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

Significant Restrictions

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

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

Key Facts

Permit required: Certificate of Compliance (Shoreland Overlay)
Units allowed: One accessory apartment per dwelling
Renewal: Annually each January, with affidavit
Separate curb cut: Prohibited
Governing provision: Development Code Ch. 2, Sec. 2.1

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 Minnesota under recent ADU streamlining laws. The Washington County, MN rules below cover local size, height, and setback requirements.

Summary

An accessory apartment in unincorporated Washington County needs a Certificate of Compliance in the Shoreland Management Overlay District, is capped at one per single-family dwelling, and the underlying home must be owner-occupied under Development Code Section 2.1.

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

Accessory Apartments
(1) Required Permit: Accessory Apartments are permitted within the Shoreland Management Overlay District with a Certificate of Compliance, provided that local ordinance allows Accessory Apartments within the underlying zoning district. (3)(A) More than one accessory apartment within a single family dwelling unit is prohibited. (3)(C) A separate curb cut for the accessory apartment unit is prohibited.

View official code

Full Breakdown

1 of the Development Code, titled Accessory Apartments, defines the use as 'a secondary dwelling unit within an existing owner-occupied single family dwelling for the use as a complete independent living facility,' and notes that no density unit is attributed to it when calculating lot density. 1(2) requires compliance with all federal, state, county and local rules. 1(3)(D)). This provision is limited to single-family homes in agricultural and residential districts within the unincorporated county and does not apply inside cities like Stillwater or Woodbury, which set their own accessory-dwelling standards.

Violations & Fines

Operating an accessory apartment without the required Certificate of Compliance, adding a second unit beyond the one-per-dwelling cap, or failing the annual January renewal and supporting affidavit puts the Certificate of Compliance at risk of revocation by the Zoning Administrator, and an apartment found out of compliance can be ordered brought into conformance or discontinued.

Frequently Asked Questions

Do I need a permit for an accessory apartment in Washington County?

Yes, in the Shoreland Management Overlay District a Certificate of Compliance is required under Section 2.1(1), and it must be renewed every January under Section 2.1(3)(D) with an affidavit confirming the circumstances have not changed.

How many accessory apartments can one home have?

Just one. Section 2.1(3)(A) states that more than one accessory apartment within a single family dwelling unit is prohibited.

Can I build a separate driveway for the accessory apartment?

No. Section 2.1(3)(C) prohibits a separate curb cut for the accessory apartment unit, so it must share the existing driveway access with the main house.

Sources & Official References

[1]Washington County Development Code, Chapter Two: Zoning Regulations

Other rules in Washington County

Shed & Carport RulesSome Restrictions ADU Owner OccupancySignificant Restrictions Garage ConversionsHeavy Restrictions Noise Ordinances: Amplified Music & Outdoor SoundSome Restrictions Parking Rules: Abandoned VehiclesSome Restrictions Parking Rules: Commercial & Oversized VehiclesSignificant Restrictions Parking Rules: Driveway RulesSome Restrictions Fence Regulations: Fence Permit RequirementsSome Restrictions Fence Regulations: Neighbor Fence RulesLight Restrictions

All Washington County rules

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

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