ADU Rules in Marion, MA

By , CEO and Master Builder, BuildX

Yes. You can build an ADU in Marion now, under Massachusetts state law. Marion is also drafting a local bylaw (Section 230-8.14) that would allow ADUs up to 1,200 sq ft. The friction is not whether ADUs are allowed. It is Buzzards Bay watershed protection, sewer or septic status, coastal flood zones, and confirming where the draft local bylaw stands.

Reviewed by Buz Artiano · September 20, 2026 State law applies now (760 CMR 71.00) Local bylaw Section 230-8.14 in progress Marion is BuildX home territory 19 sources reviewed

Call BuildX: (781) 627-7000

Marion ADUs are legal now, with a local bylaw in progress

State law applies today · Draft Section 230-8.14 pending adoption

Marion has not yet finalized a local ADU bylaw, but ADUs are already legal under Massachusetts state law. Under 760 CMR 71.00 (effective January 31, 2025) [760 CMR 71], protected-use ADUs of 900 sq ft or less are allowed by-right in zones that permit single-family dwellings, subject to the building code and septic capacity. Marion is separately drafting Section 230-8.14, which would allow ADUs up to 1,200 sq ft, with a Special Permit required for the 900 to 1,200 sq ft range [Section 230-8.14]. Confirm the current adopted status of Section 230-8.14 with the Building Department before you plan a project that depends on the larger size.

Legal now (state law) Marion is BuildX home territory Up to 1,200 sq ft proposed Local bylaw in progress

Can I build an ADU in Marion, MA?

Yes. ADUs of 900 sq ft or less are allowed by-right today under Massachusetts state law (760 CMR 71.00) in zones that permit single-family dwellings. Marion is drafting a local bylaw, Section 230-8.14, that would allow ADUs up to 1,200 sq ft, with a Special Permit for the 900 to 1,200 sq ft range. Confirm the adopted status with the Marion Building Department.

Show the draft bylaw, the state-law floor, and what is still being confirmed

Marion's Planning Board and Select Board held a joint meeting on October 7, 2024 and reached consensus on the shape of a new ADU bylaw [Sippican Week]. The town then published a draft of Section 230-8.14, dated January 21, 2025 [Section 230-8.14]. The draft sets out three things worth knowing:

  • Size: Up to 900 sq ft is by-right (the state-law floor). 900 to 1,200 sq ft requires a Special Permit. [Section 230-8.14]
  • Districts: Allowed as-of-right in Residence A through E, plus General Business and Marine Business. [Section 230-8.14]
  • Forms: Form A (within a one-family dwelling) and Form B (within an accessory building on the same lot). [Section 230-8.14]

The state-law floor is firm regardless of the draft. Under 760 CMR 71.00 [760 CMR 71], a protected-use ADU of 900 sq ft or less, on a lot in a zone that allows single-family dwellings, is by-right and not subject to a local owner-occupancy requirement. That protection applies today. The 900 to 1,200 sq ft range that Marion's draft proposes is NOT a protected-use ADU, so the town can attach local conditions (including a Special Permit and potentially owner-occupancy or short-term-rental conditions) to that larger range.

What is still being confirmed. The final adopted text of Section 230-8.14, its Attorney General approval status, and the treatment of short-term rentals are not yet verified. Marion officials discussed tying short-term-rental permission to owner-occupancy as a possible local condition, which their staff described as potentially workable subject to legal review [Sippican Week]. Whether that survives into the adopted bylaw is a Planning Department question. Confirm the current adopted status with the Marion Building Department at (508) 748-3516 before designing to the 1,200 sq ft figure.

For most Marion homeowners, the practical answer is straightforward: a protected-use ADU of 900 sq ft or less is buildable now under state law. The larger 1,200 sq ft option is a Marion-specific upside that depends on the final adopted bylaw and a Special Permit.

Garage conversion ADU

A garage conversion typically maps to Form B in Marion's draft Section 230-8.14: an ADU entirely within an accessory building on the same lot. If the garage is attached to the house, the project may instead fall under Form A (substantially within the one-family dwelling). Marion has not finalized the bylaw, so confirm how the Building Department classifies your specific configuration.

  • If the garage is detached: Likely Form B (entirely within an accessory building on the same lot) [Section 230-8.14]
  • If the garage is attached to the house: Likely Form A (substantially within the one-family dwelling)
  • Best for: Properties with a structurally sound existing garage; reuse of foundation, walls, and roof; faster than ground-up construction
  • Watch for: Foundation adequacy, insulation upgrades, separate-entrance and bathroom plumbing, sewer or septic capacity, and any Buzzards Bay watershed or flood-zone constraints on the parcel

Marion ADU Rules at a Glance

The six things most homeowners ask first. Tap "View all rule details" for the complete data set.

