ADU construction

FlexUnit: a self-contained space, built the right way

Whether it's for an aging parent, a returning college grad, or rental income, an accessory dwelling unit (ADU) is one of the most valuable things you can add to your property. At Bay State Design & Construction, we've built our ADU service from the ground up — and even have it a name: FlexUnit™

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Modern wooden cabin with glass facade and string lights, outdoor table with chairs in gravel yard.
Logo of the National Association of Home Builders with a roof shape over the acronym NAHB.Black circle badge with NKBA logo and text reading Remodeling Specialist and NKBA Specialty Badge Program.Blue and white Better Business Bureau accredited business badge with torch symbol.Thumbtack logo above a blue hexagon with a yellow star and text Top Pro.Circle badge with text 30-HOUR OSHA CERTIFIED and a blue and gray OSHA logo.
42+
Years of Combined
Team Experience
763+
Completed
Projects
5★
Homeowner
rating Average

Our Approach

We built a whole process around getting ADUs right

An accessory dwelling unit (ADU) isn't a regular renovation. It's a second building on your existing property. That means zoning, code compliance, utility capacity, and structural feasibility all need to be worked out before a single wall goes up. Most ADU projects run into problems because that groundwork gets skipped. We don't skip it. Before we design anything, we assess what's actually possible on your property, legally, structurally, and financially. Once we know it's viable, we design it, draw the plans, pull the permits, and build it. Our promise to you: no guesswork, no surprises.

What's Possible
Basement conversions
Garage conversions
In-law suites
Guest houses
Rental units
Age-in-place additions
Attached ADUs
Detached ADUs

We're ADU specialists. And as such, we felt our ADU service deserved a name that reflects our expertise and the possibilities of what you can build. All of our FlexUnit ADU projects are properly permitted and designed around how you actually need (and want!) to use the space.

BSDC Logo badgeInterior view of a wooden frame house under construction with exposed studs and beams.

REASONS TO BUILD AN ADU

Why are homeowners building ADUs?

  • An aging parent needs to be close but wants their own space
  • A college grad is back home and a real separation makes sense for everyone
  • You want rental income without buying a second property
  • You want to increase your home's value and long-term ROI
  • You have unused space — a basement, a garage — that could be working harder
  • You want flexibility for however your household changes down the road
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What we can build

What could your ADU look lke?

Every lot is different. Every family's needs are different. Here's a look at what's possible — then let's figure out what makes sense for yours.

Evening view of a well-lit backyard patio with outdoor table, chairs, and attached guest house.
Attached ADU
Extra space that feels like part of the home, not an afterthought. Imagine a private entrance, its own living area, and all the function of a separate unit without leaving your property.
Gray two-story detached garage with white trim, black shutters, outdoor stairs, and driveway.
Detached ADU
You could have a fully independent structure in your very own backyard. Guest house, rental unit, studio, in-law suite...whatever you need it to be, we build it from the ground up.
Wooden framework of a building under construction against a bright blue sky with clouds.
Custom ADU
Have the space, but unsure what to do with it? We've transformed attics, basements, and garages into fully finished, livable units.

Our Portfolio

Snapshots of recent projects

Modern kitchen with white cabinets, stainless steel appliances, hardwood floor, and a large island with stools.Wooden frame construction of a house extension with green floor panels and ladder leaning inside.New kitchen under construction with white cabinets, open shelves, island base, and wood floors.Concrete foundation pit next to a house under construction with a folded ladder nearby.Modern kitchen with white cabinets, stainless steel appliances, a central island, and three gray bar stools.House under construction with green ZIP System sheathing panels and a red ladder leaning on the side.

REviews

Hear from happy homeowners

Great guys and easy to work with! I couldn't be happier with my beautiful new kitchen!

Steven M.

The best! Gave a super reasonable estimate and walked me through all the steps and timeline , finally have my (dream) kitchen.

Theresa C.

I highly recommend Bay State Design & Construction to anyone looking for reliable, skilled, and professional construction services.

Peter S.

These guys are amazing! Helped me build a two story addition with a master suite and I couldn't be more thrilled with the product.

Alyssa F.

The guys from Bay State design were prompt well priced and kept my project moving without missing a step. Great work guys!

Joshua H.

I hired these guys to build an attached garage at my house. Throughout the entire process they went above and beyond all expectations and their pricing was super fair.

Vlad A.

This team is very professional, communicative and great to work with. Gio provided comprehensive building plans for me within a short timeframe, as promised.

Katie S.

How it Works

Typical kitchen remodel process

1

Initial consultation

We start with a conversation about your goals, your property, and your budget expectations. If it looks like a good fit, we schedule an on-site visit to walk the property together.

2

On-site evaluation

We assess layout potential, ceiling height, structure, access, zoning considerations, and utility capacity. By the end of this visit we'll tell you honestly whether moving forward makes sense.

3

Feasibility & budget roadmap

The most important step. Before any design work starts, we dig into zoning, code requirements, utility needs, energy compliance, and what your budget will actually get you. You leave with a clear roadmap and no surprises. This is a paid pre-construction phase at $3,500 — credited in full if you move forward with us.

4

Concept design & scope alignment

With feasibility confirmed, we refine the layout and unit configuration, align scope with your budget and goals, and prepare for formal design and permitting.

5

Design development & permit documentation

We coordinate architectural drawings, structural requirements, and all supporting documentation prepared specifically for your town's requirements.

6

Permit application & construction

We handle submission, inspector coordination, and any required revisions. Because feasibility was completed upfront, this phase moves faster and with far fewer surprises. Once permits are issued, construction begins.

