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Your Contractor for Accessory Dwelling Units in Southern NH and Northeastern MA

At Blackdog Design/Build/Remodel, we regularly design and build Accessory Dwelling Units (ADUs) for homeowners in communities such as Andover, MA, and Salem, NH. From early feasibility to final inspection, we guide you through the entire process with our end-to-end design/build services. 

What is an ADU?

An Accessory Dwelling Unit (ADU) is a self-contained living space located on the same property as your primary home. For many homeowners across Southern New Hampshire and Northeastern Massachusetts, an ADU is a smart way to expand your living space while staying in the neighborhood you love.

We often build ADUs in Essex, Middlesex, Rockingham, and Hillsborough Counties for a variety of reasons. Here are just a few of them.

ADUs are commonly used for:

  • In-law suites and multigenerational living

  • Guest houses or private home offices

  • Long-term or short-term rental units

  • Flexible living space that adapts as your needs change

Recent ADU Laws

We handle the paperwork, but sometimes it can help to read along. Here's the regulatory nitty-gritty if you want to add to your research. 

For New Hampshire homeowners:

For Massachusetts homeowners:

The Types of ADUs We Build for Homeowners on the North Shore (and Beyond) 

ADUs can take many forms, depending on your property and how you plan to use the space. We design and build attached ADUs, detached ADUs, and internal ADUs, including in-law suites, backyard cottages, garage apartments, and converted basement or attic units.

Attached ADUs

Attached ADUs are additions to your existing home, such as in-law suites or accessory apartments. These are especially popular with homeowners who want the new space to feel fully integrated with the main house.

Detached ADUs

Detached ADUs are stand-alone structures such as carriage houses, garage apartments, or backyard cottages. We frequently build detached ADUs for homeowners in spaces where backyard space allows for flexible design solutions.

Internal ADUs

Internal ADUs are created by converting existing space within your home, such as a finished basement or attic apartment. These projects are common in established neighborhoods, where homeowners want to maximize their existing footprint.

Our ADU Design/Build Services

At Blackdog Design/Build/Remodel, we believe your ADU should work beautifully for the way you live now and in the future. Our full-service design/build approach allows us to guide you through every step, creating a clear, organized, and predictable experience from start to finish.

Design and Planning

Every ADU project begins with thoughtful design and upfront planning. We evaluate your property, zoning, and site conditions, then work with you to define goals, establish a realistic investment range, and create a layout that fits your needs.

This early alignment helps ensure your ADU is designed with intention and built without surprises.

Project Management and Coordination

We manage your ADU project from start to finish. Our team handles permitting, engineering coordination, scheduling, and communication, so you are not managing multiple consultants or contractors.

With dedicated project managers and lead carpenters, your project stays organized and clearly communicated throughout construction.

Full-Scope ADU Construction

As a true design/build remodeler, we deliver your ADU under one roof. Our experienced carpenters and long-term trade partners execute the established plan with consistent craftsmanship and clear accountability.

Your completed ADU is backed by our industry-leading three-year warranty for long-term peace of mind.

Frequently Asked Questions About ADUs

Can You Build a Detached ADU?

Both Massachusetts and New Hampshire laws now allow detached ADUs on most single-family lots, with no special permit required.

How Large Can An ADU Be in New Hampshire and Massachusetts?

Size is a great question, and there is a different answer for each state.

In New Hampshire, ADUs range from 750 to 950 square feet. However, in Massachusetts, ADUs can be up to 900 sq ft or ½ the size of the primary home.

 

Can You Turn an ADU into a Short-Term Rental in New Hampshire and Massachusetts?

Owner-occupancy is not broadly required in either state, but some local municipalities or jurisdictions in both states may restrict short-term rentals. Always work with a team that can advise you on the most up-to-date information before you begin the process. 

How Long Does it Take to Build an ADU

Most ADUs take 6-9 months from design through completion, depending on permitting and site conditions. Working with a design/build firm means that you can move the process along more quickly than if you had to work with separate firms. 

Local ADU Services

So what do our ADU services look like across Southern New Hampshire and Northeastern Massachusetts?
Blackdog Design/Build/Remodel provides full-service Accessory Dwelling Unit (ADU) design and construction throughout Hillsborough and Rockingham Counties in New Hampshire, and Essex and Middlesex Counties in Massachusetts. With recent zoning changes expanding ADU opportunities across the region, homeowners are turning to our remodeling company for a clear, well-managed path through what can otherwise be a complex process.

Design and Planning

Every ADU project begins with a structured design and planning process. Our in-house designers evaluate existing conditions, zoning and code requirements, and site constraints while defining scope and realistic budget ranges. From layouts to detailed specifications, key decisions are made before construction begins—minimizing surprises later.

Project Management and Coordination

Blackdog Design/Build/Remodel manages your ADU project end-to-end. From permitting and regulatory coordination to scheduling, trade management, and consistent communication, our project managers and lead carpenters keep your project moving forward smoothly and efficiently.

Full-Scope Execution

As a true design/build firm, we deliver ADU projects under one roof. With dedicated lead carpenters and trusted trade partners executing a clearly defined plan, you can expect accountability, craftsmanship, and an ADU backed by our three-year warranty.

Your Resource for Building for ADUs in Southern NH and Northeastern MA

At Blackdog Design/Build/Remodel, we bring decades of experience to every ADU project (and all of our services), combining thoughtful design, clear planning, and disciplined construction under one roof. As a true design/build firm, we guide you through the entire process from early feasibility and design through permitting, construction, and warranty support, so nothing is left to chance. We serve homeowners throughout our Southern New Hampshire and Northeastern Massachusetts service area. Whether you are planning an in-law suite for aging parents, creating space for adult children returning home, or exploring rental income in a high-demand market like Andover, MA, our team helps you create a second living space that feels intentional, integrated, and beautifully built. Take a look at our cost guide and portfolio and start planning for your future. 

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Contact us today to schedule a consultation or get started. 

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Salem Showroom

Ready to take the next step towards making your dream home a reality? Visit one of the Blackdog showrooms or contact us today to get started.

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Salem, NH 7 Red Roof Lane, Unit 1
Salem, NH 03079 603-898-0868

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Nashua , NH 520 Amherst Street, Suite 2
Nashua, NH 03063 603-769-3344

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The information on this website is for informational purposes only; it is deemed accurate but not guaranteed. It does not constitute professional advice. All information is subject to change at any time without notice. Contact us for complete details.

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