What is an Accessory Dwelling Unit (ADU)?

An Accessory Dwelling Unit (ADU) is a secondary residential unit located on the same property as a primary home. ADUs can take the form of detached backyard cottages, garage conversions, basement apartments, or attached additions. In Massachusetts, evolving zoning laws have made ADUs one of the most powerful tools available to homeowners.

How much does it cost to build an ADU in Massachusetts?

ADU costs in Massachusetts vary based on type and size. Detached ADUs (new construction) typically range from $325,000–$375,000 for ~550 sq ft, $450,000–$550,000 for ~750 sq ft, and $550,000–$750,000+ for ~900 sq ft. Attached or interior conversion ADUs generally range from $150,000–$350,000. Final costs depend on site conditions, utility requirements, and finish level.

Do I need a permit to build an ADU in Massachusetts?

Yes. ADUs in Massachusetts require local zoning approvals and building permits. Requirements vary by municipality and depend on the ADU type, lot size, setbacks, and utility capacity. R.H. Blanchard manages the full permitting process, including local zoning approvals, building permits, and coordination with municipalities and inspectors.

What types of ADUs can I build in Massachusetts?

The most common ADU types in Massachusetts include detached backyard cottages, garage conversions, basement apartments, and attached additions. The best type for your property depends on your lot size, zoning, existing structure, and goals. We evaluate your property and help you determine what is feasible and financially sensible.

How long does it take to build an ADU?

ADU timelines depend on type and complexity. Traditional site-built ADUs typically take 9–18 months from feasibility through certificate of occupancy, including design, permitting, and construction. Modular ADUs can have shorter construction timelines due to factory fabrication, though permitting timelines remain similar. We provide realistic schedules during the feasibility phase.

What is the difference between a traditional and modular ADU?

A traditional ADU is built on-site, offering full customization, seamless integration with your existing home, and flexibility in size, layout, and materials. A modular ADU is factory-built and set on your site, offering faster construction timelines, controlled costs, and consistent quality control. R.H. Blanchard builds both types and helps you choose the best option for your property and budget.

Can I rent out my ADU in Massachusetts?

Yes. Generating rental income is one of the most common reasons homeowners build ADUs. Massachusetts ADU regulations vary by municipality, and state legislation has been expanding ADU rights statewide. We help clients evaluate rental income potential and ensure full compliance with applicable regulations.

Does R.H. Blanchard handle ADU permitting and zoning approvals?

Yes. R.H. Blanchard manages the full permitting and approval process for ADU projects across Massachusetts, including local zoning approvals, building permits, coordination with municipalities and inspectors, and 780 CMR building code and energy code compliance. We handle the complexity so homeowners can focus on their goals.

Accessory Dwelling Units (ADUs) - R. H. Blanchard Contract & Design

Accessory Dwelling Units (ADUs) in Massachusetts

At R.H. Blanchard Contract & Design, we help Massachusetts homeowners unlock the full potential of their property through thoughtfully designed and expertly built Accessory Dwelling Units. Whether you’re creating space for family, generating rental income, or increasing long-term property value — we provide a complete, start-to-finish solution from feasibility and design through permitting and construction.

A Quick Primer

What Is an Accessory Dwelling Unit?

An ADU is a secondary residential unit located on the same property as a primary home. In Massachusetts, evolving zoning laws and housing initiatives have made ADUs one of the most powerful tools available to homeowners. We help you determine what’s possible on your property and what makes the most financial sense.

ADUs Can Take Several Forms

Detached ADU

Our ADU Process

A Streamlined Path From Concept to Certificate of Occupancy

Feasibility & Budget

We evaluate your property, zoning, utilities, and layout and set a realistic budget range.

Design & Fixed Pricing

We develop layouts, coordinate engineering and code compliance, then issue a fixed-price contract.

Permitting & Approvals

We handle local zoning approvals, building permits, and all coordination with municipalities.

Construction

Dedicated project management, clear communication, high-end craftsmanship, and a clean site.

Pick Your Path

Two Ways to Build Your ADU

Both routes deliver high-quality, code-compliant ADUs. The right choice depends on your priorities.