Person holding clipboard with house floor plan in a modern white kitchen.
Contract on clipboard with pen, blueprints, kitchen photos, and flooring samples on wood table.
Wooden framing structure of a house under construction with sunlight casting shadows inside.
Person using a ruler and pen to draw on architectural blueprints on a wooden table.
Stacks of wooden planks and bricks stored inside a sunlit warehouse or workshop.
Wooden framing structure of a house under construction with sunlight casting shadows inside.
Person holding clipboard with house floor plan in a modern white kitchen.
1

Initial consultation

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We start with a conversation about your goals, your property, and your budget expectations. If it looks like a good fit, we schedule an on-site visit to walk the property together.

Contract on clipboard with pen, blueprints, kitchen photos, and flooring samples on wood table.
2

On-site evaluation

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse varius enim in eros elementum tristique. Duis cursus, mi quis viverra ornare, eros dolor interdum nulla, ut commodo diam libero vitae erat. Aenean faucibus nibh et justo cursus id rutrum lorem imperdiet. Nunc ut sem vitae risus tristique posuere.

We assess layout potential, ceiling height, structure, access, zoning considerations, and utility capacity. By the end of this visit we'll tell you honestly whether moving forward makes sense.

Wooden framing structure of a house under construction with sunlight casting shadows inside.
3

Feasibility & budget roadmap

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse varius enim in eros elementum tristique. Duis cursus, mi quis viverra ornare, eros dolor interdum nulla, ut commodo diam libero vitae erat. Aenean faucibus nibh et justo cursus id rutrum lorem imperdiet. Nunc ut sem vitae risus tristique posuere.

The most important step. Before any design work starts, we dig into zoning, code requirements, utility needs, energy compliance, and what your budget will actually get you. You leave with a clear roadmap and no surprises. This is a paid pre-construction phase at $3,500 — credited in full if you move forward with us.

Person using a ruler and pen to draw on architectural blueprints on a wooden table.
4

Concept design & scope alignment

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse varius enim in eros elementum tristique. Duis cursus, mi quis viverra ornare, eros dolor interdum nulla, ut commodo diam libero vitae erat. Aenean faucibus nibh et justo cursus id rutrum lorem imperdiet. Nunc ut sem vitae risus tristique posuere.

With feasibility confirmed, we refine the layout and unit configuration, align scope with your budget and goals, and prepare for formal design and permitting.

Stacks of wooden planks and bricks stored inside a sunlit warehouse or workshop.
5

Design development & permit documentation

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse varius enim in eros elementum tristique. Duis cursus, mi quis viverra ornare, eros dolor interdum nulla, ut commodo diam libero vitae erat. Aenean faucibus nibh et justo cursus id rutrum lorem imperdiet. Nunc ut sem vitae risus tristique posuere.

We coordinate architectural drawings, structural requirements, and all supporting documentation prepared specifically for your town's requirements.

Wooden framing structure of a house under construction with sunlight casting shadows inside.
6

Permit application & construction

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse varius enim in eros elementum tristique. Duis cursus, mi quis viverra ornare, eros dolor interdum nulla, ut commodo diam libero vitae erat. Aenean faucibus nibh et justo cursus id rutrum lorem imperdiet. Nunc ut sem vitae risus tristique posuere.

We handle submission, inspector coordination, and any required revisions. Because feasibility was completed upfront, this phase moves faster and with far fewer surprises. Once permits are issued, construction begins.

Bay State Design & Construction

Why homeowners choose BSDC

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One point of contact, start to finish

No chasing down architects, contractors, or permit offices. You have one team and one person to call, from first sketch to final walkthrough.

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We design around your budget

Many firms design the dream, then hand you a bill that doesn't match it. We start with your number and build the plan around it — no sticker shock.

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Your vision survives the build

A lot gets lost when the design firm hands off to the contractor. We can draw the plans and build to them. AKA: what you approved is what gets built.

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Your timeline is ours to protect

When design and construction live under one roof, no one else's schedule can slow yours down. We control the process so you're not waiting on a separate third party to move forward.

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You focus on the fun part

Finishes, fixtures, how it all comes together — that's your job. Permits, inspections, scheduling, and the heavy lift? That's ours.

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75% of our work comes from referrals

We don't take that lightly. It means our clients trust us enough to send their family and neighbors our way. And we intend to keep earning that.

Frequently Asked Questions

ADU construction FAQs

An accessory dwelling unit is a self-contained living space on your existing property — its own entrance, kitchen, bathroom, and sleeping area. It can be attached to your home, built within it, or stand alone on the lot.

That's exactly what our feasibility phase is designed to answer. Zoning, lot size, setbacks, and utility capacity all factor in. Every town in Massachusetts has different requirements and we work through them before any design or construction begins.

Basement conversions, garage conversions, attached additions, and detached guest houses. The right type depends on your property, your goals, and what your town's zoning allows.

From the day we break ground, usually around 4-6 months. ADU projects vary due to the permitting and feasibility work involved. Once permits are issued and construction begins, timelines vary based on scope and type. We give you a realistic picture during the feasibility phase.

In most cases yes, though local zoning and owner-occupancy rules vary by town. We research your specific municipality during the feasibility phase and advise you accordingly.

It depends heavily on the type of ADU, the condition of the existing space, and what utility upgrades are required. Our feasibility phase produces a realistic budget range before you commit to anything — that's the point of doing it first.

Every project comes with a 1-year workmanship warranty. If something isn't right with our work, we come back and make it right.

Ready to explore what's possible?

An ADU adds value, flexibility, and possibility to your property. Let's find out what's feasible.

Free Estimate