Maryland's ADU Deadline Is October 1, 2026 — What Every County Must Do

Every county and municipality in Maryland with planning and zoning authority has until October 1, 2026 to adopt a local law authorizing accessory dwelling units. That is not a recommendation or a funding incentive — it is a statutory deadline, and it applies to charter counties too. If you own a single-family home in Maryland and have been told an ADU is not allowed on your lot, the answer may change this autumn. Here is what the law actually says, taken from the enrolled text rather than a summary.

The deadline, in the statute's own words

Maryland HB 1466 was signed by Governor Moore on April 22, 2025 and took effect on October 1, 2025 as Chapter 197. It added a new subtitle — Title 4, Subtitle 5, "Accessory Dwelling Units" — to the Land Use article of the Annotated Code. The operative sentence is § 4-504(a)(1): "On or before October 1, 2026, each legislative body shall adopt a local law authorizing the development of accessory dwelling units on land zoned for single-family residential use in accordance with this section." The word is shall, not may. And because the Act added Title 4, Subtitle 5 to the list at § 1-401(b), it reaches charter counties — which is most of Maryland's population, including Montgomery, Prince George's, Baltimore, Howard, Anne Arundel and Harford.

What a compliant local law has to cover

The statute does not simply tell councils to write something. § 4-504(b) says a local law adopted under it shall apply to all land in the jurisdiction zoned for single-family residential use, subject to two conditions: the party developing the ADU owns and has the exclusive right to use the lot, and development of new dwelling units on that lot is not otherwise prohibited because of limits on safe drinking water, limits on sewage disposal, or risks associated with fires, floods or landslides. Those are the carve-outs the legislature wrote down. A local law that instead permits ADUs on a narrow subset of single-family land is doing something the statute does not obviously authorize — though whether any particular ordinance satisfies § 4-504 is a question for that county's lawyers and ultimately its courts, not for a website.

What councils are still allowed to restrict

Two things are expressly preserved. Under § 4-504(a)(2) a legislative body may adopt a local law that establishes standards for ADU safety, and may prohibit the full or partial conversion of an accessory structure into an ADU if the only vehicular access to that structure is from an alley. That second one is unusually specific and worth knowing if your garage backs onto an alley, which describes a great deal of older housing stock in Baltimore and inside the Beltway. Beyond safety standards and the alley rule, the statute's list of permitted local restrictions is short.

Your HOA covenant probably just stopped working

This is the part most homeowners miss. The Act also amended the Real Property article. A restriction on use in an instrument affecting the transfer or sale of real property — a deed covenant, in plain terms — may no longer impose or act to impose limits on the development or use of an ADU on property zoned single-family residential. Separately, a homeowners association governing body is authorized to treat an ADU as a separate lot for the purposes of voting and levying assessments. So the covenant that bans a second dwelling is on much weaker ground than it was, but your HOA may be entitled to assess the ADU. Read both halves before you assume you have won or lost.

Why your county's current rules may not survive this

Plenty of Maryland jurisdictions already have something on the books called an accessory dwelling unit, and it is easy to assume that means the work is done. Harford County is a useful illustration of why that assumption is worth checking. Its zoning code permits one ADU in the AG, RR, R1 through R4, RO and VR districts — but the unit must be physically attached to or located within the single-family house, so a detached cottage is not permitted at all. Its stated purpose is to let a relative live in the unit, and the code requires that the owner occupy one of the two dwellings while the other is occupied by the relative. The zoning certificate becomes null and void if the property is transferred, conveyed or assigned. That is a real ADU provision, written in good faith, and it looks very different from a law authorizing ADU development on all land zoned single-family residential. Whether it satisfies § 4-504 is for the County Council to work through before October — but if you are a Harford homeowner planning a detached build, that gap is the thing to watch.

What to do between now and October

If you are planning an ADU in Maryland, three things are worth doing now rather than in the autumn. First, confirm your lot is zoned single-family residential and that you hold it outright — those are the statutory preconditions and nothing else matters if they fail. Second, check whether your site has a genuine water, sewage or flood constraint, because those are the grounds on which a county may still say no. Third, watch your county council's bill filings: a rewrite, if one is coming, will surface there and it is public. Contractors are worth talking to early for feasibility, but be wary of anyone quoting a firm price against rules that have not been adopted yet.