Dorchester County ADU Rules 2026: 800-Sq-Ft Cap, Owner Occupancy, Parking & HB 1466 Conflict

Dorchester County still publishes a legacy accessory-apartment framework that does not cleanly match Maryland’s 2025 ADU law. The current County code limits an accessory apartment to space within an owner-occupied single-family detached dwelling and caps it at the lesser of 800 square feet or one-third of the building. Maryland’s HB 1466 framework requires local governments to authorize qualifying ADUs up to 75% of the primary dwelling’s size and contemplates attached and detached units as well.

The safest way to plan in Dorchester County right now is to distinguish the current codified accessory-apartment rules from Maryland’s newer statewide ADU requirements. The County code has recent 2026 zoning amendments listed, but the live codified definition of accessory apartment still shows the older 800-square-foot/one-third framework. Until the County publishes a clearly compliant replacement ADU rule, homeowners should confirm the controlling standard directly with Dorchester County Planning & Zoning before paying for final design.

Last verified: September 13, 2026. Dorchester County’s eCode lists zoning amendments adopted March 17 and August 4, 2026, but the live accessory-apartment definition and parking table still display the legacy standards discussed below. This page does not assume an uncodified change unless supported by a primary source.

Dorchester County ADU status at a glance

What Dorchester County’s current accessory-apartment rule says

Dorchester County’s live zoning definition describes an accessory apartment as a second dwelling unit located within an owner-occupied single-family detached dwelling. It may occupy no more than 800 square feet or one-third of the total area of the building, whichever is less.

The same definition requires the property owner to occupy either the principal dwelling or the accessory apartment. That makes Dorchester’s currently codified framework much narrower than the modern statewide ADU concept, which can include attached additions and separate detached structures.

Why the 800-sq-ft / one-third rule creates a 2026 conflict

Maryland Department of Planning’s HB 1466 FAQ says local jurisdictions must authorize ADUs consistent with the state definition and may not limit qualifying ADUs below 75% of the size of the primary single-family detached dwelling. The Department recommends finished living area above grade as a measurement method where local law does not specify otherwise.

Dorchester’s live code still uses a much lower ceiling: the lesser of 800 square feet or one-third of the building. It also defines the accessory apartment as being inside the principal house. For that reason, we do not treat Dorchester’s current code as a clearly final HB 1466-compliant framework.

What is the current parking rule?

Dorchester County’s parking table requires one parking space per accessory apartment. Section 155-56 also states that parking for accessory uses is provided in addition to the parking required for the principal use.

Maryland HB 1466 says a local government may not impose additional ADU parking requirements unless it first completes a parking study, and any local law requiring additional ADU parking must provide a waiver process. Dorchester’s general parking chapter does allow the Planning Commission to approve deviations through site-plan review, but that is not necessarily the same thing as an ADU-specific HB 1466 waiver process. Homeowners should therefore confirm the County’s current implementation before assuming one additional space is automatically required.

What setbacks apply to a detached structure?

The current County code says that, unless another provision applies, accessory structures may be placed in required side or rear yards but must generally remain at least 6 feet from side and rear lot lines. If an accessory structure is physically attached to the principal structure, it becomes part of that principal structure for setback purposes.

Maryland HB 1466 also says side and rear ADU setbacks may not be more restrictive than the setbacks already applicable to accessory structures. This becomes important if Dorchester expands its ordinance to expressly authorize detached ADUs.

Septic, well, Critical Area and floodplain review can decide feasibility

Dorchester County Health Department reviews building and use-and-occupancy permits for properties served by private wells or septic systems. It conducts perc tests, reviews septic plans, issues septic permits and reviews well placement. On a rural property, that review can be just as important as the zoning rule because an additional dwelling unit can increase wastewater and water-supply demands.

Floodplain and Chesapeake Bay Critical Area rules also matter in Dorchester County. The zoning code contains separate floodplain standards for accessory structures, including elevation and flood-damage requirements in mapped hazard areas. A parcel can therefore satisfy a basic ADU rule and still face substantial siting or construction constraints.

Use our Maryland ADU Septic & Well Guide before committing to plans on a property without public utilities.

Cambridge and other towns can follow a different zoning path

Do not assume Dorchester County zoning controls every Dorchester mailing address. The City of Cambridge maintains its own Planning & Zoning Department and Unified Development Code. Cambridge materials specifically reference accessory dwelling units and a separate local licensing/approval framework.

Dorchester County’s own permit checklist also tells applicants in Brookview, Church Creek, East New Market, Eldorado, Galestown and Vienna to provide town permit paperwork when applicable. Use the Maryland ADU Jurisdiction Finder before relying on County rules.

What Dorchester homeowners should verify before spending money

1. Confirm the zoning authority. Determine whether County zoning or a municipality controls the parcel.
2. Ask which 2026 ADU standard is being applied. The live code still shows the older accessory-apartment definition.
3. Confirm the size measurement in writing. Do not assume the old 800-square-foot cap or a 75% maximum without County confirmation.
4. Ask whether detached ADUs are currently accepted. The codified accessory-apartment definition is interior-only.
5. Confirm parking. Ask whether the one-space requirement remains applicable and what waiver process, if any, satisfies HB 1466.
6. Check accessory-structure setbacks and overlays. Floodplain and Critical Area rules can alter the buildable envelope.
7. Check septic and well capacity early. The Health Department reviews permits on private systems.
8. Re-check before final design or a prefab deposit. Dorchester’s rules are still in a regulatory transition period.

Primary sources used for this Dorchester County guide

• Dorchester County Code § 155-13 — Accessory Apartment definition
• Dorchester County Code Article XI — Parking and Loading
• Dorchester County Code § 155-50 — Accessory uses and structures
• Maryland Department of Planning — HB 1466 ADU FAQ
• Dorchester County Health Department — Perc Tests and Septic Systems
• Dorchester County Health Department — Wells and Individual Water Supply
• City of Cambridge — Planning & Zoning

For statewide comparison, use the Maryland County ADU Rules Tracker. Maryland ADU Guide is maintained by Gijo John as an independent research publication. Verify property-specific requirements with the controlling local agency before relying on this page for design, permitting or construction decisions.