ADUs Allowed Yes State law now; local bylaw in progress
Max Size 900 sq ft by-right Up to 1,200 proposed (Special Permit)
Permit Path Building permit Special Permit for 900 to 1,200 sq ft
Special Permit Not for 900 sq ft or under Required for 900 to 1,200 sq ft
Short-Term Rental Being decided Owner-occupancy linkage explored
Biggest Cost Variable Septic and watershed $30,000 to $60,000 if septic upgrade needed
View all Marion rule details
  • ADUs allowed (state law): By-right, 900 sq ft or less, in zones permitting single-family dwellings [760 CMR 71]
  • Local bylaw status: Draft Section 230-8.14 (January 21, 2025). Confirm the current adopted status with the Marion Building Department. [Section 230-8.14]
  • Max size (draft): Up to 1,200 sq ft, with Special Permit for 900 to 1,200 sq ft [Section 230-8.14]
  • Districts (draft): Residence A, B, C, D, E, plus General Business and Marine Business [Section 230-8.14]
  • ADU forms (draft): Form A (within one-family dwelling), Form B (within accessory building) [Section 230-8.14]
  • Owner-occupancy: Preempted by 760 CMR 71.00 for protected-use ADUs (900 sq ft or less) [760 CMR 71]
  • Sewer status: Mixed. Substantial public sewer in Marion Village; outlying areas on septic
  • Sewer connection: Required for ADUs in sewered areas, subject to DPW capacity review [Section 230-8.14] [DPW]
  • Aquifer overlay: Aquifer and Zone II wellhead protection overlays apply [MassGIS]
  • Coastal flood zones: Sippican Harbor, Buzzards Bay coastline, Mattapoisett Harbor frontage [FEMA]
  • Watershed: Buzzards Bay watershed; Marion Town House hosts the BBAC mailing address [BBAC]
  • Dimensional standards: Per the Marion Zoning Bylaw. Confirm exact lot, setback, and height values with the Marion Planning Department.
  • Permitting: Online Permitting via the town website. Confirm the platform with the Building Department.
Why BuildX

Why BuildX Knows Marion ADUs

Marion is part of BuildX's South Shore home territory. We work Marion every month and know the Buzzards Bay watershed, sewer, flood-zone, and coastal-village constraints that drive your project.

Home Territory

Marion is BuildX home territory. We are your neighbors, not a regional contractor. We work the South Coast every month, so we know Marion's coastal parcels, sewer or septic status, flood-zone issues, and watershed questions firsthand.

See One in Person

Walk through a real, finished BuildX ADU before you sign anything. Private showings are available by appointment.

Day 1 Property Review

Before quoting, we check zoning, sewer or septic, FEMA flood zone, Buzzards Bay watershed, wetlands, and aquifer overlay status.

We Work Marion Every Month

Marion is part of BuildX's South Shore home territory. We work Marion every month designing ADUs for your neighbors. We bid Marion ADU projects regularly as part of our standard business operations. We don't have a Marion build on the board yet. Yours could be the first.

What we've built nearby: the Callinan ADU in Wareham, which borders Marion to the north and west, the Bradford ADU in Mattapoisett, just to the east, and the Desousas ADU in Acushnet, the next town over. And across the South Shore and South Coast, BuildX has an active pipeline of ADUs in two dozen towns.

Real families. Real builds. Real ADUs on the South Shore. See more BuildX ADU builds →

Not sure if your parcel is sewered, or in the Buzzards Bay watershed? Watershed, septic, and flood status drive Marion ADU cost more than zoning does. Ask BuildX to check before you start designing.
Request Property Review

What Can Complicate a Marion ADU?

Marion is a small, affluent coastal town on Buzzards Bay. Your parcel's water-quality, sewer, and flood overlays, not the bylaw, are usually what move project cost and timeline. The factors that come up most often:

Do I need septic approval for a Marion ADU? Septic

Likely affects you if: your parcel is outside Marion Village or any other sewered area and relies on a private septic system.

Yes if your parcel is on private septic. Marion has substantial public sewer in Marion Village (the central village), but outlying areas rely on private septic. Adding a bedroom adds wastewater design flow, so a Title 5 inspection and capacity check are typically required before an ADU permit is approved [Title 5].

