Baltimore County ADU Rules 2026: Permits, Size & HB 1466 Transition

Yes—Baltimore County currently allows qualifying accessory apartments under its published legacy zoning framework. Interior units follow a Use Permit path; detached units require a Special Hearing plus a Use Permit. Because the County Council’s adopted and pending 2026 legislation lists do not yet show an ADU conformity bill, treat the older dimensional limits as the current published framework—not a promise of the final post-HB 1466 rules. Confirm the permit route and measurements with the County before paying for plans. See the Maryland ADU Rules Tracker for research coverage and the Maryland ADU Guide for statewide context.

Research record: Core framework independently rechecked September 20, 2026. Status: Legacy framework / Transition. Limited legislative-title check: October 21, 2026 (UTC). The County Council’s adopted list includes bills through 97-26, and its pending list includes bills 98–119, introduced October 5 and October 19. No measure specifically titled as an ADU, accessory-apartment or HB 1466 conformity bill was identified. This limited check does not establish the absence of other changes or determine County compliance. Current code and application requirements were not independently revalidated in this update; confirm current administration directly with Permits, Approvals and Inspections. This guide is informational and is not legal, zoning, architectural, engineering or permitting advice.

Baltimore County ADU status at a glance

The accessory-apartment framework documented in our earlier review

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.

Earlier published 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.

Earlier published 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.

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. Use our Maryland 75% ADU Size Calculator & Measurement Guide to compare the statewide planning method with counties where a local measurement basis is verified.

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.

On September 11, we checked the Council’s 2026 adopted-legislation list and pending-legislation list, including the September 8 introductions. Their listed titles did not identify an ADU or accessory-apartment conformity bill. This limited list check does not prove that no relevant measure exists or determine legal compliance. The published legacy framework is verified from the zoning materials reviewed; the unresolved issue is Baltimore County’s final HB 1466 conformity framework. No new post-HB-1466 size, setback or parking result is enabled by this review.

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

1. Confirm whether the project is interior/attached or detached. The current approval path differs materially.
2. Check the current County code and Council legislation again. The October 1, 2026 state deadline has passed; confirm the currently administered rules and any effective amendments before finalizing your plans.
3. 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.
4. Check accessory-building geometry for detached projects. Rear-yard placement, coverage, setbacks and height can affect feasibility before construction cost matters.
5. Verify utilities and private septic/well conditions. Use our Maryland Septic & Well Readiness Checker if the property is not on public utilities.
6. Estimate the budget only after feasibility. First review our Maryland ADU Cost Escalation Guide to identify site, utility, permitting and scope items that may sit outside a headline quote, then use the Maryland ADU Cost & Bid Tool to build the actual project budget and compare written contractor scope.
7. Re-check immediately before signing a contract or prefab deposit. A pending county law can change dimensions, procedure or documentation.

What does BCZR mean, and which records should you gather?

BCZR means Baltimore County Zoning Regulations. It is the zoning rulebook referenced in the county’s 2023 Zoning Policy Manual. A citation such as §400.4 points to a section of that rulebook; it is not an application number or evidence that a property has approval.

For the accessory-apartment provisions discussed in this guide, start with the county zoning code’s Section 400. Read the definition, the applicable provision and any cross-references together. Ask the reviewing office which current text and amendments apply to your proposal. This explanation does not establish that the earlier framework has completed its 2026 transition.

A preparation folder for your first county inquiry

Added September 14, 2026. The county application PDF returned an access error during this check. The following is our suggested preparation list, not a newly verified county submission checklist.

• Property identity: address, parcel identifier and zoning classification. Use the Jurisdiction Finder to check the authority before relying on a mailing address.
• Existing records: available survey or plat, floor plans, building permits and any previous zoning or hearing decisions affecting the property.
• Proposed arrangement: describe whether the unit is inside the house, part of an addition or in a detached building. Include proposed floor area and an initial location sketch.
• Occupancy and services: note the proposed occupants, owner occupancy, intended rental use and how water, sewer, electricity or private systems would serve the unit.
• Questions for the county: request the current application form, permit or hearing route, required plans, fees, and instructions for any declaration or recording process.

Ask for the current application requirements

I am considering an accessory apartment at [address and parcel identifier], configured as [interior, attached or detached]. Please identify the applicable BCZR provisions and any effective amendments, confirm the approval route, and provide the current application checklist. Please explain any Declaration of Understanding, property-description or Land Records requirements, including the correct sequence and documents to submit back to your office. Please also confirm the size, occupancy and utility rules applicable to this proposal.

The county application and declaration guide is the existing source linked by this article. If that file does not open, request a current copy from Permits, Approvals and Inspections rather than treating an old sample as a completed filing. Save the dated response with your project records. For a property in Baltimore City, use the separate Baltimore City guide.

Primary sources used for this guide

• Baltimore County Zoning Regulations §400.4 — Accessory Apartments
• Baltimore County Zoning Regulations §101.1 — Accessory Apartment definition
• Baltimore County — Accessory Apartment Application and Declaration of Understanding Guide
• Baltimore County Bill 7-23 — Accessory Apartments
• Baltimore County Council — 2026 Legislation
• Maryland Department of Planning — HB 1466 ADU FAQ
• Maryland General Assembly — HB 1466 / Chapter 197

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