ADU Rules in Plymouth, MA
Yes. Plymouth allows ADUs by-right up to 900 sq ft. The friction is not zoning. It is septic capacity, flood-zone rules, historic-district review, and the two-step permit process.
Call BuildX: (781) 627-7000
Plymouth allows ADUs by-right
Town Meeting vote: 107 to 32 · Article 14Plymouth Town Meeting adopted Article 14 at the April 6, 2024 Annual Town Meeting [Bylaw] by a landslide margin (per Plymouth Independent coverage [Plymouth Independent]). The Planning Board approved 5 to 0 in October 2023. The Board of Health and Senior Task Force formally supported adoption. Detached, attached, and interior-conversion ADUs are allowed by-right in five residential districts up to 900 sq ft or 50% of the principal dwelling, whichever is smaller.
Can I build an ADU in Plymouth, MA?
Yes. Plymouth allows detached, attached, and interior-conversion ADUs by-right in RR, R-40, R-25, R-20SL, and R-20MF districts, up to 900 sq ft or 50% of the principal dwelling, whichever is smaller. No special permit is required if the project meets the criteria.
Show full bylaw, citation, and state preemption note
Plymouth's ADU bylaw lives in §201-3 (the definition) and §203-17 (the regulations), with the controlling vote being Article 14 of the April 2024 Annual Town Meeting [Bylaw]. The definition reads:
One narrow state preemption note. Plymouth's local definition (§201-3) includes the phrase "owner-occupied" in describing the principal dwelling associated with an ADU. Massachusetts state law (760 CMR 71.00, effective January 31, 2025) preempts owner-occupancy requirements for protected-use ADUs. So in practice, you may rent the principal dwelling and live in the ADU, or live in the principal dwelling and rent the ADU. This is a single-clause preemption, not a wholesale rejection of Plymouth's bylaw. The 900 sq ft cap, the two-step permit sequence, and the short-term-rental prohibition all stand and are enforceable.
Confirm Plymouth's current administrative posture on the owner-occupancy clause with the Building Department at (508) 747-1620 before signing a lease.
For most homeowners, the practical answer is straightforward. A Plymouth ADU at or under 900 sq ft, on a single-family lot in any of the five residential districts (RR, R-40, R-25, R-20SL, R-20MF), is a by-right project. You do not need a special permit. You do not need a public hearing. Plymouth Planning Board Chair Steven Bolotin confirmed the as-of-right path on WATD 95.9 FM in July 2025 [WATD]: where ADUs are permitted, they are allowed without a special permit.
What you do need is a clean two-step package. Step 1 is the zoning application: a site plan showing setbacks and dimensions, plus a floor plan with existing and proposed living space. Step 2 is the building permit: New Construction Application for a detached ADU, or Addition/Alteration Application for an attached or interior-conversion ADU. The Building Department will not accept your ADU building permit until your zoning permit is approved. Sequential, not simultaneous.
Plymouth runs the entire process through OpenGov Citizen Services, a 24/7 web-based platform. Where Plymouth ADU projects actually slow down is upstream of the Building Department: Title 5 capacity for septic-served properties (most of the town outside Plymouth Center), Conservation Commission filings inside the 100-foot wetland buffer, FEMA flood compliance for coastal parcels, and Plymouth Historic District Commission review where applicable.
Garage conversion ADU
A common variation of either the detached or attached ADU paths, depending on the garage configuration. Plymouth's bylaw does not treat garage conversion as a separate ADU category; it is classified based on whether the converted structure is structurally attached to the principal dwelling.
- If the garage is attached to the house: Treated as an attached ADU (Addition or Alteration Application)
- If the garage is detached from the house: Treated as a detached ADU (New Construction Application or major alteration)
- Best for: Properties with structurally sound existing garage; ability to reuse foundation, walls, roof; faster permitting than ground-up construction
- Watch for: Foundation adequacy, insulation upgrades, separate-entrance and bathroom plumbing additions, replacement of garage door with proper wall and window framing, parking compensation if the original parking spaces are lost
Plymouth ADU Rules at a Glance
The six things most homeowners ask first. Tap "View all rule details" for the complete data set.
