What Is an Accessory Dwelling Unit (ADU)?

An Accessory Dwelling Unit (ADU) is a small, independent home located on the same lot as a primary residence. It has its own kitchen, bathroom, sleeping area, and entrance, making it a complete living space distinct from the main house. ADUs can be created inside a home, attached to it, or built as a separate structure in the yard.

The Quick Definition:

• Where it sits:
  On the same lot as a single-family home.
• What it includes:
  Kitchen, bath, sleeping, and living areas, self-contained.
• How it connects:
  Separate entrance and privacy from the main home.
• Common names:
  Granny flat, in-law suite, carriage house, garage apartment, backyard cottage.

Why ADUs are on the rise?

ADUs give homeowners flexibility: room for multigenerational living, a private space for a caregiver, all while gently adding housing in existing neighborhoods. National resources emphasize that ADUs are self-contained homes that can help people age in place and broaden housing options without changing neighborhood character.

What an ADU Isn’t:

• Not a bonus room:
  The kitchen is the defining feature that separates an ADU from extra living space.
• Usually not on wheels:
  Tiny homes on wheels are a different category in most jurisdictions.

A Note for Massachusetts Readers:

Massachusetts recently made ADUs legal statewide (2025), with state documents defining an ADU as a self-contained housing unit with sleeping, cooking, and sanitary facilities on the same lot as a principal dwelling. Local rules still govern the details (size limits, where they can go, and how to permit them), but the statewide green light makes exploring an ADU more straightforward than before.

How ADUs Get Built (and Why Modular Matters):

ADUs can be site-built like any home, or delivered as modular units (constructed off-site in a controlled environment and installed on your property). Modular delivery can reduce delays, waste, and labor costs and make timelines more predictable, without compromising quality or design.

Why Homeowners Choose MassDwell for Their ADU:

If you’re considering an ADU in Massachusetts, MassDwell focuses specifically on high-quality modular ADUs, combining precision off-site construction with local regulatory know-how. Their approach prioritizes build quality (materials and workmanship) and a clean, efficient process from design through installation.

• Quality you can feel:
  MassDwell emphasizes architectural quality, durable materials, and factory precision, delivering homes that are built to last, a key differentiator in a market where not all ADUs are created equal.
• Faster, cleaner builds:
  The modular method drastically reduces delays and waste while keeping design standards high, helping you move from idea to move-in with fewer surprises.
• Clear models & specs:
  Choose from compact one-bedroom to larger two-bedroom layouts, each with a full kitchen and modern finishes, ready for living, renting, or multigenerational needs.
• Permitting support:
  MassDwell’s team handles zoning checks and permits, smoothing one of the most complex parts of an ADU project.

An ADU is a self-contained home that expands what’s possible on your property. With MassDwell’s quality-first, modular approach, you can unlock that space with better materials, tighter construction, and a smoother process, from concept to keys. Explore MassDwell’s ADU models and see what fits your lot and goals.