Maryland ADU Deadline: What Happens If Your County Isn’t Ready by October 1, 2026?

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Maryland’s October 1, 2026 ADU deadline is a legal deadline for local legislative bodies—not an automatic statewide permit switch. HB 1466 requires each covered legislative body to adopt a local law authorizing accessory dwelling units in accordance with Maryland Land Use §4-504 by that date. But the statute does not say that every inconsistent local zoning provision disappears on October 2, and it does not create an automatic-approval process for homeowners whose jurisdiction has not finished its update.

Deadline watch

October 1, 2026

Local legislative bodies must adopt an ADU law that complies with the requirements of Maryland Land Use §4-504. Last editorial verification: September 7, 2026.

This guide focuses on the narrow question homeowners are likely to face during Maryland’s 2026 transition: what should you do if your county or municipality has not finished aligning its ADU rules by the state deadline? For the current jurisdiction-by-jurisdiction picture, use our Maryland County ADU Rules Tracker.

This is an independent primary-source research guide, not legal advice. Where state and local materials do not provide a clear answer, we label the issue unresolved rather than infer a legal remedy.

1. What HB 1466 actually requires by October 1

Maryland enacted HB 1466 as Chapter 197 in 2025. The act became effective October 1, 2025, with a separate implementation deadline one year later. Maryland Land Use §4-504(a)(1) now states that on or before October 1, 2026, each legislative body shall adopt a local law authorizing the development of accessory dwelling units in accordance with that section.

The Maryland Department of Planning summarizes the same timeline in its HB 1466 FAQ: the law took effect October 1, 2025, and local governments must adopt their local ADU laws by October 1, 2026.

The state framework also sets several important boundaries for those local laws. Among them:

  • ADU definition: the secondary dwelling may be no greater than 75% of the size of the primary single-family detached dwelling. The statute does not itself define the measurement method.
  • Density and growth limits: the local law must exclude the ADU from density calculations and from measures limiting residential growth on the affected property.
  • Side and rear setbacks: the local law may not establish ADU side/rear setbacks that exceed the jurisdiction’s existing accessory-structure setback requirements.
  • Parking: if a jurisdiction wants additional off-street parking requirements for ADUs, it must first complete a parking study, consider specified factors, and provide a waiver process.
  • Health and safety: local laws may still require compliance with relevant building codes, adequate-public-facilities provisions, and other public health, safety and welfare standards.
Important distinction: HB 1466 establishes requirements for the local law that must be adopted. It does not turn Maryland into a single statewide ADU zoning code with one uniform local permitting process.

For the full statewide baseline, see our Maryland ADU Guide 2026. If you are specifically testing the 75% size concept, use our Maryland ADU Size Calculator & Measurement Guide, which distinguishes verified local methods from state-guidance estimates.

2. What happens on October 2 if a jurisdiction is not ready?

This is where the statute becomes much less explicit.

Land Use §4-504 clearly creates the October 1 adoption deadline. But HB 1466 does not contain language saying that, at 12:01 a.m. on October 2, an unfinished local zoning code is automatically rewritten, an ADU application is automatically approved, or a new statewide permit process takes over.

Another section matters here. Land Use §4-503 says that, except for the provisions of the new ADU subtitle, the subtitle does not alter or abrogate local zoning power or related authority; it also requires local jurisdictions to establish policies that further the intent of the subtitle.

The safest reading for homeowners

October 1 creates a mandatory local-law deadline. The statute itself does not provide a special October 2 homeowner remedy for a jurisdiction that misses it. That means you should not assume either extreme: that every old restriction automatically survives unchanged, or that every inconsistent restriction automatically vanishes.

How a particular post-deadline conflict would be resolved may depend on the local ordinance, the administrative decision being challenged, the jurisdiction’s appeal procedures and legal interpretation. That is precisely the point at which a research publication should stop short of predicting a legal outcome.

3. What HB 1466 does—and does not—guarantee after the deadline

What the statute clearly provides What the statute does not expressly provide
Local legislative bodies must adopt an ADU law by October 1, 2026. An automatic ADU approval if the jurisdiction misses the deadline.
The local ADU law must satisfy §4-504’s requirements and limitations. A statewide substitute permit issued in place of the local permit.
Additional ADU parking mandates require a prior parking study and a waiver process. A rule saying every existing local ADU provision disappears on October 2.
ADU side/rear setback requirements cannot exceed the jurisdiction’s existing accessory-structure setbacks. A single statewide numeric setback such as four feet.
ADUs remain subject to public health, safety, building-code and adequate-public-facilities provisions. An exemption from septic, well, fire, building or other applicable safety review.

Maryland Department of Planning also notes that HB 1466 does not specify how the 75% size limit must be measured. MDP recommends finished living area above grade, but local implementation can create important measurement questions. This is why a county’s final ordinance and code definitions still matter.

4. What if the local code appears to conflict with HB 1466?

Separate two questions before deciding what to do:

  1. What does Maryland law require the jurisdiction to enact? Start with Land Use §§4-501 through 4-504 and the Maryland Department of Planning implementation materials.
  2. What rule is the local department actually administering today? Check the enacted local ordinance, current zoning code, official legislative docket and written planning guidance.

