Washington County has an enacted ADU ordinance, and it is one of Maryland’s clearer county frameworks. Ordinance ORD-2025-33 took effect October 14, 2025 and allows one accessory dwelling unit on qualifying properties in a wide range of rural and urban zoning districts. The main homeowner checks are the 75% size rule, the separate 1,200-square-foot cap, parking, setbacks, and whether the property is inside Hagerstown rather than under County zoning.
The safest way to plan is to first confirm whether the parcel is governed by Washington County or a municipality. County Ordinance ORD-2025-33 applies to County zoning. The City of Hagerstown has its own land-management code and is separately considering 2026 ADU amendments, so a Hagerstown address should not automatically be evaluated under the County ordinance.
Enacted local framework · Last verified September 13, 2026
🟢 Active — ORD-2025-33 was adopted and effective October 14, 2025.
The ordinance allows one ADU per qualifying lot, permits attached and detached forms, uses a 75% size basis, and applies accessory-structure setbacks. A separate 1,200-square-foot absolute cap should still be checked against Maryland’s HB 1466 guidance on properties where 75% of the principal dwelling would exceed 1,200 square feet.
Last verified: September 13, 2026. Washington County’s official ordinance record and local legal-materials index were reviewed together with Maryland Department of Planning’s HB 1466 FAQ. This page is informational and is not legal, zoning, architectural, engineering or permitting advice.
Washington County ADU status at a glance
| Question | Verified status |
|---|---|
| Are ADUs allowed? | Yes. ORD-2025-33 permits ADUs by right in specified County zoning districts. |
| Effective date | October 14, 2025. |
| Allowed forms | Within a single-family detached dwelling, in an addition, or in a detached accessory unit or structure. |
| How many? | Generally one ADU per lot, with special rules for duplex and commercial-zone lots. |
| Maximum size | Lesser of 75% of the primary dwelling’s gross floor area or 1,200 sq ft. The 1,200-sq-ft absolute cap is a state-law clarification point on larger homes. |
| Parking | One additional space; lawful on-street parking may satisfy it. The requirement is waived within ½ mile of a transit stop. |
| Setbacks | ADUs generally follow accessory-structure setback, height and lot-coverage standards unless the ADU rule modifies them. |
| Owner occupancy | No owner-occupancy requirement was identified in ORD-2025-33’s ADU standards. |
| Hagerstown | Separate city zoning applies. Do not use County rules automatically for parcels inside Hagerstown. |
How big can a Washington County ADU be?
The ordinance says an ADU may be no more than 75% of the gross floor area of the primary dwelling or 1,200 square feet, whichever is less. If a basement or attic is used for an attached ADU, the ordinance allows the ADU area to equal the area of that basement or attic.
The 75% language tracks Maryland’s statewide ADU definition. The separate 1,200-square-foot cap deserves caution, however. Maryland Department of Planning says jurisdictions may not limit qualifying ADUs below the 75% limit. On a large primary dwelling, a 1,200-square-foot ceiling could produce a lower maximum than 75%, so confirm how the County is administering that provision before designing to the limit.
What is the parking rule?
Washington County requires one parking space for the ADU in addition to parking required for the principal dwelling. Lawful on-street parking may count toward this requirement.
The ordinance also contains a clear transit exemption: the additional-space requirement is waived for any lot within one-half mile of a transit stop. Maryland’s HB 1466 framework requires a parking study when a jurisdiction imposes additional ADU parking and requires a waiver process. Washington County’s transit waiver is therefore an important part of the local rule, but property owners outside that radius should still verify whether any additional administrative waiver path exists for their site.
How do setbacks work?
Unless specifically modified by the ADU section, the unit must comply with the setback, height and building-lot-coverage standards for accessory structures in the underlying zoning district. This is important because Maryland’s state framework generally limits local side and rear ADU setbacks to those otherwise applicable to accessory structures.
The actual buildable envelope can still be affected by easements, floodplain, utility areas, septic reserve areas and other parcel-specific constraints.
Does Washington County require owner occupancy?
I did not identify an owner-occupancy requirement in the enacted ADU standards of ORD-2025-33. That is different from several Maryland counties that still tie ADU eligibility to an owner living in the principal dwelling or the ADU.
That does not mean every rental arrangement is automatically permitted. Rental licensing, short-term-rental rules, private covenants and other laws can still apply separately.
Septic and well capacity can still decide feasibility
Washington County’s residential permit materials direct properties using private water or wastewater systems to the Washington County Health Department for well and septic permits. The County checklist requires applicants to coordinate the dwelling location, sewage-disposal area and well location with Environmental Health.
If a parcel is not served by public water and sewer, treat septic and well review as an early feasibility step rather than something to resolve after design. A property can meet the zoning rules and still fail because the existing sewage-disposal area, reserve area or water-supply configuration cannot support the additional dwelling.
Hagerstown is a separate ADU jurisdiction
The City of Hagerstown administers its own zoning. In 2026 the City published a proposed Land Management Code amendment that would add a dedicated ADU section using a 75% size standard and accessory-structure setback rules.
Because that is a City process, it should not be mixed with Washington County’s enacted ORD-2025-33. If the parcel is inside Hagerstown, verify the current City code and the status of its 2026 amendment before relying on the County guide.
What Washington County homeowners should do now
- Confirm jurisdiction. Determine whether the parcel is under County zoning or inside Hagerstown or another municipality.
- Confirm the zoning district. ORD-2025-33 permits ADUs only in the districts listed in the ordinance.
- Calculate both size limits. Compare 75% of the primary dwelling’s GFA with 1,200 sq ft and ask the County how it is administering the hard cap.
- Check parking early. Determine whether lawful on-street parking can be counted or whether the half-mile transit waiver applies.
- Map accessory setbacks. Use the underlying district’s accessory-structure standards for detached-unit feasibility.
- Check well and septic capacity before final design. Health Department review may control the project on non-public systems.
- Verify rental rules separately. ADU zoning approval does not automatically answer long-term rental, STR, licensing or HOA questions.
Primary sources used for this Washington County guide
- Washington County ORD-2025-33 — Accessory Dwelling Units
- Washington County — Local Legal Materials
- Washington County — Resolutions & Ordinances
- Washington County — Residential Permit Application Checklist
- Maryland Department of Planning — HB 1466 ADU FAQ
- City of Hagerstown — 2026 Land Management Code amendment proposals
For statewide comparison, use the Maryland County ADU Rules Tracker. Maryland ADU Guide is maintained as an independent research publication; verify property-specific requirements with the controlling local agency before relying on this guide for design or construction decisions.
What to do next
Start by finding the office that reviews your property. A mailing city or a county guide does not establish your parcel’s authority.
- Find Who Reviews My Property.
- Obtain your parcel identifier, survey, floor plans and utility records.
- Ask the reviewing office which current rules, supporting documents and approvals apply.
- Continue to your planning workspace.
Enable JavaScript to prepare a downloadable next-step brief. Planning guidance is not permit approval.