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The ADU Design-Build Process: What Homeowners Should Expect

Design-build means one team is responsible for your ADU from the first feasibility conversation through the final walkthrough, design, permitting coordination, and construction under a single contract, with a single point of contact. The alternative is hiring an architect, taking the drawings out to bid, and then managing the handoffs between designer, builder, and your town yourself. R&D Building Solutions runs ADU projects as design-build so decisions happen in the right order: what your lot can support before design, what the design costs before permits, what the schedule looks like before you commit to construction. This page walks through each stage, what you decide, what you receive, and what we handle, so you know what you're agreeing to before you agree to it.

Request a Project ConsultationCould an ADU work for your property?

Sound familiar?

The situations this service solves

You paid for drawings once and don't want to pay twice

The classic fragmented-project failure: an architect designs the ADU, the bids come back far beyond what you had planned, and the drawings go back for a paid redesign. In design-build, pricing develops alongside the design, so you find out what a decision costs while you can still change it.

You don't know whether to call a designer, a builder, or the town first

ADU projects have a real order of operations, and starting in the wrong place wastes money, designing before you know what the lot supports, or asking the town about a plan that doesn't exist yet. Design-build gives you one starting point: a feasibility conversation that sets the sequence for everything after it.

You don't want to be the go-between

When the designer and the builder work for you separately, you carry messages between them, and when a detail on paper doesn't work on site, each can point at the other. With one team under one contract, a constructability problem is our problem to resolve, not yours to referee.

You can't tell whether a stalled project is normal or a warning sign

Every stage of our process ends with something you can hold in your hands, a feasibility summary, a priced design, a permit submission, a written construction plan. If you don't have the deliverable, the stage isn't done, and you'll know exactly what's holding it and who is moving it.

Project types

The kinds of projects we take on

Design-build with one team

One contract covers feasibility, design, permitting coordination, and construction, with one party accountable for the result. The honest tradeoff: you commit to your builder before the design is finished, so vet the team's process and references carefully. This page shows you what our version of that process looks like.

Architect first, then competitive bids

You get an independent designer and the ability to compare builder prices, real advantages. Where it commonly stalls: bids come back over the design's assumptions, no single party owns whether the drawings are buildable on your specific lot, and you manage every handoff yourself. It can work well for homeowners with the time and experience to run it.

Acting as your own general contractor

You hire and schedule each trade yourself and keep the coordinator's margin. Be honest with yourself about the workload: sequencing trades, chasing inspections with your town, and owning every gap between subcontractors is a serious ongoing commitment, and mistakes in the order of work are expensive to unwind.

Adapting stock or catalog ADU plans

Pre-drawn plans can shorten the design conversation and are worth considering. The catch in our region: older lots, septic systems, setbacks, and existing structures rarely match a plan drawn for a generic site, so someone local still has to adapt the design and confirm it works, which is where the real effort was all along.

Think it through

Planning considerations

Name one decision-maker for your household

Design-build moves through decision points in sequence, and each one closes the door on cheap changes to the one before it. Agree at home on who gives the final answer, projects drift when every selection reopens a settled question.

Set your walk-away number before design starts

Not a budget you hope for, the figure beyond which the project stops making sense for you. The feasibility stage exists to test your property against that number honestly, before you've spent real money on design.

Know what you're buying at each stage

Before you pay for a stage, you should be able to say what document or decision you'll have at the end of it. Ask us, or any builder you talk to, that question directly. Vague answers at the proposal stage become vague projects.

Gather your property paperwork early

A plot plan, septic records if you have them, and anything you know about past additions or work on the house. On older properties around here, what's on paper and what's in the ground don't always match, and finding that out during feasibility is far better than finding out during excavation.

Decide how you'll live alongside the work

An attached or basement ADU means crews inside or against your home; a detached unit means equipment crossing your yard. Think through driveway access, pets, work-from-home noise, and which door the crew uses, these become part of the written construction plan if you raise them early.

How we work

Our process for this work

  1. First conversation

    You tell us what the ADU needs to do, house a parent, bring an adult child home, create rental flexibility, and we tell you plainly whether your situation fits a design-build approach and what we'd look at first. No drawings, no commitment.

  2. Feasibility and site review

    We look at what your lot and structures can actually support: access, septic and utilities, the condition of any space you'd convert, and what your town generally requires for an ADU. You receive a clear picture of your realistic options before any design money is spent, including, sometimes, the news that the version you wanted doesn't make sense.

  3. Design developed with pricing attached

    The design and its construction cost move together. Each time the drawings develop, the price develops with them, so tradeoffs, another bathroom, a bigger kitchen, a different roofline, are decisions you make with the cost in front of you, not surprises after bidding.

  4. Permit submission and town coordination

    We prepare the documents your town's building department requires, submit them, and respond to questions or requested revisions. You review and sign what needs your signature. Requirements vary by town, and the review timeline belongs to the town, not to us, but you'll always know what's pending and what we're doing about it.

  5. Pre-construction planning

    Before work starts you receive a written plan: the schedule as we honestly see it, site logistics, what happens in what order, and the dates by which your remaining selections are needed. This is where clear expectations get set, in writing, before the first truck arrives.

  6. Construction with communication on a rhythm

    Work proceeds against the plan, inspections happen at the points your town requires, and you hear from us on a regular schedule, not only when something goes wrong. When a decision needs you, it comes with context and options, not just a question.