Cost impact: $30,000 to $60,000 for a Title 5 capacity check plus possible system replacement when an older system cannot carry an additional ADU bedroom.

Coastal nitrogen consideration: Marion is not formally a Cape Cod town, but it shares nitrogen-sensitive coastal characteristics with Cape towns, which can drive stricter septic standards near the bay. Confirm with the Marion Board of Health [Board of Health] whether any nitrogen-sensitive area rules apply to your address [Title 5].

If your parcel is in a sewered area, the draft Section 230-8.14 requires connection to public sewer, subject to DPW review for capacity [Section 230-8.14] [DPW]. Confirm sewer availability by your specific address before design.

What flood-zone rules affect Marion ADUs? Coastal flood

Likely affects you if: your parcel is along Sippican Harbor, the Buzzards Bay coastline, Mattapoisett Harbor frontage, or any coastal or low-lying parcel mapped in a FEMA flood zone.

Marion has extensive Buzzards Bay coastal exposure. Significant FEMA flood zones run along Sippican Harbor, the Buzzards Bay coastline, and the Mattapoisett Harbor frontage on the eastern boundary [FEMA]. ADU projects on these parcels are different projects.

Cost premium: 15% to 25% on top of base ADU cost for elevation, breakaway walls, and engineer-stamped flood compliance.

Design requirements: FEMA-compliant elevation above base flood elevation, breakaway lower-level walls in V-zones, engineer-stamped structural design, flood-resistant materials, and utility elevation.

Coastal storm vulnerability is significant in Marion. Engineer-stamped flood compliance is non-negotiable on the permit side for coastal parcels.

How does Buzzards Bay watershed protection affect Marion ADUs?

Likely affects you if: your parcel is near the bay, a cove, or a tidal area, or relies on a septic system in a nitrogen-sensitive coastal area.

Buzzards Bay water quality is the dominant regional consideration in Marion. The Marion Town House serves as the mailing address for the Buzzards Bay Action Committee (BBAC), the regional water-quality coalition for the watershed [BBAC]. ADUs near the bay or in nitrogen-sensitive coastal areas face Title 5, local Board of Health, and watershed-protection considerations together.

Marion also has an active local Stormwater Management Bylaw under the federal MS4 Permit framework [Building Dept]. Any new construction may need stormwater design coordination. We pull the watershed map and the Board of Health requirements early so the design accounts for them from Day 1.

Do wetlands or conservation rules affect Marion ADUs?

Likely affects you if: your lot is within a wetland buffer, near a coastal resource area, a pond, a stream, or any mapped wetland.

Yes if your parcel falls within a wetland resource area buffer. The Marion Conservation Commission [Conservation] administers wetlands review under MGL c.131 §40 (the state Wetlands Protection Act) plus Marion's local wetlands bylaw [WPA]. Wetland filings are frequent for waterfront projects.

Adding an ADU near a wetland resource area triggers a Notice of Intent or Request for Determination filing. Plan on adding time to the schedule if your parcel falls within a buffer. Confirm the exact buffer distance with the Marion Conservation Commission.

Cost impact: +$5,000 to $15,000, plus 6 to 10 weeks of additional review for a waterfront or wetland-adjacent project.

How does the Marion aquifer overlay affect ADUs?

Likely affects you if: your parcel falls within an aquifer or Zone II wellhead protection overlay. Marion runs its own public water supply.

Marion has its own municipal water supply, and aquifer and Zone II wellhead protection overlays apply across parts of town [MassGIS]. ADU septic siting is reviewed more carefully inside these overlays, because adding a bedroom adds wastewater design flow and Zone II overlays limit how septic systems can be sited and sized.

A MassGIS overlay check on Day 1 tells you whether your parcel sits within an aquifer or wellhead protection zone. We pull this before quoting. In water-service areas, the draft Section 230-8.14 requires connection to the public water system, subject to DPW review [Section 230-8.14].

Do scenic road and tree rules affect Marion ADUs?

Likely affects you if: your project requires a driveway change or tree removal along a designated scenic road.

Marion has scenic road designations, and tree-cutting along a scenic road requires review [Building Dept]. This is a Marion-specific consideration that matters for any project requiring a driveway change or tree removal. We coordinate this early so it does not surprise the schedule.

Marion's historic village character also shapes design. ADUs in and around Marion Village are expected to fit the historic, residential, modest scale of the village, with Tabor Academy and other historic resources nearby. We design to match the village context.

What Does a Marion ADU Cost?

