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

Heavy Restrictions

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

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

Key Facts

Governing section: Zoning Ordinance § 4.10(b)(1)
Default rule: Accessory structures cannot be living quarters
RT District exception: Guest house allowed as accessory use, § 7A.3(c)
Rural districts: Guest house needs Special Exception (Table 3.3(1))
Not allowed: Rural Business, Industrial Mineral districts (N)
Setback rule: Accessory structure meets principal dwelling side yard, § 4.10(b)(5)

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

Summary

Washington County, Maryland's Zoning Ordinance flatly bars turning a garage, shed or other accessory building into living quarters. Section 4.10(b)(1) makes it unlawful countywide unless the Ordinance specifically authorizes an exception, such as a guest house approved through the Residential, Transition District or a special exception in a rural district.

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.

In addition to the other requirements of this Ordinance, an accessory use shall not be permitted unless it strictly complies with the following: 1. No accessory structure shall be used for living quarters, the storage of contractors' equipment, the storage of animals, or the conducting of any business unless otherwise provided in this Ordinance.

View official code

Full Breakdown

10 of the Washington County Zoning Ordinance governs "Accessory Structures and Uses" everywhere outside the incorporated towns of Hagerstown, Boonsboro, Williamsport, Smithsburg, Funkstown and Hancock, which run their own codes. " A homeowner cannot simply wire and plumb a detached garage or pool house as a rental unit, in-law suite or garage apartment; that use is prohibited by default. 10(b)(2) adds that no accessory structure may even be built before the principal structure is substantially complete, and (b)(5) requires accessory structures to meet the same side-yard setback as the principal dwelling in districts allowing single-family or two-family homes.

The Ordinance does carve out narrow exceptions rather than a blanket ban. 3(c) lists a "Guest house in an accessory building" as a permitted accessory use alongside swimming pools and private stables. In the rural zoning districts, Table No. 3 lists the same use, "Guest house in an accessory building," as a Special Exception (SE) requiring Board of Zoning Appeals authorization after a public hearing in the Agriculture (Rural), Environmental Conservation, Preservation and Rural Village districts, and it is not allowed (N) at all in Rural Business or Industrial Mineral districts. 10(b)(1). 10 remains in force as written.

Violations & Fines

Occupying or converting an accessory structure as living quarters without an authorized guest-house special exception or RT-district approval is a zoning violation enforced by the Washington County Division of Plan Review and Permitting / Zoning Administrator. Because the use itself is prohibited under Section 4.10(b)(1) rather than merely unpermitted construction, the remedy is removal of the illegal use or occupancy, and the property owner has no right to convert the space until a Special Exception is granted by the Board of Zoning Appeals where the district table allows it.

Frequently Asked Questions

Can I turn my detached garage into an apartment in Washington County, Maryland?

No, not by default. Section 4.10(b)(1) of the Zoning Ordinance prohibits using any accessory structure for living quarters unless the Ordinance specifically provides otherwise, such as an approved guest house in a district that allows it.

Is a guest house ever allowed in an accessory building here?

Yes, but only where the land use table permits it. Section 7A.3(c) allows it as an accessory use in the RT Residential, Transition District, while Table No. 3.3(1) requires a Special Exception from the Board of Zoning Appeals in most rural districts and bans it outright in Rural Business and Industrial Mineral districts.

Does this rule apply inside Hagerstown or Boonsboro?

No. Hagerstown, Boonsboro, Williamsport, Smithsburg, Funkstown and Hancock are incorporated towns that administer their own zoning codes; Section 4.10 governs unincorporated Washington County and any area under the county's zoning jurisdiction.

Sources & Official References

[1]Washington County, MD Zoning Ordinance (Section 4.10)

Other rules in Washington County

Parking Rules: Street Parking LimitsSome Restrictions Shed & Carport RulesSome Restrictions Parking Rules: RV & Boat ParkingSome Restrictions Parking Rules: Commercial & Oversized VehiclesSignificant Restrictions Parking Rules: Loading ZonesLight Restrictions Parking Rules: Abandoned VehiclesSome Restrictions Fence Regulations: Retaining WallsSome Restrictions

All Washington County rules

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

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