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

Some Restrictions

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

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

Key Facts

County Zoning: One unit per acre
County Review: Additional Dwelling Unit approval
Septic: Health Dept permit off sewer
Fayetteville: Two ADUs, 1,200 sq ft

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 Washington County, AR rules below cover local size, height, and setback requirements.

Summary

In unincorporated Washington County a second home is an Additional Dwelling Unit needing Planning review and a septic permit, since base zoning is one unit per acre. Fayetteville, by contrast, is strongly ADU-friendly.

City-specific rules exist: Springdale has its own adu rules rules that differ from Washington County's county-level regulations. If you live in Springdale, check the city-specific page instead.

A maximum of two (2) accessory dwelling units are permitted provided the combined square footage does not exceed 1,200 square feet. Accessory dwellings may be interior, attached, or detached from the primary dwelling, or attached to each other.

Source: Arkansas CodeView official code

Full Breakdown

Unincorporated Washington County zones every parcel Agricultural/Single-Family Residential, one unit per acre, so a second dwelling is an Additional Dwelling Unit that the Planning office must review even though single-family homes need no building permit. Off public sewer, the Washington County Health Department must issue an individual sewage disposal permit before the unit creates any domestic sewage. Fayetteville is the standout: its Unified Development Code allows up to two accessory dwelling units per lot, up to 1,200 square feet combined, with no added parking required and administrative approval that needs no public hearing, one of the most ADU-friendly ordinances in Arkansas.

Violations & Fines

Adding a second dwelling in the unincorporated county without Planning review, or creating sewage without the Health Department septic permit, triggers enforcement and can force removal or disconnection.

Frequently Asked Questions

Can I build an ADU in Washington County?

In the unincorporated county a second dwelling needs Planning review as an Additional Dwelling Unit plus a septic permit. Fayetteville allows up to two ADUs by administrative approval.

How ADU-friendly is Fayetteville?

Very. Fayetteville's UDC permits up to two accessory dwelling units per lot, up to 1,200 square feet combined, with no additional parking required and no public hearing.

Sources & Official References

[1]Arkansas Code

Other rules in Washington County

Shed & Carport RulesFew Restrictions Garage ConversionsSome Restrictions Tiny HomesSome Restrictions Parking Rules: Abandoned VehiclesSome Restrictions Fence Regulations: Neighbor Fence RulesSome Restrictions Animal Ordinances: Mandatory Spay/NeuterLight Restrictions Animal Ordinances: Exotic PetsSignificant Restrictions Animal Ordinances: Breed RestrictionsSignificant Restrictions Animal Ordinances: BeekeepingFew Restrictions

All Washington County rules

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

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ADU Rules in Cities Across Washington County

Springdale, AR