View all Plymouth rule details (15+ data points)
- ADU types allowed: Detached, attached, interior conversion
- Districts allowed in: RR, R-40, R-25, R-20SL, R-20MF (5 residential)
- Default zone: R-25 (mid-density suburban Plymouth)
- Town Meeting vote: 107 to 32 (April 6, 2024 ATM)
- Planning Board: Approved 5 to 0 (October 2023)
- Owner-occupancy: Local clause preempted by 760 CMR 71.00
- Long-term rental: Allowed
- Sewer status: Split. Plymouth Center sewered, outlying septic
- Aquifer overlay: Yes (Zone II + Aquifer Protection District)
- Coastal flood zones: Harbor, Manomet, Saquish, White Horse Beach
- Setbacks (typical RR): 30 ft front, 10 ft side, 15 ft rear
- Max height: 35 ft, 2 stories
- Permitting platform: OpenGov Citizen Services (online 24/7)
- Setback source: Helsom and Chelsea Dias ZBA case (Feb 3, 2025) [ZBA]
- Bylaw sections: §201-3 (definition), §203-17 (regulations)
Why BuildX Knows Plymouth ADUs
Plymouth is BuildX's home base. We work Plymouth ADU projects every week and know the septic, flood-zone, historic-district, and conservation constraints that drive your project.
BuildX Home Base
Plymouth is BuildX home base. We are your neighbors, not a regional contractor. We build here, so we know Plymouth ADU parcels, zoning constraints, sewer or septic status, flood-zone issues, and historic-district 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, wetlands, aquifer overlay, and historic district status.
BuildX in Plymouth: 10 Real ADU Projects
Plymouth is BuildX home base. We are not a regional contractor visiting Plymouth, we are your neighbors. The list below carries each project's current status. We don't have a Plymouth division. The whole company IS Plymouth.
- Snyder (Completed): 610 GFA · 1-Bed, 1-Bath
- Myette (Completed): 900 GFA · 2-Bed, 1-Bath
- Farrell (Completed): 900 GFA · 2-Bed, 1-Bath
- Barber (Completed): 900 GFA · 2-Bed, 1-Bath, 2 Car Garage Under
- Creighton (Completed): 900 GFA · 2-Bed, 1-Bath
- Fabricius (Under Construction): 900 GFA · 2-Bed, 1-Bath
- Welker (Under Construction): 900 GFA · 1-Bed, 1-Bath
- Peters (Under Construction): 900 GFA · 1-Bed, 1-Bath
- Shanahan (Pre-Construction): 900 GFA · 2-Bed, 2-Bath
- Hart (Pre-Construction): 900 GFA · 2-Bed, 1-Bath
Real families. Real builds. Real ADUs on the South Shore. See more BuildX ADU builds →
What Can Complicate a Plymouth ADU?
Plymouth covers about 134 square miles, roughly the size of Boston. Your parcel's overlays, not the bylaw, are usually what move project cost and timeline. The six factors that come up most often:
Do I need septic approval for a Plymouth ADU?
Likely affects you if: your parcel is in Cedarville, Manomet, Chiltonville rural areas, Saquish, White Horse Beach, or any address not connected to municipal sewer. Roughly half of Plymouth is on private septic.
Yes if your parcel is on private septic. Cedarville, Manomet, Chiltonville (rural areas), Saquish, and White Horse Beach are on private septic. Adding a bedroom adds wastewater design flow, so a Title 5 inspection and capacity check are typically required before the ADU permit is approved.
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.
Plymouth Center and most of North Plymouth are on municipal sewer through Plymouth's Wastewater District (§206-5). Parcels inside the Municipal Wastewater District (MWD) are eligible for sewer connection. Parcels outside are on septic.
What flood-zone rules affect Plymouth ADUs?
Likely affects you if: your parcel is in Plymouth Harbor frontage, Manomet coast, Saquish, White Horse Beach, or any other coastal or low-lying parcel mapped in a FEMA flood zone.
Plymouth has 36 miles of Cape Cod Bay coastline. Significant FEMA flood zones run along Plymouth Harbor, Manomet, Saquish, and White Horse Beach. 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, utility elevation.
Sea level rise and erosion concerns also affect long-term planning for these parcels. Engineer-stamped flood compliance is non-negotiable on the permit side.
Do historic district rules apply to Plymouth ADUs?
Likely affects you if: your parcel sits inside Plymouth Center Historic District or in proximity to Cole's Hill, Burial Hill, or other parcels mapped in a Plymouth Historic District Commission boundary.
Yes if your parcel is in the Plymouth Center historic core. Plymouth Center is one of the oldest neighborhoods in Massachusetts: the original Pilgrim settlement, the Plymouth Rock waterfront, and the cluster of structures around Burial Hill and Cole's Hill that anchor a National Historic Landmark plus four NRHP districts and 20 individual NR listings.
