Straight answer, no runaround. Here’s what custom homes, ADUs, and additions typically run on the South Coast in 2026 — and, more useful, what actually moves the number up or down. These are planning ranges from real South Coast Building projects, not quotes. Use them to sanity-check your budget before you talk to anyone.
Typical project cost ranges — South Coast MA, 2026
| Project type | Typical planning range |
|---|---|
| Custom new home | $450,000 – $900,000+ (excludes land) |
| ADU / garage with apartment | $200,000 – $375,000 |
| Addition (build out) | $200,000 – $400,000 |
| Addition (build up / 2nd story) | $250,000 – $500,000+ |
| Major / whole-home renovation | $200,000 – $600,000+ |
Preliminary planning ranges based on past South Coast Building projects and current 2026 South Coast market data. Not a quote. Final pricing requires a site evaluation.
What drives the number
- Square footage & layout. Bigger and more complex — vaults, multiple rooflines — costs more per foot.
- Finish level. Builder-grade vs. mid vs. high-end can swing a project 30% or more. Kitchens and baths drive it most.
- Site work. Clearing, grading, ledge or blasting, and long driveways add up fast — before the foundation is even in.
- Septic & utilities. An existing system vs. a new septic vs. town sewer is a five-figure swing.
- Foundation & lot. Slope, wetlands setbacks, and soil conditions all move the number.
- For additions & renovations: the age and condition of existing electrical, plumbing, and HVAC — and whether demolition is needed.
- Energy code. MA Stretch code and a HERS rating are required, and we build them into our pricing — no surprise add-ons.
Building across the South Coast
We build in Westport, Dartmouth, Acushnet, Mattapoisett, Fairhaven, Freetown, Fall River, and New Bedford. Costs are similar town to town — what really moves your number is your lot’s site conditions (septic, ledge, slope, setbacks), not the town line.
Cost questions, answered
What does it cost to build a custom home on the South Coast of Massachusetts?
In 2026, most custom homes we build run $450,000–$900,000+ (excluding land), or roughly $250–$400 per square foot depending on size and finish. Site work and finish level move it the most.
How much does an ADU cost in Massachusetts?
Typically $200,000–$375,000, about $250–$375 per square foot. Detached units cost more than ones attached to or built over a garage. Most take four to five months.
What does a home addition cost in Dartmouth or Westport?
Building out, $200,000–$400,000. Building up (a second story), $250,000–$500,000+, because the existing house usually needs structural reinforcement.
What adds the most cost to a custom build?
Finish level (kitchens and baths), square footage, and site work — clearing, ledge, grading, and septic.
Do you give free estimates?
We give an honest planning range up front, then a firm contract price after a site evaluation. Start your project and we’ll get you a range for your specific lot and plans.
Why are these ranges so wide?
Because an honest builder won’t quote your house from a web form. These brackets get you in the right ballpark; a site visit tightens it.
Want a range tailored to your lot and plans?
Tell us about your project — your lot, your scope, your timeline — and we’ll come back with a real planning range and the next steps.