ADUs are allowed in FranklinTypes:DetachedInternal
Types:DetachedInternal
Accessory Dwelling Unit (ADU) Rules for Franklin, NH
Is your property eligible for an ADU?
# of Properties
3,302
Owner-occupied
64%
Zoning districts
16
Avg Home Value
$283,765
Median Lot Size
0.54 acres
Avg Income
$77,547
Residential Types:
3,302 housing units
Single Family
77%
Apts (4+ units)
9%
Other
14%
Zoning Districts:
3,839 parcels · 16 districts
R-3
17%(652)
R-1
15%(588)
RS
15%(558)
C
13%(514)
Other
40%(1,527)
ADU Rules
What can you build in Franklin, NH?
Franklin, NH follows state and local rules for Accessory Dwelling Units. Here is a concise overview of the local rules.
Eligibility
- –Internal / Attached ADU: By Right
- –Detached ADU: By Right
Interior / Attached ADU Size Limits
- –Maximum size of 750 sq ft for an internal/attached accessory dwelling unit
Detached ADU Size Limits
- –Detached ADUs are not allowed; the maximum permitted size is 0 sq ft.
Max Units
- –Single-family dwelling lot: 1 ADU per lot; Duplex lot: 0 ADUs; Multifamily lot: 0 ADUs; Detached ADU: 0 per lot.
Owner Occupancy
- –Owner must reside in the principal unit or ADU
Parking
- –2 spaces per dwelling unit; no maximum stated; ADU parking must comply with § 305-19; driveway spaces may be within front, side, or rear yard setbacks; tandem stacking permitted for a single unit; for multi-unit buildings, one unit’s parking may not block another unit’s ingress/egress.
ADU State Law
What can you build in New Hampshire?
- –New Hampshire ADU rules after HB 577 (signed July 15, 2025, eff. July 1, 2025 – Chapter 197).
- –One ADU, attached or detached, is allowed By Right on every single-family lot in any zoning district that allows single-family homes.
- –If the local ordinance is silent, the same By Right rule applies. You just need a building permit.
- –Default maximum is 950 sq ft of living space
- –Towns may set a lower maximum, but no lower than 750 sq ft,
- –Town may set a higher maximum
- –If a town specifies a size limit only for Internal or Attached ADUs and is silent on Detached units, we interpret that the state default maximum of 950 sq ft applies to Detached ADUs, since local limits apply only to the types they explicitly regulate.
- –Local zoning rules for ADUs can't be stricter than those for single-family homes, including lot size, frontage, and setbacks.
- –May require up to one additional parking space for each ADU.
- –Owner-occupancy: A town may require the owner to live on the property, but can't say which unit the owner must occupy. No requirement that ADU occupants be related to the main-house occupants.
- –Water & septic: The town can't demand a bigger system than the state DES rules require. Separate systems aren't mandatory, but you must upgrade if the existing one fails or lacks approval.
- –Conversions encouraged: Existing structures (e.g., garages, barns, etc.) may be converted even if they violate current setbacks or lot-coverage limits, and towns can't block a separate electrical panel/service for the ADU.
- –A town may bar ADUs on leased land or on lots with multiple attached single-family dwellings (e.g., townhouses).
What's allowed on your lot?
These are the municipality-wide rules. What's allowed on a specific property also depends on state laws, setbacks, floor area ratio, lot coverage, environmental constraints, topography, and other property-specific factors. Search your address on FutureLot to see what's allowed on your property.
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ADU rules in other New Hampshire municipalities
Rules change at the town line. Check the municipality your property is actually in.
Merrimack County