Greenwich ADU Zoning Guide

Last reviewed 2026-04-26

ADUs allowedYes
ApprovalBy-right
Max size800 sq ft
Owner occupancyRequired

Greenwich, CT permits Accessory Dwelling Units under §6-99 of its Building Zone Regulations, replaced in full by Text Amendment PLPZ 2023 00236 (effective July 14, 2023). The new rules use a two-track system — Internal ADU (within the existing house) and External ADU (a separate structure) — with size caps that differ by zone. External ADUs in R-12, R-7, and R-6 are capped at 800 sq ft; in RA-1 and R-20 at 1,000 sq ft; in RA-2 and RA-4 at 1,200 sq ft. Internal ADUs are capped at 35% of the primary unit's gross floor area in all zones. Owner-occupancy is required, though the CT Affordable Homes Act 2024 (effective February 2025) may have preempted that requirement.

Status

Currently allowed: Yes
Form of approval: By-right (administrative approval by Planning & Zoning staff for conforming proposals); Special Permit from Planning & Zoning Commission for larger-than-standard units or nonconforming lots
Governing ordinance section: Town of Greenwich Building Zone Regulations §6-99 Accessory Dwelling Units
Last amended: Effective July 14, 2023 (Text Amendment PLPZ 2023 00236)

Eligibility

Where ADUs are allowed

Zoning districts permitted: All single-family residential zones: RA-4, RA-2, RA-1, R-20, R-12, R-7, and R-6.
Lot type / use restrictions: Must be on a single-family residential property. In R-6 zone, the existing structure must be a single-family dwelling; existing two-family structures in R-6 are not eligible.
Minimum lot area required: Lot must conform to (or legally nonconform to) the minimum lot size of the applicable zone.
Limit per property: 1 ADU per property (either External or Internal)

Types allowed

Detached: Yes, in all residential zones subject to size limits by zone (External ADU — standalone structure)
Attached: Yes (classified as External ADU if in a separate structure; Internal ADU if within the primary structure) (addition sharing a wall)
Interior conversion: Yes — classified as an Internal ADU; size capped at 35% of the primary unit's gross floor area in all zones (basement, attic, within main house)
Garage conversion / detached accessory conversion: Conditional — permitted only if the required off-street parking is replaced elsewhere on the property.

Size and placement

Size limits

Zone	Max ADU size
R-12, R-7, R-6	800 sq ft

Maximum sq ft (External ADU, by zone): R-12, R-7, R-6: 800 sq ft
Maximum sq ft (Internal ADU, formula-based): 35% of the gross floor area of the Primary Unit, all zones
Maximum height: Accessory buildings in residential zones shall not exceed 25 feet; maximum stories varies by zone per §6-205

Setbacks

Zone	Min. Side Setback (accessory in rear yard)	Min. Rear Setback (accessory in rear yard)
RA-4	35 ft	35 ft
RA-2	25 ft	25 ft
RA-1	15 ft	15 ft
R-20	10 ft	10 ft
R-12	5 ft	5 ft
R-7, R-6	5 ft	5 ft

Front setback: No accessory building shall be located in any required front yard
Distance from primary structure: Not explicitly specified in §6-99; must be at least 5 ft from another structure per §6-144(a)
Coverage / open space requirements: ADU counts toward overall lot FAR and green area requirements; crawl spaces must be unfinished and are not counted as living space

Rules for use

Parking

Required spaces: At least one off-street parking space on an appropriate solid surface dedicated to the ADU
Exemptions: None specified
Tandem parking allowed: Yes — in the R-6 zone specifically, tandem parking under §6-155(1)(d) is permitted
Note: Greenwich opted out of CT Public Act 21-29's prohibition on parking requirements exceeding 1 space; the town retains its own local parking standard

Owner occupancy

Required: Yes
Specifics: "The owner of record must reside in either the ADU or the Primary Unit." The owner must retain title to both structures at all times.
Penalty for non-compliance: Approval is automatically revoked upon finding that the owner does not comply with the occupancy requirement or fails to file the required annual affidavit
Affidavit required at permit: Yes — an initial affidavit at the time of application AND an annual affidavit acknowledging continued compliance

Rental use

Long-term rental allowed: Yes — ADU may be rented to anyone at fair market rate; no affordability restriction required
Short-term rental (Airbnb/VRBO): No — Short-term Residential Rental of accessory units under §6-99 is expressly prohibited. The BZR defines short-term rental as fewer than 30 consecutive nights and specifically excludes ADUs from this use.
Sale of ADU separately from primary: No — the owner must retain title to both structures at all times

How to apply in Greenwich

Approving body: Planning & Zoning Department (administrative staff review for conforming proposals); Planning & Zoning Commission for Special Permit applications
Application type: Administrative zoning permit (by-right for conforming ADUs); Special Permit + public hearing for non-conforming lots or above-maximum sizes
Public hearing required: No, for conforming by-right applications. Yes, for Special Permit applications (full P&Z Commission review)
Typical timeline: "There is no single timeline. Simple homeowner jobs can be processed faster, while projects needing Zoning, Health, Fire Marshal, or DPW approvals can take weeks."
Application fee: Calculated at time of submission; not pre-published
Other inspections / certificates required: Certificate of Occupancy required; Health Department or DPW Sewer Division endorsement for septic/sewer capacity must be submitted prior to permit issuance; Fire Marshal sign-off for building code compliance
P&Z contact: 203-622-7894; 101 Field Point Road, Greenwich, CT 06830

State-level context

Connecticut Public Act 21-29 (2021). Greenwich opted out. The Planning & Zoning Commission voted to opt out, and the Representative Town Meeting (RTM) voted to approve the opt-out in September 2022. The town implemented its own updated §6-99 regulation effective July 14, 2023, which is materially more permissive than the old rules but customized to Greenwich's local conditions.

