ADUs are allowed in CarrollTypes:DetachedInternal
Types:DetachedInternal
Accessory Dwelling Unit (ADU) Rules for Carroll, NH
Is your property eligible for an ADU?
# of Properties
1,569
Owner-occupied
5%
Zoning districts
7
Avg Home Value
$300,931
Median Lot Size
3.24 acres
Avg Income
$81,302
Residential Types:
1,569 housing units
Single Family
63%
Apts (4+ units)
1%
Other
36%
Zoning Districts:
1,769 parcels · 7 districts
Resid - Bretton Wds
37%(655)
Resid - Business
26%(464)
Rural
24%(428)
Resid - Twin Mtn
12%(206)
Other
1%(16)
ADU Rules
What can you build in Carroll, NH?
Carroll, 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 is the greater of 750 sq ft or 30% of the single-family dwelling’s total floor area (including the ADU).
Detached ADU Size Limits
- –Maximum ADU size is the larger of 750 sq ft or 30% of total floor area (interpreted as 3/7 of the primary dwelling’s floor area).
Max Units
- –1 ADU per single-family dwelling
Owner Occupancy
- –No owner-occupancy requirement.
Parking
- –1 space/ADU, in addition to 2 for the principal dwelling; no stated waivers/reductions
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.
Coos County