- National Historic Landmarks: 1 (Cole's Hill, 1960; NRHP-listed 1966)
- NRHP Districts: 4 (incl. Plymouth Center Historic District, 1999)
- NRHP Individual Listings: 20 (incl. Burial Hill Cemetery, listed 2013)
- Local Authority: Plymouth Historic District Commission
- Cost premium: +10% to 15% when triggered
Detached ADUs in the historic core face additional design review through the Plymouth Historic District Commission. Massing, materials, fenestration, and roof form get scrutinized. It is not a denial mechanism. It adds time and cost on the central parcels.
Beyond the historic core, Plymouth's heritage tourism economy (Plimoth Patuxet Museums, Pilgrim Hall Museum, Mayflower II) is anchored in Plymouth Center. ADUs near Plimoth Patuxet have tourism-rental potential on paper, but Plymouth's town-wide STR prohibition under §201-3 clause 2 limits ADU rentals to long-term housing only.
Do wetlands or conservation rules affect Plymouth ADUs?
Likely affects you if: your lot is within 100 feet of any wetland, pond, cranberry bog, stream, coastal resource area, or mapped wetland buffer zone. Plymouth has 365 inland ponds and 36 miles of coastline, so many parcels qualify.
Yes if your parcel falls within 100 feet of a wetland resource area. The Plymouth Conservation Commission administers wetlands review under MGL c.131 §40 (the state Wetlands Protection Act) plus Plymouth General Bylaws Chapter 196 (the local wetlands bylaw, which extends regulatory jurisdiction beyond the state baseline). The local buffer is 100 feet from any wetland resource area.
Adding an ADU near a wetland resource area triggers a Notice of Intent or Request for Determination filing. Even septic system repairs in 100-foot buffer zones require Conservation Commission filings. Plan on adding 30 to 90 days to the timeline if your parcel falls within the buffer.
Cost impact: +$5,000 to $15,000, plus 30 to 90 days of additional review.
Plymouth has approximately 18,200 acres of protected open space across 65,000 total acres (about 28%), plus 365 inland ponds, 36 miles of coastline, and 32 globally rare coastal plain ponds. Plymouth ranks third in Massachusetts for rare, threatened, and endangered species per square mile [Pollinator Pathway]. Major holdings include Myles Standish State Forest (12,000 acres, shared with Carver, managed by MA DCR), Plymouth Town Forest (317 acres, 2007 conservation restriction), Halfway Pond Conservation Area, Davis-Douglas Conservation Area, South Triangle Pond Conservation Area, Russell Mill Pond Conservation Area, Foothills Preserve, and Town Brook watershed lands.
How does the Plymouth aquifer overlay affect ADUs?
Likely affects you if: your parcel falls within Zone II wellhead protection or the §206-1 Aquifer Protection District. Significant portions of Plymouth sit over the Plymouth-Carver Sole Source Aquifer.
Plymouth sits over the Plymouth-Carver Sole Source Aquifer, designated by the U.S. EPA on August 7, 1990 under Section 1424(e) of the Safe Drinking Water Act (Federal Register 55 FR 32137) [EPA] [Fed. Reg.]. The aquifer covers approximately 140 square miles under Plymouth, Carver, Kingston, Wareham, Plympton, Middleborough, and Bourne, and contains over 500 billion gallons of fresh water [USGS, 1992]. It is the second-largest sole-source aquifer in Massachusetts [UMass Boston UHI, 2008] and the only source of drinking water for residents in the seven-town service area.
The Plymouth Zoning Bylaw covers this through §206-1 (Aquifer Protection District) and multiple Zone II wellhead protection overlays. ADU septic siting is reviewed more carefully here than in most South Shore towns. 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 [MassGIS] tells you whether your parcel sits within Zone II or the Aquifer Protection District. We pull this before quoting.
Watershed coordination: Plymouth shares some watershed concerns with Carver and Wareham, including Cape Cod Bay nitrogen reduction in some MassDEP watershed permits. Properties along shared watershed lines may face additional MassDEP coordination, particularly around nitrogen-loading calculations on septic systems.
Inland flood territory exists along the major pond and stream networks (Halfway Pond, Long Pond, Russell Mill Pond, Town Brook). Plymouth's zoning bylaw includes a Floodplain Overlay across areas designated by FEMA.
Does Kingston Station affect Plymouth ADU parking?
