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Benton County, AR Accessory Structures: ADU Rules (2026)

Some Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified September 2026

ADU rules in Benton County, AR, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

Size cap: 50% of primary dwelling's habitable space
Review track: Exempt from site plan review, §6.1(12)
Applies to: Unincorporated Benton County only
Adopting ordinance: Quorum Court Ordinance No. O-2023-53
Adoption date: August 24, 2023

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Arkansas under recent ADU streamlining laws. The Benton County, AR rules below cover local size, height, and setback requirements.

Summary

Unincorporated Benton County lets property owners build one accessory dwelling unit on a lot with a single-family home, but the ADU cannot exceed 50% of the primary dwelling's habitable floor space. ADUs are exempt from full site plan review under Chapter VI of the county's Planning and Development Regulations.

These county ordinances apply to unincorporated areas of Benton County. Incorporated cities within the county may have their own rules that take precedence over county-level regulations.

ACCESSORY DWELLING UNIT - secondary home on the same lot as a primary dwelling. ADUs are independently habitable and provide the basic requirements of shelter, heating, cooking and sanitation. For the purposes of this ordinance, an ADU shall not exceed 50% of the habitable space of the primary dwelling. 12. ... Accessory Dwelling Units as defined in chapter III.

View official code

Official source re-checked September 7, 2026: the cited page had not changed since it was quoted.

Full Breakdown

Benton County's Planning and Development Regulations define an accessory dwelling unit in Chapter III as a secondary home on the same lot as a primary dwelling that is independently habitable, providing shelter, heating, cooking and sanitation. The definition caps size directly: an ADU cannot exceed 50% of the habitable space of the primary dwelling. That size cap is the operative limit anyone proposing a garage apartment, basement apartment or detached guest house in the unincorporated county has to meet before pulling permits. 1, item 12, alongside one and two family dwellings, agricultural structures, and detached structures under 250 square feet.

2. Building permits are still required through the Planning Division for the structure itself, following the same construction, setback and OSSF/water requirements set out in Chapter IV for any dwelling on the parcel. Property owners in Bentonville, Rogers, Bella Vista, Siloam Springs, Lowell, Centerton, Pea Ridge, Gravette and Gentry are governed by their own city codes, not this county regulation; this rule applies only to unincorporated Benton County land under the Quorum Court's Ordinance No. O-2023-53.

Violations & Fines

An ADU built larger than 50% of the primary dwelling's habitable space does not meet the Chapter III definition the county exemption relies on, which pulls the project into the full site plan review track under §6.2 rather than the exempt path in §6.1. Building without the required permit for the underlying structure exposes the owner to enforcement under the Planning Division's general permit and violations provisions in Chapter II, which apply to any development undertaken without required county approval.

Frequently Asked Questions

How big can an ADU be in unincorporated Benton County?

The ADU cannot exceed 50% of the habitable floor space of the primary dwelling on the lot, per the Chapter III definition in the Planning and Development Regulations. That percentage is the controlling limit for garage apartments, basement units and detached guest houses alike.

Does an ADU need site plan review in Benton County?

No. Chapter VI, §6.1, item 12 lists accessory dwelling units among the developments exempted from site plan review, so an ADU that meets the Chapter III size definition skips that separate review track required for larger commercial and residential projects.

Does this ADU rule apply inside Bentonville or Rogers?

No. This regulation governs unincorporated Benton County land only. Bentonville, Rogers, Bella Vista, Siloam Springs and the county's other incorporated cities each zone under their own municipal code, not the county's Planning and Development Regulations.

Sources & Official References

[1]Benton County Planning and Development Regulations (2023 Effective)

Other rules in Benton County

Fence Regulations: Height LimitsSome Restrictions Shed & Carport RulesSome Restrictions Noise Ordinances: Amplified Music & Outdoor SoundSome Restrictions Noise Ordinances: Decibel LimitsSome Restrictions Parking Rules: Loading ZonesSome Restrictions Parking Rules: Abandoned VehiclesSignificant Restrictions Fence Regulations: Fence Permit RequirementsSome Restrictions

All Benton County rules

How Benton County compares: Easiest Cities to Build an ADU·Compare Benton County to another location·View the Arkansas accessory structures overview

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