ADU Rules in Milford, New Hampshire

Milford is a town of approximately 16,000 residents in Hillsborough County in southern New Hampshire, situated on the Souhegan River about 12 miles southwest of Manchester. The town has a well-preserved New England village center and a distinctive industrial heritage rooted in granite quarrying — the local Milford Pink Granite was used in notable structures including the Library of Congress in Washington, D.C. Today, Milford is a residential community with a vibrant downtown and active Town Meeting governance.

New Hampshire RSA 674:71-73 — ADU Rights Statewide

New Hampshire's ADU statute (RSA 674:71-73) requires all New Hampshire municipalities with residential zoning to allow at least one attached ADU by right on any lot containing a single-family dwelling. For Milford property owners:

• An attached ADU must be permitted without a special exception, variance, or conditional use review, provided objective dimensional standards are met
• The town may impose reasonable local standards for setbacks, maximum size, owner occupancy, and parking
• Restrictions cannot be so stringent that they effectively prohibit ADUs in residential zones

Detached ADUs: RSA 674:71 requires attached ADUs by right; the statute allows but does not mandate that municipalities also permit detached ADUs by right. Contact Milford's Planning and Zoning Department to confirm whether Milford's current ordinance permits detached ADUs by right.

ADU Types Permitted

• Attached ADUs (required by state law by right) — basement apartments, in-law suites, first-floor additions, or upper-floor units within or attached to the principal dwelling
• Detached ADUs — freestanding backyard cottages, carriage house conversions, or garage conversions (confirm local rules)
• Garage conversions — converting existing garages into habitable living units
• Interior ADUs — self-contained units created within the primary dwelling's existing floor plan

Size, Setbacks, and Dimensional Standards

Milford's zoning ordinance sets local dimensional standards for ADUs within the framework established by RSA 674:71. Contact the Planning and Zoning Department for current specifics:

• Maximum ADU size: State law prevents municipalities from setting a cap below the greater of 750 sq ft or 30% of the primary dwelling's gross floor area. Milford's specific cap may differ.
• Setbacks: Rear and side yard setback requirements apply for detached ADUs
• Height: Limited to accessory structure height standards of the applicable zone
• Parking: State law limits how many additional off-street spaces may be required
• Owner occupancy: Milford may require the property owner to reside in either the principal dwelling or the ADU

Historic Village Character

Milford's historic village center and adjacent neighborhoods include properties of historical significance. ADU projects on or near historically significant properties should inquire with the Milford Planning Department about any local historic district regulations or design review requirements that may apply to exterior alterations. The Milford Heritage Commission may have advisory input on projects in or near historic areas.

Souhegan River Flood Zone Considerations

The Souhegan River flows through Milford, and portions of the town near the river may be within FEMA-mapped Special Flood Hazard Areas (SFHAs). ADU construction in an SFHA is subject to additional requirements:

• Finished floor elevation must meet or exceed the Base Flood Elevation (BFE)
• A floodplain development permit may be required
• Foundation and fill requirements are more stringent in flood zones

Check flood zone status using the FEMA Flood Map Service Center at msc.fema.gov before planning any ADU near the river.

Permit Process

1. Contact Milford's Planning and Zoning Department to confirm current ADU rules and your parcel's zoning district
2. Confirm FEMA flood zone status if the property is near the Souhegan River
3. Submit a zoning permit application with site plan and floor plans
4. Obtain a building permit under New Hampshire State Building Code requirements
5. Pass all required inspections and receive a certificate of occupancy

Contact Information

Town of Milford Planning and Zoning Department

• Address: 1 Union Square, Milford, NH 03055
• Phone: (603) 249-0600
• Website: milford.nh.gov

Disclaimer: Zoning regulations and state law change frequently. This page is provided for general informational purposes only. Always verify current ADU requirements with the Town of Milford and consult a licensed New Hampshire contractor or architect before beginning any project.