Introduction

Accessory Dwelling Units (ADUs) are becoming an increasingly popular solution to Connecticut’s housing challenges. While the state has taken steps to encourage ADU development, zoning rules still vary significantly from town to town.

Understanding these differences is critical. Some towns are ADU-friendly with clear pathways to approval, while others impose stricter size limits, parking requirements, or review processes. This guide provides a practical overview of ADU zoning rules in Connecticut and explains what homeowners should review locally before moving forward.

Statewide ADU Rules in Connecticut (What’s Generally Allowed)

Connecticut law encourages municipalities to allow ADUs, but towns retain local control over how they’re implemented.

Across much of the state, ADUs are generally permitted in single-family residential zones, subject to local regulations. However, approval is not automatic, and requirements vary.

Most Connecticut towns address ADUs through their zoning regulations rather than building code alone.

Common ADU Requirements Across Connecticut Towns

While details vary, many towns share similar baseline requirements:

1. ADU Size Limits

Most towns cap ADUs at:

• 600–1,000 square feet, or

• A percentage of the primary home (often 30–40%)

Smaller lots often face tighter limits.

2. Number of ADUs

Typically:

• One ADU per single-family lot

• Some towns allow only internal or attached ADUs

• Others allow detached ADUs with additional review

3. Owner-Occupancy Rules

Many towns require that:

• Either the primary residence or the ADU be owner-occupied

Some towns waive this requirement; others enforce it strictly.

4. Parking Requirements

Common requirements include:

• 1 additional off-street parking space

• More parking for larger ADUs

• Reduced or waived parking near town centers or transit

Parking can be a major approval hurdle on smaller or historic lots.

5. Septic & Utilities

For properties on septic systems:

• Health department approval is required

• Septic capacity must support the additional dwelling

Sewer-connected properties typically face fewer restrictions.

Town-by-Town ADU Zoning Overview (Representative Examples)

Zoning rules change. This section provides general guidance — homeowners should always confirm current regulations with their local zoning office.

Fairfield County (General Trends)

Greenwich, Westport, Darien, New Canaan

• ADUs typically allowed with restrictions

• Detached ADUs often require special permits

• Strict design, size, and parking controls

• Historic districts require additional review

Best suited for:
Attached ADUs, garage conversions, or internal ADUs with careful planning.

Litchfield County

Kent, Roxbury, Washington, Litchfield

• ADUs often permitted but carefully regulated

• Strong emphasis on:

  • Lot size

  • Septic capacity

  • Historic district compatibility

Historic districts may require approval from local commissions.

Best suited for:
Detached ADUs on larger lots, garage apartments, or internal conversions.

New Haven County

Milford, Guilford, Madison

• Generally ADU-friendly with clear zoning language

• Size and parking requirements apply

• Coastal areas may add flood-zone considerations

Best suited for:
Attached or detached ADUs with coastal compliance planning.

Hartford County

West Hartford, Farmington, Avon

• ADUs typically allowed with administrative review

• Clear permitting pathways in many towns

• Parking and owner-occupancy often required

Best suited for:
Internal ADUs and attached additions.

Middlesex County

Essex, Old Saybrook, Chester

• ADUs allowed but subject to village or historic overlays

• Design review may be required

• Coastal flood rules can apply

Historic Districts & ADUs in Connecticut

If your home is located in a local or national historic district, expect additional review:

• Exterior changes often require approval

• Scale, massing, and materials must align with historic character

• Interior ADUs may be easier to approve than detached structures

Historic review does not prevent ADUs—but it does require thoughtful design.

Permits Required for ADUs (Almost Always)

Regardless of town, ADUs typically require:

• Zoning approval

• Building permit

• Electrical, plumbing, and HVAC permits

• Energy code compliance

• Septic or sewer approval (if applicable)

• Final inspections & Certificate of Occupancy

Common Zoning Mistakes Homeowners Make

✗ Assuming ADUs are “by right” everywhere

✗ Designing before confirming zoning feasibility

✗ Ignoring parking and septic constraints

✗ Overlooking owner-occupancy rules

✗ Failing to account for historic or coastal overlays

These mistakes can lead to redesigns, delays, or denials.

How to Approach ADU Zoning the Smart Way

1. Confirm zoning designation of your property

2. Review local ADU regulations (not just state law)

3. Check septic or sewer capacity early

4. Understand parking and access requirements

5. Consult a local builder familiar with your town’s approval process

Conclusion

While Connecticut is moving toward more flexible housing options, ADU zoning rules remain highly town-specific. The key to success is understanding local requirements early and designing within them.

With the right planning and guidance, many Connecticut homeowners can successfully add an ADU that enhances their property, supports family needs, or provides long-term flexibility.

At Casali Companies, we help homeowners evaluate zoning feasibility, navigate town approvals, and design ADUs that meet both regulatory requirements and lifestyle goals.

Not sure if your town allows ADUs?
Contact Casali Companies to review zoning feasibility and explore ADU options for your property.