Likely affects you if: your parcel is in northern Plymouth near the Kingston town line and the Kingston commuter rail station, or if your ADU adds bedrooms beyond the existing parking capacity.
Plymouth itself does not have a commuter rail station within town limits. The closest station is Kingston Station, located in neighboring Kingston on the Old Colony / Kingston-Plymouth Line. The station sits right on Plymouth's northern border.
Properties within 0.5 miles of Kingston Station, including parcels in Plymouth's northernmost areas near the Kingston town line, may qualify for the state's transit-adjacent parking exemption under MBTA Communities Act provisions. That can mean fewer required off-street parking spaces for an ADU. Worth checking your parcel's distance via MassGIS if you are in northern Plymouth.
Plymouth's ADU parking rule (per §201-3) is keyed to total bedroom count on the lot, not a fixed spaces-per-ADU formula. Adding an ADU bedroom adds parking demand under that formula unless the transit exemption applies.
What Does a Plymouth ADU Cost?
A Plymouth ADU should not be priced from square footage alone. Two 800 sq ft ADUs can price very differently depending on septic capacity, flood elevation, conservation review, historic-district design requirements, and site access.
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.
Plymouth-specific cost premium factors
See full ADU pricing and floor plans. For a Plymouth-specific quote, call (781) 627-7000. We will not quote a Plymouth ADU until we know your specific neighborhood, sewer or septic status, flood zone, and overlay status.
How the Plymouth ADU Permit Process Works
Two sequential permits, not one. Both by-right.
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1
Parcel review
1 to 2 weeks
BuildX maps your parcel against zoning, sewer or septic, FEMA flood zone, wetlands, aquifer overlay, and historic district status before quoting. This is the step that determines whether the rest of the timeline is straightforward or extended. MassGIS / parcel overlay checks happen on Day 1.
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2
Zoning permit
Varies by completeness and town review queue, typically 30 to 60 days
Submit site plan (showing setbacks and dimensions) and floor plan (existing and proposed living space) to the Plymouth Building Department through OpenGov Citizen Services. The Building Department will not accept your building permit application until your zoning permit is approved. Zoning approval is by-right (no special permit, no public hearing) for ADUs at or under 900 sq ft.
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3
Building permit
30 to 60 days after zoning approval
File the New Construction Application for a detached ADU, or the Addition or Alteration Application for an attached or interior conversion ADU. Submitted through OpenGov.
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4
Overlay reviews (if triggered)
Add 30 to 90+ days when triggered
Title 5 septic review (MassDEP 310 CMR 15.000), Plymouth Conservation Commission filing for wetlands buffer (MGL c.131 §40 plus Chapter 196), Plymouth Historic District Commission review for historic-core parcels, FEMA flood compliance and engineer stamps for coastal parcels. These run in parallel with the building permit but can extend the critical path.
Overall planning assumption: 90 to 120 days from contract signing to construction start for a clean parcel with no overlay triggers. Add 30 to 90+ days for any of the overlay reviews above.
After permits issue, construction inspections run through the Plymouth Building Department. Confirm current administrative posture at (508) 747-1620.
What Plymouth Zoning Districts Allow ADUs?
Plymouth has five residential districts where ADUs are allowed by-right under Article 14. R-25 is the default residential zone for mid-density Plymouth. Dimensional schedules below come from §205-2 through §205-6 of the Plymouth Zoning Bylaw (October 2024 amended copy). All five districts permit detached, attached, and interior-conversion ADUs.
RR · Rural Residential. Largest-lot rural.
- Min lot: 60,000 sq ft
- Min frontage: 200 ft
- Max coverage: 20%
- Max height: 35 ft
Where: Cedarville, Halfway Pond area, Long Pond, southern and western Plymouth.
ADU rules: Detached, attached, and interior-conversion ADUs allowed by-right up to 900 sq ft. Setbacks for ADUs (30 ft front, 10 ft side, 15 ft rear) confirmed in Helsom and Chelsea Dias ZBA case (Feb 3, 2025) for the RR district [ZBA Minutes].
What this means for your ADU: Larger lots can help with detached ADU placement and visual separation from the main house. The most common review issues on RR parcels are septic capacity, wetlands buffers, and long utility runs from the street to the build site.
R-40 · Large Lot Residential. About 1 acre minimum.
- Min lot: 40,000 sq ft
- Min frontage: 175 ft
- Max coverage: 25%
- Max height: 35 ft
Where: Outlying suburban neighborhoods.