Stick-Built

Traditional ADU Construction

For homeowners who want full customization, we offer ground-up and renovation-based ADU construction.

Ideal For

Unique property layouts, historic homes, tight zoning, high-end finishes, or structural modifications.

Advantages

Fully customizable design, seamless integration with existing home, flexibility in size, layout, and materials.

Factory-Built

Modular & Prefabricated ADUs

We partner with leading manufacturers like KBS Builders to deliver high-quality modular ADUs. As your local GC, we manage site work, foundation, utility connections, modular set, finish integration, and final inspections through occupancy.

Ideal For

Faster project timelines, controlled construction costs, efficient repeatable designs.

Advantages

Reduced construction duration, factory-built quality control, less on-site disruption.

Why Choose Us

Why Work With R.H. Blanchard?

Massachusetts ADU Expertise

We understand local zoning, permitting, and building codes including 780 CMR and municipal-specific requirements that make ADU projects uniquely complex.

Design-Build Model

One contract, one unified team. No friction between designer and contractor. We manage the entire process, reducing risk and keeping your project on schedule and on budget.

Fixed-Price Contracts

We provide fixed-price construction budgets after the design phase so you know exactly what you’re building and what it costs before a shovel hits the ground.

Modular & Traditional Options

We build both traditional stick-built ADUs and partner with leading manufacturers like KBS Builders for modular/prefab, giving you flexibility on timeline and cost.

Real-World Experience

Top 1% of Massachusetts contractors (BuildZoom Score 175). 5-star reputation. Owner directly involved in every project. We bring accountability that larger firms can’t match.

2026 Pricing Guide

ADU Cost in Massachusetts

Understanding cost is critical when planning an ADU. Below are realistic pricing ranges based on current Massachusetts market conditions. Actual costs vary based on home and site conditions.

15+ Years building in MA

Detached ADU - New Construction

~550 sq ft

Compact backyard cottages.

$325k

to $375k

Detached ADU - New Construction

~750 sq ft

One-bedroom standalone unit.

$450k

to $550k

Detached ADU - New Construction

~900 sq ft

Two-bedroom or extended floor plan.

$550k

and up

Attached ADU - Within Existing Structure

Interior Conversion or Addition

Basement, garage, or attached addition.

$150k

to $350k

Pricing is influenced by scope, site conditions, utility requirements, and finish level. We provide fixed-price budgets after your feasibility and design phase.

Plan Before You Pour

What to Know Before You Build

ADU projects involve more than construction. They require strategic planning. We help clients navigate:

Zoning & Setbacks

Lot-specific zoning restrictions and setback requirements.

Owner Occupancy

Owner-occupancy requirements where applicable.

Parking Regulations

Local parking minimums for ADU additions.

Utility Capacity

Sewer, water, and electrical service availability.

Fire Protection

Sprinkler and alarm requirements per code.

Energy Compliance

Insulation standards and energy code requirements.

Our goal is to identify risks early and control costs before construction begins.

Service Area

ADU Builders Serving the North Shore & Greater Boston

Andover

Garage conversions, basement apartments, and attached additions. We navigate Andover’s zoning bylaws, utility upgrade requirements, and architectural integration.

North Andover

Detached and attached ADUs on larger residential lots.

Newburyport

Detached ADUs, outbuilding conversions, and high-end coastal or historic integrations. We focus on architectural character and septic/sewer constraints.

West Newbury & Newbury

Larger lots with strong potential for detached backyard cottages. We evaluate septic capacity and design for long-term property value.

Amesbury

Rental-income ADUs and multigenerational housing. ROI-focused planning and cost vs. value alignment.

Boston

Basement ADUs, rear additions, and compact urban layouts. We specialize in navigating strict Boston zoning, fire protection requirements, and utility limitations.

Also Serving

Bedford

Beverly

Burlington

Chelmsford

Dracut

Lowell

Malden

North Reading

Reading

Tewksbury

Wakefield

& Surrounding Communities

Ready to Build Your ADU?

Schedule a no-obligation consultation. We’ll evaluate your property, walk you through what’s possible, and show you a realistic budget range.