A Marion ADU should not be priced from square footage alone. Two similar ADUs can price very differently depending on sewer or septic status, coastal flood elevation, watershed and conservation review, and whether you build to the by-right 900 sq ft or the larger 1,200 sq ft option.

BuildX ADU Pricing $284,301 to $525,861

That is the full span of our 14 floor plans. Prices include the complete building package, foundation through move-in-ready finishes. Site work is priced separately after a lot evaluation.

Marion-specific cost premium factors

Septic upgrade (vs sewer) +$30,000 to $60,000 for outlying parcels on private septic
Coastal flood zone +15% to 25% along Sippican Harbor, the Buzzards Bay coastline, and Mattapoisett Harbor frontage (elevation, breakaway walls, engineer stamps)
Larger ADU (900 to 1,200 sq ft) Larger build cost; a Special Permit and additional local conditions apply to this Marion-specific range
Wetlands or Conservation review +$5,000 to $15,000, plus 6 to 10 weeks of additional review for waterfront or wetland-adjacent parcels
Stormwater Management Bylaw (MS4) Stormwater design coordination for new construction
Site access and utility run Variable impact. Backyard access, trenching distance for water, sewer, electric, and gas, equipment staging, and utility routing can change cost even when the ADU footprint stays the same. We map this on the Day 1 property review.

See full ADU pricing and floor plans. For a Marion-specific quote, call (781) 627-7000. We will not quote a Marion ADU until we know your sewer or septic status, Buzzards Bay watershed and flood-zone status, and whether you are building to 900 sq ft or the larger 1,200 sq ft option.

How the Marion ADU Permit Process Works

A by-right path for a protected-use ADU, plus a Special Permit step if you build larger than 900 sq ft.

Size determines the path. A protected-use ADU of 900 sq ft or less is by-right today under state law. If you build to the 900 to 1,200 sq ft range that Marion's draft Section 230-8.14 proposes, that is a Special Permit project with additional local conditions. Confirm the adopted bylaw status with the Building Department before committing to the larger size.
  1. 1

    Parcel review

    1 to 2 weeks

    BuildX maps your parcel against zoning, sewer or septic, FEMA flood zone, Buzzards Bay watershed, wetlands, and aquifer overlay status before quoting. This step determines whether the rest of the timeline is straightforward or extended. MassGIS and parcel overlay checks happen on Day 1.

  2. 2

    Building permit (protected-use ADU)

    Varies by completeness and town review queue

    For a protected-use ADU of 900 sq ft or less, submit a building permit application with a site plan and floor plan to the Marion Building Department through the town's Online Permitting system. In sewered areas, a DPW capacity review for the sewer or water connection is required per the draft Section 230-8.14 [Section 230-8.14] [DPW].

  3. 3

    Special Permit (only for 900 to 1,200 sq ft)

    Add a public hearing cycle when triggered

    If you build to the larger 900 to 1,200 sq ft range proposed in the draft bylaw, a Special Permit is required, which adds a public hearing and additional local conditions. This step does not apply to a protected-use ADU of 900 sq ft or less. Confirm the current Special Permit requirements with the Building Department.

  4. 4

    Overlay reviews (if triggered)

    Add weeks when triggered

    Title 5 septic review (MassDEP 310 CMR 15.000), Marion Conservation Commission filing for wetlands buffers (MGL c.131 §40 plus the local wetlands bylaw), Board of Health coordination for Buzzards Bay watershed and nitrogen-sensitive area concerns, FEMA flood compliance and engineer stamps for coastal parcels, and stormwater design under the MS4 Permit framework. These can run in parallel but can extend the critical path.

Construction inspections run through the Marion Building Department. Confirm the current permit process, turnaround, and Online Permitting platform at (508) 748-3516.

What Marion Zoning Districts Allow ADUs?

Marion's draft Section 230-8.14 allows ADUs as-of-right in all five Residence districts (A through E) and, unusually, in two business districts as well. Exact dimensional standards (lot size, frontage, setbacks, height) are set by the Marion Zoning Bylaw. Because the dimensional table is administered by the town and the bylaw is still in draft, confirm exact values with the Marion Planning Department for your specific parcel.

ADUs allowed in business districts (Marion-specific)

Section 230-8.14 explicitly allows ADUs as-of-right in the General Business and Marine Business districts, in addition to all five Residence districts. That is broader than most towns in our area, which allow ADUs only in residential districts. It can be useful if you own a residence in a mixed-use area or a Marine Business district property. Confirm how the draft applies to your specific parcel with the Planning Department [Section 230-8.14].

