family zoning districts without requiring special or discretionary approval from local zoning boards. These units are designed to be self-contained living spaces, often including a kitchen, bathroom, and sleeping area.

Accessory homes come in various physical forms, such as basement apartments with a separate door or back door for private access, backyard cottages accessed directly from the yard, carriage houses, laneway houses, garage conversions, ADUs built above or attached to a garage, or tiny homes. For comparison, a tiny house on wheels offers mobility and a downsized lifestyle, but differs from a permanent ADU. The key characteristic is that they are detached or attached structures that provide additional living space without subdividing the property.

Accessory homes are sometimes referred to by other names like granny flats, in-law suites, or mini apartments, depending on their design and intended use. For example, a basement apartment may be an existing ADU within the main house’s foundation, accessed through a separate door, while a detached structure like a carriage house, a garage apartment, or a backyard cottage is built separately from the primary residence.

Benefits of Accessory Dwelling Units in Massachusetts

Accessory dwelling units offer numerous benefits for homeowners and communities across Massachusetts. One of the most attractive advantages is the potential for rental income. By creating a permitted ADU on their property, homeowners can rent out the unit to tenants, helping to offset mortgage payments or save money on living expenses. This additional income stream can be particularly valuable for retirees or those looking to refinance their home.

Beyond financial gains, accessory homes provide more options for housing within existing neighborhoods across the state. They can accommodate adult children who need their own space but want to remain close to family, support multigenerational households, or offer affordable housing alternatives in high-demand areas like Boston, Cambridge, and Worcester. These units help increase housing density without requiring new infrastructure or expanding urban sprawl, making them a sustainable solution to Massachusetts’ housing crisis.

The recent Affordable Homes Act passed in 2024 highlights the state’s commitment to jumpstarting housing production and easing zoning restrictions for ADUs. The law allows property owners to build ADUs up to 900 square feet by right in single-family zoning districts, removing barriers that previously limited ADU development. Social benefits also arise from ADUs by fostering community connections and providing flexible living arrangements for family members. In-law suites or granny flats allow aging parents to live independently while staying close to their loved ones, reflecting changing family dynamics and preferences.

Physical Forms and Types of Accessory Homes in Massachusetts

Accessory homes in Massachusetts come in a variety of physical forms, each suited to different property types and local zoning regulations. Common types include:

• Basement Apartments: These living spaces created within the basement of a single-family home utilize existing space and often require modifications to meet Massachusetts building code requirements, such as adding egress windows for natural light and separate entrances.
• Backyard Cottages and Granny Flats: Detached structures built in the backyard, these units are standalone homes that provide privacy and independence from the main home.
• Carriage Houses and Laneway Houses: Typically found in urban areas, carriage houses are built above garages or in alleys (laneways), maximizing underutilized spaces.
• Tiny Homes and Mini Houses: Small, efficient living spaces that can serve as ADUs, offering affordable and compact housing options.

Each type of accessory home must comply with Massachusetts’ ADU regulations, local zoning bylaws, and state building codes, which dictate aspects like size limits, setbacks, parking requirements, and permitted uses.

At VIACAD, LLC., we understand that the foundation of a successful accessory home project starts with well-crafted design plans. Many homeowners underestimate the importance of having detailed blueprints before contacting contractors. Often, the process is reversed; homeowners approach contractors first, who then reach out to building designers like us. By engaging VIACAD, LLC. early to develop your residential plans, you gain control over the bidding process, allowing you to seek and compare bids from multiple contractors based on the same clear, precise plans. This approach helps protect your investment by reducing surprises, change orders, and delays during construction.