  7. Final walkthrough and closeout

    We walk the finished unit with you, list anything that isn't right, and fix it. You receive your closeout documents, and the project ends when the work meets the standard, because quality is the requirement, not an upgrade option.

Honest expectations

What shapes schedule and cost

No invented numbers, these are the real levers, so you can reason about your own project before we ever talk.

What can affect the schedule

  • Your town's permit review queue and inspection scheduling, the part of the calendar no builder controls
  • How early you finalize selections; late changes to fixtures, windows, or layout ripple through everything ordered after them
  • Whether septic, well, or utility-connection work is involved, which adds other parties' schedules to yours
  • The season, frozen ground, snow, and exterior work windows are real constraints in New England
  • What opens up when we open up: conversions in older homes sometimes reveal framing, moisture, or wiring conditions that must be corrected first
  • Lead times on ordered items, which vary by product and supplier and are locked in when selections are finalized

What can affect cost

  • The type of ADU, converting existing space, converting a garage, adding on, or building detached are very different scopes
  • Site conditions: ledge, grading, drainage, and how easily equipment can reach the work area
  • Septic capacity on unsewered lots, whether the existing system can support another dwelling or needs work
  • Bringing utilities to the unit: water, wastewater, electrical service, and heat
  • The condition of the existing structure in a conversion, older foundations, framing, and moisture history all matter
  • Kitchens and bathrooms, which concentrate most of the cost in any small dwelling; count and finish level drive more than square footage does
  • When changes happen, the same change costs more after permits than during design, and more during construction than either
  • Requirements your town applies to a second dwelling, which vary from town to town

Permits & inspections

An ADU needs a building permit, and the work is inspected at stages your town's building department sets. As your design-build team, we prepare the submission, file it, answer the department's questions, handle requested revisions, and schedule inspections as construction reaches them, that is what coordination with your town actually means. What we can't do is promise an outcome: requirements vary by town, review takes the time it takes, and the decision belongs to your local officials. What you can expect from us is that the application reflects your town's stated requirements, that you always know the current status, and that nothing sits because no one was watching it.

Why R&D

How we do this differently

The price grows up with the drawings

You will never be handed a finished design and then discover what it costs. Every design decision is made with its cost visible, which is the single biggest protection design-build offers your budget.

One name on the whole project

If a detail that worked on paper doesn't work in the field, there is no designer-versus-builder standoff, the team that drew it is the team building it, and resolving it is our job. You should never have to referee your own project.

Stage deliverables you can point to

Feasibility summary, priced design, permit submission, written construction plan, closeout documents. At any moment you can name the stage you're in and hold the paper that ended the last one. That is what an organized, transparent process means in practice.

Communication doesn't end at the signature

The industry's quiet failure is the builder who is responsive right up until the contract is signed. Our commitment runs the other way: updates on a set rhythm during construction, real answers when something shifts, and a phone that gets answered.

Questions homeowners ask

What does design-build actually mean?

One company is responsible for both designing your ADU and building it, under one contract, with one point of contact. The alternative, hiring a designer, then bidding the drawings out to builders, separates the person who draws the project from the person who has to make it work, and leaves you managing the gap between them. Design-build closes that gap.

Is design-build cheaper than bidding the project out?

Not automatically, and anyone who promises that is guessing. What design-build genuinely changes is when you learn what things cost: during design, while decisions are still cheap to change, instead of after, when the only fix is a redesign. You give up comparing bids; you gain a price that was built alongside the plan. For many homeowners that trade is worth it, but it is a trade, and you should make it knowingly.

I already have drawings from an architect. Can you build from them?

Often, yes, but we'll review them for constructability and cost on your specific lot before we price anything, and we'll tell you honestly if we find problems. Some of what you'd have gained from design-build has already been spent by that point, but the construction side of our process works the same way.

How long does the whole process take?

We won't put a number here, because any number that covers both a basement conversion and a new detached unit, across every town's review process, would be fiction. What we will do is give you our honest expected schedule for your specific project before you commit to construction, and tell you promptly when anything moves it.

What happens if the town asks for changes to the design?

Revisions during permit review are a normal part of ADU projects, not a crisis. Because the design team and the construction team are the same people, we make the revision, confirm what it means for cost and schedule, and resubmit, you're informed at each step rather than coordinating between an architect and a builder who are pointing at each other.

When do I actually sign a construction contract?

After the design is settled and priced, and the permitting picture is clear, not before. Earlier stages have their own smaller agreements, so you are never paying for work that hasn't been defined. You should always know exactly what you've committed to and what you haven't.

We run this design-build process for homeowners across Massachusetts and New Hampshire. Part of the work is local by nature: every town's building department has its own expectations for ADU submissions, and learning yours is our job, not yours.

Start with the cheapest step

The process begins with a conversation, not a contract, you tell us what you want an ADU to do, and we give you a straight first read on whether your property can do it. Call or send a note. We answer the phone, and if the honest answer is that this project isn't right for you, that is the answer you'll get.

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How Massachusetts ADU rules work in plain English: what the state law allows by right, what your town still controls, and how to plan an accessory dwelling unit project step by step.

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A printable checklist of the property, household, and town questions that decide whether an ADU is realistic, what to observe, measure, and gather before design money gets spent.

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ADU Cost Factors

The real cost drivers behind an ADU project, unit type, site work, septic, kitchens and baths, systems, and finishes, explained honestly so you can budget with your eyes open.

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