Baltimore County ADU Rules 2026: Current Code & HB 1466

Baltimore County still publishes an older “accessory apartment” framework while Maryland’s 2025 ADU law requires a new local law by October 1, 2026. That means homeowners need to separate what the County’s current zoning code says today from what must change when Baltimore County aligns with HB 1466.

Last verified: September 6, 2026. This guide is informational and is not legal, zoning, architectural, engineering or permitting advice.

Baltimore County ADU status at a glance

Question	Verified answer
Does Baltimore County currently have an ADU framework?	Yes, but it is a legacy accessory-apartment framework. Current BCZR §400.4 remains published in Municode.
Interior / attached conversion	Use Permit process. Current cap: the lesser of one-third of the dwelling’s overall floor area or 2,000 sq ft.
Detached accessory building	Special Hearing + Use Permit. Current cap: 1,200 sq ft on a lot of at least one acre; 800 sq ft on a smaller lot.
Owner occupancy	Yes under the current definition: the property must be owner-occupied, and the owner may live in either unit.
Who may occupy the accessory apartment?	The current definition still requires occupants of the two units to be family related by blood, marriage or adoption.
Can rent be charged?	Bill 7-23 removed the prior prohibition on compensation, so the current code no longer requires the accessory apartment to be provided without compensation.
Permit renewal	The Use Permit is renewed every two years under the current framework.
Is this already aligned with HB 1466?	No final conforming Baltimore County ADU ordinance was found in the County Council’s published 2026 legislation through this review. Maryland requires a compliant local law by October 1, 2026.

Why we call Baltimore County’s current system a legacy framework

Baltimore County’s current zoning regulations use the term accessory apartment. The definition covers second living quarters within a principal single-family detached dwelling or within an accessory building on the same lot, with dedicated bathing and cooking facilities. The property must be owner-occupied.

Bill 7-23, effective April 22, 2023, broadened the family rule from the older immediate-family formulation to family related by blood, marriage or adoption and removed the rule that the apartment had to be provided without compensation. It did not replace the overall accessory-apartment structure with Maryland’s new 75% ADU framework.

Current path for an interior or attached accessory apartment

Approval: Apply to Permits, Approvals and Inspections for a Use Permit.
Size: No more than one-third of the dwelling’s overall floor area or 2,000 sq ft, whichever is less.
Use: Improvements dedicated to the apartment are to be used as a single-family residence.
Utilities: The current code says the accessory apartment may not have separate utility meters such as gas and electric service.
Recorded document: Baltimore County’s application guide requires a Declaration of Understanding and property description to be recorded in Land Records before the Use Permit is completed.
Renewal: The Use Permit is renewed every two years.

Baltimore County’s zoning policy manual also treats a proposed addition to an existing single-family detached dwelling as part of the interior/attached Use Permit path rather than automatically requiring the detached-unit Special Hearing path, although other variances or approvals may still be needed.

Current path for a detached accessory apartment

Approval: Request a Special Hearing and a Use Permit; a public hearing before the Office of Administrative Hearings is required.
Size: Up to 1,200 sq ft on a lot of at least one acre; up to 800 sq ft on a lot smaller than one acre.
Accessory-building rules: Section 400 requirements still apply, including location, lot-coverage, setback and height rules for accessory buildings.
Utilities: Separate utility meters or water/sewer services are generally not allowed unless the Office of Administrative Hearings approves them based on specific findings of necessity.
Conditions: The hearing officer may impose conditions needed to protect surrounding properties.

Do not confuse permission with buildability. A detached accessory apartment can still be constrained by accessory-building placement, lot coverage, setbacks, height, utilities, septic/well capacity and other property-specific requirements.

What happens when the property is sold or occupancy changes?

Under the current §400.4 framework, if the accessory apartment is no longer occupied by a person named in the Use Permit or the property is sold, the Use Permit terminates and a new request is required for the proposed occupancy. This is another reason we treat the existing system as a legacy framework rather than assume it will survive unchanged after HB 1466 implementation.

Where the current Baltimore County rules differ from Maryland HB 1466

Maryland HB 1466 became effective October 1, 2025 and requires covered counties and municipalities to adopt a local ADU law by October 1, 2026. Maryland Planning says the local law must authorize ADUs consistent with the state definition: an ADU may be up to 75% of the size of the primary single-family detached dwelling.

Maryland Planning’s official FAQ is unusually clear on size: jurisdictions may not set a maximum below that 75% state definition. Baltimore County’s existing one-third interior cap and fixed 800/1,200 sq ft detached caps therefore cannot simply be assumed to be the final post-HB-1466 size rules.

The new state framework also says a conforming local law may not impose side or rear setbacks more restrictive than the jurisdiction’s existing accessory-structure setbacks. If a locality imposes additional ADU parking requirements, it must first complete a parking study and must provide a waiver process. HB 1466 does not require every ADU to be approved by right; a local government may still use a conditional-use or special-exception process.

As of this September 6 review, the Baltimore County Council’s published 2026 legislation list and the then-current pending-legislation page did not show an accessory-dwelling-unit or accessory-apartment conformity bill. That can change quickly as the October 1 deadline approaches, so this page will remain marked Legacy / transition until a final local law is verified.

Parking: what can we safely say today?

BCZR §400.4 does not itself state a specific new ADU parking-space number. That does not mean every property is free of parking or access constraints; general zoning, site-plan, driveway or hearing conditions may still matter. For the post-HB-1466 ordinance, any additional ADU parking requirement will have to comply with Maryland’s parking-study and waiver rules.

What a Baltimore County homeowner should do before spending money

Confirm whether the project is interior/attached or detached. The current approval path differs materially.
Check the current County code and Council legislation again. The October 1, 2026 state deadline is close.
Do not design only to the old size caps. They are part of the current legacy framework but Maryland’s 75% rule requires local alignment.
Check accessory-building geometry for detached projects. Rear-yard placement, coverage, setbacks and height can affect feasibility before construction cost matters.
Verify utilities and private septic/well conditions. Use our Maryland Septic & Well Readiness Checker if the property is not on public utilities.
Estimate the budget only after feasibility. Use the Maryland ADU Cost & Bid Tool and compare written contractor scope, not only total price.
Re-check immediately before signing a contract or prefab deposit. A pending county law can change dimensions, procedure or documentation.

Primary sources used for this guide

Maryland ADU Guide is an independent research publication maintained by Gijo John. Source-backed corrections can be sent to gijo.j@marylandaduguide.com.