Residence A, B, C, D, E. The five residential districts.
  • Min lot: Per the Marion Zoning Bylaw. Confirm with the Planning Department.
  • Min frontage: Per the Marion Zoning Bylaw. Confirm with the Planning Department.
  • Max coverage: Per the Marion Zoning Bylaw. Confirm with the Planning Department.
  • Max height: Per the Marion Zoning Bylaw. Confirm with the Planning Department.

ADU rules (draft): ADUs allowed as-of-right in Residence A, B, C, D, and E. A protected-use ADU of 900 sq ft or less is by-right under state law. The 900 to 1,200 sq ft range requires a Special Permit per the draft Section 230-8.14 [Section 230-8.14].

What this means for your ADU: The Residence districts are the standard ADU case in Marion. Sewer or septic status, coastal flood exposure, and watershed considerations usually drive the design more than the base zoning. Confirm your parcel's exact dimensional limits with the Planning Department before design.

General Business and Marine Business. Business districts that allow ADUs.
  • Min lot: Per the Marion Zoning Bylaw. Confirm with the Planning Department.
  • Min frontage: Per the Marion Zoning Bylaw. Confirm with the Planning Department.
  • Max coverage: Per the Marion Zoning Bylaw. Confirm with the Planning Department.
  • Max height: Per the Marion Zoning Bylaw. Confirm with the Planning Department.

ADU rules (draft): Section 230-8.14 allows ADUs as-of-right in General Business and Marine Business, in addition to the Residence districts. Marine Business reflects Marion's coastal, harbor-oriented character [Section 230-8.14].

What this means for your ADU: If you own a residence in a General Business or Marine Business area, the draft bylaw gives you an ADU pathway most towns do not offer. Whether your specific use and parcel qualify is a Planning Department determination. Confirm before you design.

Overlay Districts. Aquifer, watershed, floodplain, scenic roads.

Aquifer and Zone II wellhead protection overlays, the Buzzards Bay watershed, FEMA floodplain areas along the coast, and scenic road designations all overlay the base districts. Overlays modify, but do not prevent, ADU construction.

Overlay analysis happens on Day 1 with MassGIS layers [MassGIS]. We pull your parcel's overlays before quoting.

Source: Marion draft Zoning Bylaw Section 230-8.14 (January 21, 2025) [Section 230-8.14]. Confirm adopted dimensional standards with the Marion Planning Department.

Sewer or Septic? Marion Is Mixed.

This is one of the biggest cost variables in any Marion ADU project. Marion has substantial public sewer in Marion Village (the central village). Outlying areas rely on private septic. The draft Section 230-8.14 requires connection to public sewer for ADUs in sewered areas, subject to DPW capacity review.

Marion Village (central) Substantial public sewer
Outlying residential areas Private septic
Coastal and nitrogen-sensitive areas Stricter septic review may apply
Show Title 5, water utility, and connection details
  • Water utility: Marion runs its own municipal water supply; aquifer and Zone II wellhead protection overlays apply [MassGIS]
  • Septic upgrade cost: $30,000 to $60,000 typical for an outlying parcel needing a system upgrade
  • Title 5 trigger: Adding a bedroom adds design flow, so Title 5 review is required on septic parcels [Title 5]
  • Sewer connection (draft): Required in sewered areas, subject to DPW capacity review per Section 230-8.14 [Section 230-8.14] [DPW]
  • Coastal nitrogen: Nitrogen-sensitive coastal area standards may apply near the bay. Confirm with the Marion Board of Health [Title 5]

Marion Village is largely sewered. Most outlying neighborhoods are on septic. We do not quote a Marion ADU until we know which side of that line your parcel sits on. A Title 5 inspection answers this question for your specific property, and the DPW confirms sewer capacity in sewered areas.

Marion Is Organized Around Its Harbor and Village

Marion is a small coastal town built around Sippican Harbor and the historic Marion Village. The areas that come up most often in ADU planning have their own sewer status, flood-risk profile, and design context. A Marion Village ADU is a different project from a Buzzards Bay coastline ADU.

Marion ADU Feasibility by Area (At a Glance)

Marion Area Common ADU Issue BuildX Note
Marion Village Sewer, historic village character Lower septic risk; design should fit the historic, modest village scale
Sippican Harbor area Coastal flood exposure, possible Marine Business district FEMA flood compliance and coastal premium drive design
Buzzards Bay coastline Flood zones, nitrogen-sensitive septic Watershed and Board of Health coordination matter early
Mattapoisett Harbor frontage Coastal flood exposure on the eastern boundary Elevation and FEMA flood rules may affect design
Outlying upland areas Septic, larger lots, scenic roads Title 5 capacity and any scenic-road tree review matter most
Marion Village Sewer

The central historic village, with the Town House at 2 Spring Street and Tabor Academy nearby. Largely sewered, with lower septic risk. ADUs here are expected to fit the historic, residential, modest village scale.

