Accessory Dwelling Units (ADUs) in Massachusetts & New Hampshire

Blackdog Design/Build/Remodel helps homeowners design and build beautiful, functional accessory dwelling units (ADUs) that add space, flexibility, and long-term value.

Whether you’re planning for aging parents, grown kids returning home, or simply need more breathing room, Blackdog helps you create a second living space that feels fully integrated, intentional, and beautifully built.

Serving homeowners throughout Rockingham & Hillsborough Counties in New Hampshire, and Essex & Middlesex Counties in Massachusetts.

What Is an Accessory Dwelling Unit (ADU)?

An Accessory Dwelling Unit (ADU) is a self-contained home located on the same property as your main house. Think of it as a smart way to expand your space without uprooting your life.

Some homeowners build ADUs to give family members independence while staying close, like an in-law suite or accessory apartment. Others create flexible spaces for guests, remote work, or long-term rental income. Whatever your reason, an ADU allows your property to grow and adapt as your life does.

ADUs can take several forms:

• Attached ADU: Additions to your existing primary home. Examples include accessory apartments, in-law suite additions, and primary bedroom suite additions.
• Detached ADU: A standalone separate structure in your yard, often above a garage or as a separate cottage. Examples include backyard cottages, carriage houses, guest houses,
• Internal ADU: Converted space within your existing home, such as a finished basement apartment or finished attic apartment.

Why New England Homeowners Love ADUs

• Creates independent living space for family, guests, or caregivers
• Generates reliable rental income or short-term housing flexibility
• Supports aging in place and multigenerational living
• Increases property value and utility without requiring a move

The New ADU Laws: More Possibility, Less Red Tape

In both Massachusetts and New Hampshire, new statewide laws have made it dramatically easier for homeowners to add an ADU in their jurisdictions. That means simpler permitting, less waiting, and fewer local restrictions.

In New Hampshire (HB 577, Effective July 1, 2025)

You can now build one attached or detached ADU by right on any lot zoned for a single-family home.

• Detached ADUs are now fully legal statewide
• No special zoning or conditional use permits needed
• Municipalities can’t impose stricter setbacks or parking rules than for single-family homes
• ADUs must be at least 750 sq ft (and up to 950 sq ft, or more if your town allows)

For NH homeowners, this means freedom – to design your property the way you actually live in it!

In Massachusetts (Affordable Homes Act, Effective February 2, 2025)

Massachusetts now guarantees that every homeowner in a single-family zone can build one ADU by right.

• No special permits or owner-occupancy rules
• ADUs up to 900 sq ft or half the size of your main home
• No extra parking required near transit
• Local bylaws can’t override state law

In short: building an ADU is no longer an uphill battle, it’s a smart, legal, and achievable way to make your home work harder for you!

Where We Build ADUs

Blackdog Design/Build/Remodel serves homeowners across Southern New Hampshire and Northeastern Massachusetts. We offer award-winning residential remodeling and renovation services, in addition to attached and detached ADU additions.

In New Hampshire:

• Rockingham County: Salem, Windham, Londonderry, Exeter, Hampton, Kingston, and surrounding communities
• Hillsborough County: Nashua, Amherst, Merrimack, Milford, Bedford, Hudson, Hollis and surrounding communities

 In Massachusetts:

• Essex County: Andover, North Andover, Peabody, Beverly, Methuen, Boxford, Newbury, Newburyport and the North Shore of Massachusetts
• Middlesex County: Reading, Melrose, Lexington, Concord, Chelmsford, Groton, North Reading, Wilmington, Winchester and surrounding communities

We know each municipality’s process and can help you navigate zoning, permits, and local review with confidence.

Our ADU Design & Build Process

Building an ADU can feel daunting, but with the right general contractor, it doesn’t have to be. Blackdog’s full-service approach handles every step, from design to final inspection, so you can focus on what really matters: how this new space will improve your life.

1. Feasibility & Site Assessment: We review your property layout, utilities, and zoning to confirm ADU eligibility.
2. Custom Design & Budget Planning: You’ll work with our award-winning design team to create a layout that fits your goals and budget.
3. Permitting & Engineering: We handle the paperwork and coordinate with your municipality for a smooth approval process.
4. Construction & Project Management: Our experienced craftspeople bring your ADU to life with clear timelines and communication.
5. Final Inspection & Move-In: We ensure every detail meets our quality standards, and yours.

Why Homeowners Trust Blackdog for ADUs

We’ve been designing and building thoughtful home solutions for more than 35 years, long before “ADU” was a buzzword.

Our team understands that this isn’t just about construction or remodeling, it’s about making your home work for your family’s next stage.

When you work with Blackdog, you get:

• Local expertise in NH & MA zoning and permitting
• Full-service support from the design process through building your project (and peace of mind with an unbeatable 3-year warranty!)
• Beautiful, practical design that enhances your property’s value and flow
• Transparent communication and clear timelines
• A trusted partner with decades of experience in your community

We don’t just build ADUs, we build peace of mind for homeowners who want to stay right where they are.