ADU rules: Detached, attached, and interior-conversion ADUs allowed by-right up to 900 sq ft.
What this means for your ADU: Roughly one acre of land usually leaves room to site a detached ADU without setback gymnastics. Utility connections, septic capacity, and any overlay districts (aquifer, wetlands) still drive feasibility more than the zoning rules themselves.
R-25 · Medium Lot Residential Common Plymouth residential zone
- Min lot: 25,000 sq ft
- Min frontage: 150 ft
- Max coverage: 30%
- Max height: 35 ft
Where: Mid-density suburban Plymouth, the most common residential designation in town.
ADU rules: Detached, attached, and interior-conversion ADUs allowed by-right up to 900 sq ft. Most common Plymouth ADU district.
What this means for your ADU: R-25 is the most common Plymouth residential ADU case. Setbacks, lot coverage limits, and your sewer or septic status drive most of the design decisions. Most R-25 parcels have enough room for a 900 sq ft detached ADU once setbacks are mapped.
R-20SL · Small Lot Residential. Higher density.
- Min lot: 20,000 sq ft
- Min frontage: 125 ft
- Max coverage: 35%
- Max height: 35 ft
Where: Older neighborhoods near Plymouth Center, North Plymouth, harbor area.
Footnote 3 of §205-5: Lots between 15,000 and 20,000 sq ft with a minimum 75 ft lot width are allowed if a pre-existing nonconforming single-family dwelling is on the parcel [Planning Board, Sep 2025].
ADU rules: Detached, attached, and interior-conversion ADUs allowed by-right up to 900 sq ft.
What this means for your ADU: Smaller lots make setbacks, lot coverage, and parking layout the design constraints to solve first. An interior conversion or attached ADU is often the right answer on tight R-20SL parcels. Footnote 3 of §205-5 may also allow ADUs on lots between 15,000 and 20,000 sq ft with a pre-existing nonconforming single-family dwelling.
R-20MF · Multifamily Residential
- Min lot: 20,000 sq ft
- Min frontage: 125 ft
- Max coverage: 35%
- Max height: 35 ft
Where: Areas zoned for multifamily housing.
ADU rules: Permits multifamily housing in addition to single-family. ADUs are allowed by-right on single-family lots within this district up to 900 sq ft.
What this means for your ADU: If you own a single-family home in an R-20MF district, you can build an ADU under the same rules as the other residential districts. The multifamily zoning of the district does not change the ADU-on-single-family-lot rules. Existing use and parcel configuration still need parcel-level review.
Overlay Districts. Aquifer, Wastewater, Floodplain, Historic.
Aquifer Protection District (§206-1), Municipal Wastewater District (§206-5), Floodplain Overlay, Plymouth Center Historic District. Overlays modify, but do not prevent, ADU construction.
Overlay analysis happens on Day 1 with MassGIS layers. We pull your parcel's overlays before quoting.
Sewer or Septic? Plymouth Is Split.
This is the single biggest cost variable in any Plymouth ADU project. Plymouth Center and most of North Plymouth are on municipal sewer through Plymouth's Wastewater District (§206-5). Cedarville, Manomet, Chiltonville (rural), Saquish, and White Horse Beach are on private septic.
Show Title 5, water utility, and aquifer details
- Water Utility: Plymouth Water Department, multiple Zone II wellhead protection overlays
- Septic upgrade cost: $30,000 to $60,000 typical
- Title 5 trigger: Adding a bedroom adds design flow, so Title 5 inspection required on septic parcels
- Wastewater District: §206-5 defines MWD eligibility
- Aquifer: Plymouth-Carver Sole Source Aquifer (EPA 1990) [EPA]
Plymouth Center is sewered. Most other neighborhoods are on septic. We do not quote a Plymouth ADU until we know which side of that line your parcel sits on. A Title 5 inspection answers this question for your specific property.
Plymouth Is Seven Markets in One
Plymouth covers about 134 square miles. The seven neighborhoods that come up most often in ADU planning conversations have their own sewer status, flood-risk profile, and design context. A Cedarville ADU is a different project from a Manomet ADU.