Flood risk: Moderate near the harbor.

Sippican Harbor area Coastal flood

The central harbor and waterfront. Coastal exposure with FEMA flood zones, and possible Marine Business district frontage. Coastal premium applies.

Flood risk: High along the water.

Buzzards Bay coastline Septic Coastal flood

Multiple coves, beaches, and tidal areas. Coastal premium, FEMA flood zones, and nitrogen-sensitive area septic considerations near the bay.

Flood risk: High. Cost premium 15% to 25%.

Mattapoisett Harbor frontage Coastal flood

The eastern coastal boundary, shared with Mattapoisett. Coastal exposure and FEMA flood compliance.

Flood risk: High along the water.

Outlying upland areas Septic

Larger lots away from the coast, with private septic and reserve area. Some parcels sit along designated scenic roads where tree removal requires review.

Flood risk: Low.

Marion is BuildX home territory. We work the South Coast every month. We know the Buzzards Bay watershed, the coastal flood zones, the sewer-and-septic line, and the draft 1,200 sq ft allowance. Ask us anything about your specific parcel.
Ask BuildX about your Marion lot

What Marion's Building Commissioner Says

Marion's draft bylaw came out of a public process, with the Building Commissioner on the record about why the old rules needed to change.

I personally think we should get rid of the old bylaw altogether because it doesn't allow rentals and it's only for family members, and I've been saying since I got here, "How do I regulate that?"
Bob Grillo Building Commissioner, Town of Marion Joint Planning Board and Select Board meeting, October 7, 2024, as reported by Sippican Week [Grillo, Oct 2024]

That is the operating posture behind Marion's draft Section 230-8.14: align the local rules with state law, allow rentals, and move past the old family-member-only accessory apartment rule. The draft bylaw and the joint board consensus reflect that direction. The final adopted text and the short-term-rental approach are still being confirmed. Confirm the current status with the Marion Building Department at (508) 748-3516.

Marion Building Department

Marion Building Department

Marion uses the term "Town House" rather than "Town Hall," a historic Marion convention. The Building Department is at the Marion Town House. The Building Commissioner and Town Planner work together on ADU policy, so on an ADU question it helps to ask for either one when you call [Building Dept].

Marion is a small, tightly-staffed town. For ADU questions, the Building Commissioner and Town Planner coordinate, so asking for either one when you call gets you to the right conversation.

Call Marion Building Dept Ask BuildX to check first
Questions to ask when you call Marion
  1. What is the current adopted status of Section 230-8.14, and is the 1,200 sq ft option available yet?
  2. Is my parcel in a sewered area, and is sewer connection required for the ADU?
  3. Will Title 5 review be required, and does my address sit in a nitrogen-sensitive coastal area?
  4. Is my parcel in a FEMA flood zone, an aquifer or wellhead overlay, or a wetland buffer?
  5. Is my property on or near a designated scenic road that would require tree-cutting review?
  6. How is the town handling short-term rentals and owner-occupancy under the draft bylaw?

Explore Marion ADU Topics

Jump to deep-dive sections on this page.

Marion ADU Zoning→ Permit Process→ Marion ADU Costs→ Size Limits→ All Rule Details→ Septic and Title 5→ Coastal Flood Zones→ Buzzards Bay Watershed→ Wetlands and Conservation→ Aquifer Overlay→ Scenic Roads and Trees→ Sewer or Septic→ Garage Conversions→

Marion ADU FAQs

Can I build an ADU in Marion right now?

Yes. A protected-use ADU of 900 sq ft or less is allowed by-right today under Massachusetts state law (760 CMR 71.00, effective January 31, 2025) in zones that permit single-family dwellings, subject to the building code and septic capacity. Marion is separately drafting a local bylaw, Section 230-8.14, that would allow ADUs up to 1,200 sq ft. Confirm the adopted status of that draft with the Building Department before planning to the larger size.

How big can a Marion ADU be?

Up to 900 sq ft is by-right under state law (or 50% of the principal dwelling, whichever is smaller, for a protected-use ADU). Marion's draft Section 230-8.14 proposes allowing ADUs up to 1,200 sq ft, with a Special Permit required for the 900 to 1,200 sq ft range. That larger range is not a protected-use ADU, so the town can attach local conditions to it. Confirm the adopted size limit with the Marion Planning Department.