Those two answers may not always match cleanly during the transition. Montgomery County is an unusually clear example: official 2026 Council material states that several provisions of its existing ADU law are inconsistent with state law, including allowable zones, minimum size, density, setbacks and off-street parking, while ZTA 26-06 remains the alignment measure.

A mismatch does not mean Maryland ADU Guide can tell a homeowner that a permit must be approved. Nor should a homeowner assume a verbal answer at the zoning counter is the final word on a legally disputed requirement. The useful next step is to create a written record.

5. Homeowner action plan if your jurisdiction is still in transition

  1. Check the current legislative status first. Determine whether the local measure is introduced, in committee, passed, signed, pending an effective date or already codified. Do not design from introduced text as though it were final.
  2. Ask for the currently administered rule in writing. Use the jurisdiction’s zoning-verification, administrative-interpretation or written-inquiry process, if available. Ask specifically which ADU provisions staff will apply to applications submitted after October 1.
  3. Cite the exact state provision you are asking about. For example, if the issue is additional parking, point to §4-504(e); if it is a side/rear setback, point to §4-504(d). This produces a much more useful written response than a general “Can I build an ADU?” question.
  4. Preserve the response and the date. Save emails, written determinations, application comments and any cited code section. Maryland’s rules are moving quickly, and the date of a staff interpretation matters.
  5. Do not ignore separate feasibility layers. A zoning issue is not the same as building-code, septic, well, stormwater or utility approval. Use our Maryland ADU Property Feasibility Checker and Septic & Well Guide before treating a favorable zoning answer as project approval.
  6. Act quickly on a written denial. If a permit or zoning request is formally denied based on a local provision that appears inconsistent with HB 1466, review the decision and any appeal deadline promptly. A Maryland land-use attorney can advise on administrative or legal remedies; an architect, engineer or land-use planner may separately help with technical site compliance.
Do not wait for a legal dispute to start documenting the project. A dated written response from the jurisdiction is substantially more useful than an undocumented phone conversation if the applicable rule later changes or is challenged.

6. Where the major tracked jurisdictions stand as of September 7, 2026

Jurisdiction Verified position What homeowners should know
Howard County 🟢 Enacted
CB3-2026 effective April 8, 2026		 Howard has completed its major 2026 ADU update. The county uses 75% of the exterior footprint of the principal dwelling for its local size calculation. Our Howard guide also flags a parking-source discrepancy between the public-facing county summary and the enacted legislative record.
Montgomery County 🟠 Transition
ZTA 26-06		 The County Council’s official ZTA list still shows ZTA 26-06 at Introduction. The PHP Committee reviewed it July 27. Official Council material says several existing ADU provisions are inconsistent with state law.
Prince George’s County 🟠 Transition
CB-074-2026 + CB-092-2026		 CB-074 was presented and referred July 7 and appeared before PHED September 3. CB-092 was presented and referred September 1 for additional non-zoning ADU requirements. We do not treat either proposal as final enacted law yet.
Anne Arundel County 🟠 Transition
Bill 61-26 pending		 Bill 61-26 was introduced July 20 and the official County Council page lists a hearing for September 8, 2026. The existing ADU framework remains important until final Council action and effective language are verified.
Baltimore County 🟡 Existing framework / alignment not yet verified Baltimore County still publishes its older accessory-apartment framework. In the official 2026 Council legislation and pending-legislation pages reviewed on September 7, we did not locate a final HB 1466 conforming ordinance. That is a research finding—not a declaration that the county is legally noncompliant.

These statuses can change quickly. The Maryland County ADU Rules Tracker is the site’s current-status layer; this article explains what the October 1 deadline itself does and does not mean.

7. A practical example: parking after October 1

Parking is a useful example because HB 1466 gives unusually specific instructions. A local legislative body may establish additional off-street parking requirements for ADUs, but before adopting that requirement it must complete a parking study. The law also requires the parking rule to consider specified cost, curb-space, impervious-surface and lot-size factors and to provide a waiver process.

If you encounter an additional ADU parking requirement after October 1, the useful research question is therefore not simply “Is this parking rule illegal?” It is:

Ask the jurisdiction: “What parking study supports this additional ADU off-street parking requirement, when was it completed, and where is the required waiver process published?”

That turns a vague disagreement into a source-checkable question grounded in the statute. We plan to apply the same method across county parking rules as local ordinances are finalized.

8. The bottom line

October 1, 2026 is a real statutory deadline, but it is not a magic date that answers every homeowner permitting question. Maryland law tells local legislative bodies what they must adopt and places important limits on local ADU regulation. It does not expressly create automatic approval, automatically rewrite every zoning book on October 2, or replace local permitting with a statewide permit.

If your jurisdiction is still transitioning, the safest process is to identify the enacted rule, compare it with the exact state provision, obtain the local interpretation in writing, preserve the record and seek qualified legal advice if a formal denial creates a genuine state/local-law conflict.

Start with the Maryland County ADU Rules Tracker, then open your county’s detailed guide before paying for final plans or committing to construction.

Primary sources used for this guide

Maryland ADU Guide is maintained by Gijo John as an independent research publication. We prioritize enacted statutes, local legislation, zoning materials and government guidance. Source-backed corrections can be sent to gijo.j@marylandaduguide.com.