Greenwich's zoning regulations are relatively welcoming to ADUs, creating solid opportunities for homeowners seeking to maximize their property value. Whether you're considering a rental unit to supplement household income, additional space for aging parents or adult children, or a detached home office and guest suite, understanding the local zoning rules is essential to moving forward with confidence. We've reviewed Greenwich's zoning regulations in detail and outlined the key requirements below. Rules can change, so confirm details with the Greenwich Planning Department or book a free consultation with our team before starting your project.
Where Are ADUs Allowed
ADUs in Greenwich are permitted on single-family residential properties. ADUs are permitted on single-family residential properties that meet current zoning district requirements.Each property is limited to one ADU. Key neighborhoods where ADUs are often approved include Cos Cob, Riverside, Old Greenwich.
Types of ADUs Allowed
Attached (an addition to your existing home that shares a wall, maintaining architectural cohesion with the main structure). Detached (a standalone structure in your backyard, ideal for rental income, multigenerational living, or maximum privacy). Converted (repurposing an existing garage, basement, or accessory structure, often the most expedient option since the shell already exists).
Size Limits
ADU size must comply with Greenwich's local zoning requirements. Contact the Greenwich Planning Department for specific square footage limits.
Parking
Off-street parking requirements apply to ADUs.
Owner Occupancy
Owner occupancy is required. The property owner must continuously occupy either the main home or the ADU as their primary residence.
Rental Use
Long-term rentals are generally permitted. Short-term rental restrictions may apply, so check local regulations if you're considering Airbnb or VRBO-style leasing.
How to Build an ADU in Greenwich
Schedule a free consultation with Haven to confirm your eligibility and walk through your options
Work with a Haven designer to develop your custom ADU project that meets Greenwich's local regulations
Haven handles all communication with the municipality and submits your permit application
During construction, the Haven team visits the site regularly to ensure what is being built meets our standards
Certificate of occupancy is issued after the final inspection, allowing the unit to be legally occupied
Permit approval in Greenwich typically takes 4 to 8 weeks on average in Connecticut.
Frequently Asked Questions
Q: 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.
Q: 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.
Q: 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.
Your property must be a single-family residential lot with appropriate zoning designation to be eligible for an ADU in Greenwich. At Haven, we handle the entire ADU process for Greenwich homeowners, from zoning verification and design through permitting and construction. Book a free consultation to find out if your property qualifies.