Do I need a special permit for a Marion ADU?

Not for a protected-use ADU of 900 sq ft or less, which is by-right under state law. Marion's draft Section 230-8.14 would require a Special Permit only for the larger 900 to 1,200 sq ft range. Confirm the current requirements with the Building Department, since the bylaw is still in draft.

Can I build an ADU in a Marion business district?

Marion's draft Section 230-8.14 allows ADUs as-of-right in the General Business and Marine Business districts, in addition to all five Residence districts. That is broader than most towns in our area. Whether your specific parcel and use qualify is a Planning Department determination, and the bylaw is still in draft, so confirm before you design.

Can I Airbnb my Marion ADU?

That is being decided. Marion officials discussed allowing short-term rentals only when tied to owner-occupancy, which staff described as potentially workable subject to legal review. State law preempts owner-occupancy requirements for a protected-use ADU of 900 sq ft or less, but a town can regulate short-term rentals specifically. Long-term rental of a protected-use ADU is allowed under state law. Confirm the final adopted short-term-rental approach with the Marion Building Department.

Sewer or septic in Marion?

Depends on your parcel. Marion has substantial public sewer in Marion Village (the central village), while outlying areas rely on private septic. This is one of the biggest cost variables. A Title 5 capacity check plus possible system replacement adds $30,000 to $60,000 to a septic-served Marion ADU project. In sewered areas, the draft Section 230-8.14 requires connection to public sewer, subject to DPW capacity review. Confirm sewer availability by your specific address.

What about Buzzards Bay water quality?

Watershed protection is a real consideration in Marion. The Marion Town House hosts the mailing address for the Buzzards Bay Action Committee, the regional water-quality coalition. ADUs near the bay or in nitrogen-sensitive coastal areas face Title 5, local Board of Health, and watershed considerations together, and stricter septic standards may apply near the water. We pull the watershed map and Board of Health requirements early.

What does a Marion ADU cost?

BuildX ADU pricing ranges from $284,301 to $525,861. That covers the complete building package, foundation through move-in-ready finishes; site work is priced separately after a lot evaluation. Marion-specific drivers move a project within that band: septic upgrades add $30,000 to $60,000 on outlying parcels, coastal flood zones add 15% to 25% for elevation and engineer-stamped compliance, and building to the larger 900 to 1,200 sq ft range adds cost plus a Special Permit. For a property-specific quote, call (781) 627-7000.

Plymouth County or Bristol County?

Marion is in Plymouth County, not Bristol County like its neighbors Acushnet and Fairhaven. Deed recordings for Marion go to the Plymouth County Registry of Deeds in Plymouth [Plymouth Deeds]. It is a different deed registry workflow from the Bristol County towns just to the west.

Who do I call about building an ADU in Marion?

For official town process questions (permit requirements, fees, the adopted status of Section 230-8.14, Online Permitting help, building code interpretation), call the Marion Building Department at (508) 748-3516 and ask for the Building Commissioner or the Town Planner.

For parcel-level feasibility, cost estimates, design options, watershed and flood considerations, and construction planning, call BuildX at (781) 627-7000.

The two are different conversations. The town can tell you what is administratively required. BuildX can tell you what is realistic on your specific parcel and what it will actually cost to build.

Sources Reviewed

Last verified: September 20, 2026. Grouped by source type so you can see which claims come from town law, state law, town process, local constraints, and media records.