CT Affordable Homes Act (2024 / HB 6107). This 2024 state law includes provisions (Section 7 and 8) that redefine ADUs and, effective February 2025, allow the first ADU to be built by-right and remove the ability of towns to enforce owner-occupancy requirements. No primary source found confirming whether Greenwich has formally amended its §6-99 to reflect the removal of the owner-occupancy requirement mandated by the 2024 law. This is a flagged item — see §14 below.

Recent and pending changes

July 14, 2023
Major overhaul — Text Amendment PLPZ 2023 00236 replaced §6-99 in its entirety, creating a two-track (Internal/External) ADU system open to all zones and all tenants. Previously, ADUs were restricted to elderly/disabled or affordable tenants.
October 2022 – July 2023
Moratorium on the old §6-99 was in effect while the new regulation was drafted.
CT Affordable Homes Act 2024 (effective February 2025)
Statewide law removes municipal authority to enforce owner-occupancy as a condition of ADU permitting. Impact on Greenwich's local §6-99 owner-occupancy requirement is unclear — flagged as pending clarification (see §14).

Important details

FAR and green area: The ADU's floor area counts toward the property's FAR and green area requirements under §6-205. In RA-4 and RA-2 zones, green area requirements are 84% and 78% respectively — leaving limited buildable coverage.
No new curb cut: No additional driveway may be created primarily to serve the ADU; the existing driveway must serve both units.
Streetscape appearance rule: The ADU must not appear to convert the lot into a two-family property. For an Internal ADU, the front doors of the Primary Unit and ADU must not have equal visual prominence. For an External ADU, the portion visible from the street must retain subordinate massing.
Septic/sewer endorsement required before permit: If on private septic, the Health Department must endorse adequate capacity. If on town sewer, DPW Sewer Division endorsement is required. Both must be submitted to P&Z before a zoning permit is issued.
Special Permit path remains available: Even when a by-right application is possible, an owner may seek a Special Permit to build an ADU larger than the standard maximums, provided the P&Z Commission makes specific findings about compatibility.

Frequently asked questions

What is the maximum size for an external ADU in Greenwich?

External ADUs in all residential zones are limited to 800 square feet, though the Planning and Zoning Commission may approve up to 1,000 square feet upon demonstrated good cause.

Does Greenwich require owner occupancy for an ADU?

Yes, the owner must continue to occupy either the primary or accessory dwelling unit upon approval. This ensures the ADU remains secondary to the primary residence and maintains neighborhood character.

What parking and infrastructure requirements does Greenwich enforce?

At least one off-street parking space is required for the ADU. If the property is not on town sewers, you must obtain Health Department endorsement that the septic system is adequate; if on town sewers, you need DPW Sewer Division endorsement of adequate capacity.

Verify with the city before relying on these

These details aren’t published clearly online. Confirm with Greenwich before starting your project, or book a free consultation with our team — we’ll dig into the specifics for your lot.

Application fee amount: The town calculates permit fees at time of submission. Not pre-published online. Contact: Building Inspection Division, 101 Field Point Road, Greenwich, CT 06830 | bldginsp@greenwichct.gov | 203-622-7894
Impact of CT Affordable Homes Act 2024 on owner-occupancy requirement: The state's 2024 law (Section 7, effective February 2025) reportedly removes municipal authority to require owner-occupancy. It is unclear whether Greenwich has formally amended §6-99 to reflect this. Contact: Planning & Zoning Department, 203-622-7894 — ask specifically whether §6-99(3)(A) owner-occupancy requirement is still being enforced post-February 2025.
Maximum number of bedrooms in ADU: Not specified in §6-99. Contact: Planning & Zoning, 203-622-7894.
Separate utility metering: Not addressed in §6-99. Contact: Planning & Zoning, 203-622-7894.

Sources (11)

Text Amendment PLPZ 2023 00236 — Section 6-99 Accessory Dwelling Units (full adopted text) — Zoning text amendment — Effective 07/14/2023primary
Building Zone Regulations Division 9 (August 2023) — Zoning code — Accessed 04/2026primary
Building Zone Regulations Division 12 — Accessory Buildings — Zoning code sectionprimary
Schedule of Required Open Spaces §6-205 — Dimensional scheduleprimary
ADU Application Form 2024 — Application formprimary
Short-Term Rental Regulation BZR (adopted 01/20/2022, effective 01/27/2022) — Zoning text amendmentprimary
ADU Public Act 21-29 Opt-Out Draft Resolution — Municipal resolutionprimary
Greenwich Free Press: "P&Z Watch: Draft of Less Restrictive Reg Under Consideration" — News article — 05/09/2023primary
Greenwich Sentinel: "How to Increase the Value of Your Greenwich Property" — News/analysis — 01/2024primary
Zook Cabins: "ADU Regulations in Connecticut (2026 Guide)" — Third-party guide — 04/2026primary
BaintonRE: "Greenwich CT ADU Rules: A Homeowner's Guide 2025" — Real estate summary — 11/2025primary

Last reviewed 2026-04-26. Local rules can change — verify the latest details with the Greenwich planning department, or book a free consultation with our team before starting your project. This page is informational and is not legal advice.

Greenwich ADU regulations.