Plymouth ADU Feasibility by Area (At a Glance)
| Plymouth Area | Common ADU Issue | BuildX Note |
|---|---|---|
| Plymouth Center | Historic district, sewer access, tight lots | Design review and historic context drive design decisions |
| North Plymouth | Sewer, transit proximity, smaller lots | Parking layout and lot fit need parcel-level review |
| Manomet | Septic, coastal flood exposure | Title 5 capacity and flood compliance can drive cost |
| Cedarville | Septic, rural lots, utility runs | Septic capacity and utility distances matter most |
| Chiltonville | Septic, rural constraints, wetlands | Parcel-level review is important early in the process |
| White Horse Beach | Septic, coastal flood exposure | Elevation and FEMA flood rules may affect design |
| Saquish is an isolated peninsula with limited year-round residential building activity and is reviewed case by case. See the Saquish neighborhood card below for context. | ||
Plymouth Center Sewer
Town Center, historic, denser, sewered. Plymouth Center Historic District triggers design review for ADUs in the historic core.
Flood risk: Moderate.
North Plymouth Sewer
Denser, near Plymouth Harbor, primarily sewered. Older R-20SL housing stock common.
Flood risk: Moderate.
Chiltonville Mixed
Historic, oldest part of town, near Plymouth Center. Mixed sewer and septic depending on parcel location.
Flood risk: Low.
Cedarville Septic
Pine barrens, cranberry bogs, near the Cape Cod Canal. Sandy soils plus high water tables in places equal septic engineering challenges.
Flood risk: Low.
Manomet Septic High flood
Coastal cliffs, beach community. FEMA flood zones along Cape Cod Bay. Engineer-stamped flood compliance required.
Flood risk: High. Cost premium 15% to 25%.
Saquish Septic Very high
Coastal, isolated peninsula. Heavy FEMA flood-zone exposure. Sea level rise concern.
Flood risk: Very high. Project cost premium 15% to 25%.
White Horse Beach Septic High
Coastal, summer-resort character. Tight lots common. FEMA flood compliance and elevation requirements.
Flood risk: High.
What Plymouth's Planning Board Chair Says
When the Planning Board Chair who steered the bylaw goes on local radio to tell homeowners the path is by-right, the path is by-right.
where they're permitted they're allowed to go without a special permit
That is the operating posture of the Town of Plymouth. If you meet the criteria (residential or mixed-use district, single-family lot, 900 sq ft cap, 50% gross floor area, the bylaw's setback and parking rules), you go straight to the Building Department through the two-step zoning-then-building sequence. No special permit. No public hearing. The Planning Board Chair reinforced this on the record fifteen months after the April 2024 Town Meeting vote.
Plymouth Building Department
Plymouth Building Department / Inspectional Services
- Address26 Court Street, Plymouth, MA 02360
- Phone(508) 747-1620
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Hours
Monday7:30 AM to 4:00 PMTuesday7:30 AM to 6:30 PMWednesday7:30 AM to 4:00 PMThursday7:30 AM to 4:00 PMFriday7:30 AM to 12:00 PM
- Inspector windowMonday to Friday, 7:30 to 9:30 AM in office. In the field after 9:30 AM. Best window for live calls.
- Online permittingOpenGov Citizen Services (web-based, available 24/7).
- Building Departmentplymouth-ma.gov/351/Building
- Town ADU pageplymouth-ma.gov/1342/Accessory-Dwelling-Unit-ADU-Information
- Assessor databasegis.vgsi.com/plymouthma
Plymouth's Inspectional Services Department mission emphasizes safety, integrity, professionalism, transparency, and community engagement. The Tuesday evening extended hours are unusual for a Massachusetts building department and worth using for evening conversations.
Questions to ask when you call Plymouth
- Is my parcel in one of the eligible residential zoning districts (RR, R-40, R-25, R-20SL, R-20MF)?
- Do I need zoning permit approval before submitting the building permit?
- Is my property sewered or on septic?
- Will Title 5 review be required?
- Is my parcel in a flood zone, historic district, wetland buffer, or aquifer overlay?
- How is Plymouth currently applying the owner-occupancy clause after 760 CMR 71.00?
Explore Plymouth ADU Topics
Jump to deep-dive sections on this page.
Plymouth ADU FAQs
Can I build a detached ADU in Plymouth?
Yes, by-right. Plymouth Town Meeting adopted Article 14 of the April 6, 2024 Annual Town Meeting by a 107 to 32 vote. The Planning Board approved 5 to 0. The Board of Health and Senior Task Force formally supported the bylaw. Detached, attached, and interior-conversion ADUs are all permitted by-right in five residential districts (RR, R-40, R-25, R-20SL, R-20MF) up to 900 square feet.
Do I need a special permit for a Plymouth ADU?