View all 19 sources, grouped
Town law
  1. Town of Marion. Section 230-8.14 Accessory Dwelling Units (draft, January 21, 2025). Up to 1,200 sq ft local extension, business-district allowance, conversion provisions, and sewer and water connection requirements. Confirm the current adopted status with the Building Department.
State law
  1. Commonwealth of Massachusetts. Accessory Dwelling Units (760 CMR 71.00). Protected-use ADUs. The regulation took effect January 31, 2025; the underlying ADU statute (Affordable Homes Act) took effect February 2, 2025.
  2. Commonwealth of Massachusetts. Accessory Dwelling Unit (ADU) FAQs. State guidance on ADU rules.
  3. Massachusetts General Laws. M.G.L. Chapter 40A, Section 3. Zoning Act as amended by the Affordable Homes Act (Chapter 150 of the Acts of 2024), ADU provisions.
  4. MassDEP. Title 5 (310 CMR 15.000) Compliance for ADUs FAQ. Relevant for outlying septic parcels and nitrogen-sensitive coastal areas.
  5. Massachusetts General Laws. M.G.L. Chapter 131, Section 40. Wetlands Protection Act.
Town process
  1. Town of Marion. Building Department. Marion Town House, 2 Spring Street; (508) 748-3516; Building Commissioner Bob Grillo; hours Monday to Thursday 8:00 AM to 4:30 PM, Friday 8:00 AM to 3:30 PM. Town House terminology, Stormwater Management Bylaw, and scenic road context.
  2. Town of Marion. Building Permit Information. Permit information; Fire Department burning-permit reference.
  3. Town of Marion. Conservation Commission and ADU legislation information. Town menu and ADU legislation context.
  4. Town of Marion. Department of Public Works. Sewer and water capacity review for ADU connections per Section 230-8.14.
Local constraints (watershed, conservation, aquifer, coastal)
  1. Buzzards Bay Action Committee (BBAC). Contact information. The regional water-quality coalition for the Buzzards Bay watershed; mailing address at the Marion Town House.
  2. Wikipedia and U.S. Census. Marion, Massachusetts. Population (about 5,000), coastal Plymouth County geography, Sippican Harbor, Tabor Academy, and historic village context.
  3. Census Reporter. Marion town profile. Demographics.
  4. Plymouth County Registry of Deeds. Plymouth County Registry of Deeds. Deed registry for Marion (Plymouth County).
  5. Town of Marion. Conservation Commission. Wetlands Protection Act and local wetlands bylaw filings for waterfront and wetland-adjacent projects. Confirm the current Conservation Commission page and filing requirements with the Marion Town House at (508) 748-3516.
  6. Town of Marion. Board of Health. Title 5 review and Buzzards Bay watershed and nitrogen-sensitive coastal area coordination. Confirm the current Board of Health page and requirements with the Marion Town House at (508) 748-3516.
  7. MassGIS, Bureau of Geographic Information. Aquifer and Zone II wellhead protection GIS layers. Aquifer and wellhead protection overlays.
  8. Federal Emergency Management Agency (FEMA). Flood Map Service Center. Marion coastal flood zone lookup (Sippican Harbor, Buzzards Bay coastline, Mattapoisett Harbor frontage).
Media and meeting records
  1. Sippican Week. Marion Mulls Accessory Dwelling Unit Bylaw. October 2024. Coverage of the joint Planning Board and Select Board meeting of October 7, 2024, documenting Building Commissioner Bob Grillo's statement on the old bylaw.

Nearby South Coast ADU Rules

Marion borders Wareham to the north and west, Mattapoisett to the east (sharing Mattapoisett Harbor), Rochester to the north, and Acushnet to the west across the county line. All four are home territory for BuildX, the same coastal neighborhoods we build in.

Wareham Wareham ADU rules Mattapoisett Mattapoisett ADU rules Rochester Rochester ADU rules Acushnet Acushnet ADU rules

ADU Rules by City in the BuildX Service Area

BuildX serves 40 towns across four areas of southeastern Massachusetts. Each city has its own ADU bylaw, sewer or septic split, overlay map, and Building Department contact. Jump to the rules for your town:

South Shore (22)

South Coast (9)

Upper Cape Cod (4)

Bridgewater Area (5)

Ready for a parcel-specific answer? A free Project Clarity Call gets you a one-pager covering zoning, sewer or septic, FEMA flood zone, Buzzards Bay watershed, wetlands, and aquifer status for your specific Marion address.
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Thinking about an ADU in Marion?

BuildX can review your Marion parcel for zoning, sewer or septic, FEMA flood zone, Buzzards Bay watershed, wetlands, and aquifer overlay issues before you spend money on design or permitting. Marion is BuildX home territory, so we know the constraints that drive your project, from the coastal flood zones to the draft 1,200 sq ft allowance.

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Disclaimer: The information on this page is drawn from live interviews, podcast episodes, municipal bylaws, planning board materials, town websites, and other publicly available sources, and reflects what was accurate as of the original recording or verification date. Pricing, timelines, materials, regulations, zoning rules, permit processes, fees, and overlay district boundaries can change -- sometimes without public notice -- and no two towns interpret or apply the rules the same way. This page is for informational purposes only and should not be relied upon as the basis for any purchasing, construction, or investment decision. BuildX makes no guarantee that the information is current or complete for your specific parcel. Before making any decisions, contact the town directly or call BuildX at (781) 627-7000 or schedule a Project Clarity Call to review your specific situation.