No. Plymouth Planning Board Chair Steven Bolotin confirmed on WATD 95.9 FM in July 2025 that where ADUs are permitted, they are allowed without a special permit. Plymouth uses a two-step administrative process: a zoning permit first, then a building permit. No special-permit hearing, no public review.
Do I need to live there?
Plymouth's local bylaw §201-3 requires owner-occupancy, but state law (760 CMR 71.00, effective January 31, 2025) preempts owner-occupancy requirements for protected-use ADUs. In practice, you may rent the principal dwelling and live in the ADU, or live in the principal dwelling and rent the ADU. Confirm current operating posture with the Plymouth Building Department at (508) 747-1620 before signing a lease.
Can I Airbnb my Plymouth ADU?
No. Plymouth's bylaw §201-3 clause 2 prohibits using an ADU as a short-term rental as defined by MGL c. 64G. State law allows local STR restrictions, so Plymouth's prohibition is enforceable. If your business model is Airbnb or VRBO, Plymouth is not your town. Long-term rentals are fine.
How big can a Plymouth ADU be?
Up to 900 square feet, or up to 50% of the principal home's gross floor area, whichever is smaller. This is the same cap as state by-right protection under 760 CMR 71.00, so Plymouth's local rule and state law align on size.
Sewer or septic in Plymouth?
Depends on neighborhood. Plymouth Center and most of North Plymouth are on municipal sewer through Plymouth's Wastewater District (§206-5). Cedarville, Manomet, Chiltonville (rural areas), Saquish, and White Horse Beach are on private septic. This is the single biggest cost variable. A Title 5 capacity check plus possible system replacement adds $30,000 to $60,000 to a septic-served Plymouth ADU project.
What does a Plymouth 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. Plymouth-specific drivers move a project within and beyond that band: coastal flood zone parcels (Manomet, Saquish, White Horse Beach) add 15% to 25% for elevation, breakaway walls, and engineer-stamped flood compliance. Plymouth Center historic district adds 10% to 15% for design review. Septic upgrades add $30,000 to $60,000. For a property-specific quote, call (781) 627-7000.
How long does a Plymouth ADU permit take?
Plan on 90 to 120 days for the two-step zoning and building permit sequence combined, plus additional time for Title 5 review, Conservation Commission filings within wetland buffer zones (100 ft under MGL c.131 §40 and Plymouth General Bylaws Chapter 196), and historic district design review where applicable. Plymouth uses OpenGov Citizen Services for online permit submission, available 24/7.
Who do I call about building an ADU in Plymouth?
For official town process questions (permits, fees, inspector availability, OpenGov account help, building code interpretation), call the Plymouth Building Department and Inspectional Services at (508) 747-1620.
For parcel-level feasibility, cost estimates, design options, neighborhood-specific 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.
Can I build an ADU on septic in Plymouth?
Possibly. The existing septic system must have capacity under Title 5 (Massachusetts state regulations on subsurface sewage disposal, 310 CMR 15.000) to handle the additional bedroom that an ADU typically adds. Adding a bedroom adds wastewater design flow, and Title 5 calculates whether the system can carry it.
Many Plymouth neighborhoods outside Plymouth Center and most of North Plymouth rely on private septic systems. This includes Cedarville, Manomet, Chiltonville rural areas, Saquish, and White Horse Beach. If your existing system lacks capacity, an upgrade or full replacement adds $30,000 to $60,000 or more to the project cost.
The first thing BuildX does on a Plymouth septic property is pull the Title 5 records and assess capacity before any design work begins. This is part of the Property Review.
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 28 sources, grouped
- Town of Plymouth. Plymouth Zoning Bylaw (October 2024 amended copy). §201-3, §203-17, §205-2 through §205-6, §206-1, §206-5.
- Town of Plymouth. Accessory Dwelling Unit Bylaw (Article 14, April 2024 ATM). Vote: 107 in favor, 32 against. Planning Board 5 to 0.
- Town of Plymouth. Plymouth Zoning. Two-step permit sequence per §202-2.
- Town of Plymouth. Accessory Dwelling Unit (ADU) Information. Town's homeowner-facing ADU information page.
- Commonwealth of Massachusetts. Accessory Dwelling Units (760 CMR 71.00). Effective January 31, 2025 (state ADU regulations).
- Massachusetts General Laws. M.G.L. Chapter 40A, Section 3. Affordable Homes Act ADU provisions.
- MassDEP. Title 5 (310 CMR 15.000) Compliance for ADUs FAQ.
- Town of Plymouth. Plymouth Building Department. Hours, contact information, OpenGov Citizen Services platform.
- Town of Plymouth. Plymouth Inspectional Services. Building Commissioner roster, inspector schedule, and inspector-window office hours (Monday through Friday 7:30 AM to 9:30 AM in office; field after 9:30 AM).
- Town of Plymouth. Permit and License Applications. Download forms for New Construction Application (detached ADU) and Addition or Alteration Application (attached or interior-conversion ADU).
- Plymouth Department of Public Works. Public Works. Municipal Wastewater District service area per §206-5.
- Plymouth Zoning Board of Appeals. ZBA Minutes, February 3, 2025. Confirms 35-foot maximum height in R-20SL district.
- Plymouth Zoning Board of Appeals. ZBA Minutes, February 3, 2025. Helsom and Chelsea Dias case (RR 10-foot side setback confirmation).
- Plymouth Planning Board. Planning Board Agenda, September 10, 2025. References §205-5 footnote 3 for R-20SL district.
- U.S. Environmental Protection Agency, Region 1. Plymouth/Carver Sole Source Aquifer. EPA designation under Section 1424(e) of the Safe Drinking Water Act, effective August 7, 1990 (Federal Register 55 FR 32137).
- U.S. Environmental Protection Agency. Plymouth/Carver Federal Register Notice. EPA Regional Administrator's findings on sole-source aquifer designation, dated July 31, 1990. Public hearing held January 10, 1990, Plymouth, MA.
- U.S. Geological Survey, 1992. Geohydrology and simulated ground-water flow, Plymouth-Carver aquifer, southeastern Massachusetts. Documents the Plymouth-Carver aquifer at approximately 140 square miles, the second-largest in areal extent in Massachusetts. Reports 500+ billion gallons of fresh water under Plymouth, Carver, Kingston, Wareham, Plympton, Middleborough, and Bourne.
- Massachusetts GIS (MassGIS). EPA Designated Sole Source Aquifers data layer. Authoritative state geographic record of MA sole-source aquifer boundaries; identifies seven SSAs in Massachusetts including the Plymouth-Carver designation.
- Urban Harbors Institute, University of Massachusetts Boston, 2008. Plymouth-Carver Sole Source Aquifer: Regional Open Space Plan. Multi-town regional plan for the seven aquifer-area towns: Plymouth, Carver, Kingston, Wareham, Plympton, Middleborough, and Bourne. Contracted by Massachusetts Executive Office of Energy and Environmental Affairs.
- Pollinator Pathway. Plymouth Pollinator Pathway. Approximately 28% of 65,000 acres protected. 365+ ponds. 32 globally rare coastal plain ponds.
- Town of Plymouth. Historic Listings and Designations. 4 NRHP districts. 20 individual NR listings. 1 NHL.
- Massachusetts DCR. Myles Standish State Forest. Approximately 12,000 acres in Plymouth and Carver.
- Town of Plymouth. Plymouth Town Forest. 317 acres. 2007 conservation restriction.
- Wildlands Trust. Halfway Pond Conservation Area.
- Wildlands Trust. Davis-Douglas Conservation Area.
- See Plymouth. South Triangle Pond Conservation Area.
- Plymouth Independent. Town Meeting gets down to business. April 7, 2024. Coverage of April 6, 2024 Annual Town Meeting Article 14 vote (107 to 32, with one abstention, in favor of ADU bylaw). Reporting by Andrea Estes, Fred Thys, and Michael Cohen.
- WATD 95.9 FM. Accessory Dwelling Units (ADUs) Gaining Popularity in Plymouth. July 2025 interview with Planning Board Chair Steven Bolotin (source for the quote).
Nearby South Shore ADU Rules
Plymouth borders Carver to the west (sharing Myles Standish State Forest), Kingston to the north (location of the Kingston/Plymouth commuter rail station), Plympton to the northwest, and Bourne to the southeast across the Cape Cod Canal. All four are home territory for BuildX, the same neighborhoods we build in.
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)
Bridgewater Area (5)
Thinking about an ADU in Plymouth?
BuildX can review your Plymouth parcel for zoning, sewer or septic, FEMA flood zone, wetlands, aquifer overlay, and historic-district issues before you spend money on design or permitting. Plymouth is BuildX home base, so we know the constraints that drive your project and the path through the two-step permit process.
See our ADU project portfolio or visit the ADU Home TourDisclaimer: 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.