Every Maryland County Has Until 1 October to Legalise ADUs

There is a date in Maryland law that most homeowners have not heard of and most county websites have not caught up with. On or before 1 October 2026, every legislative body in the state has to adopt a local law authorising accessory dwelling units on land zoned for single-family residential use. That is five weeks away at the time of writing. It comes from HB 1466, signed by Governor Moore on 22 April 2025 and effective that October, and it reaches charter counties as well as the rest. What it does not do is make ADUs legal by itself — the obligation lands on your county council, and what they adopt is what you will build under.

What the statute actually says

The operative sentence is short. Land Use Article § 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." Two things follow from that wording. First, it is a duty to adopt a law, not a self-executing right — if your county has not acted, you cannot walk into the permit office on 2 October waving the statute. Second, the law they adopt has to apply to all land in the jurisdiction zoned single-family residential, not a pilot area or a handful of opted-in districts. That is a meaningfully higher bar than the ward-by-ward approach some other cities have taken.

The four grounds a county can still say no on

The mandate is not unconditional. Under § 4–504(b) a local law applies provided the person developing the ADU owns the lot and has the exclusive right to use it, and provided new dwellings on that lot are not already prohibited because of limits on safe drinking water, limits on sewage disposal, or risks from fires, floods or landslides. Those are real constraints, not loopholes — on a septic lot in a rural county they may well be the reason you get a no, and that no is lawful. Separately, a council may set safety standards, and may prohibit converting an accessory structure whose only vehicle access is from an alley. That is close to the whole list of permitted carve-outs, which is why the statute is stronger than it first reads.

Your HOA covenant probably does not survive this

This is the part that catches people. The Act also amended the Real Property Article so that a restriction in an instrument affecting the transfer or sale of property cannot impose limits on developing or using an ADU on land zoned single-family residential. In plain terms: a covenant that bans accessory dwellings on your deed is, on its face, no longer doing what it was written to do. The trade is that a homeowners association is expressly allowed to treat an ADU as a separate lot for the purposes of voting and levying assessments — so expect the possibility of a second assessment rather than a veto. If your objection to building has been "the HOA will not allow it", that assumption is worth re-testing.

What this looks like on the ground: Harford County

Harford is a useful illustration of the distance some counties have to travel, and it is not a criticism of them — the deadline is the deadline for everyone. As the county code reads today, one ADU is allowed in the AG, RR, R1 through R4, RO and VR districts, but it must be physically attached to or inside the single-family house, so a detached cottage is not permitted. It is also relative-only: the owner must live in one unit as their permanent residence and the other must be occupied by the relative. It is capped at the lesser of 1,500 sq ft or 50% of the house's habitable space, limited to two bedrooms, and the zoning certificate becomes void if the property is sold or transferred. Whether a rule of that shape satisfies a statute requiring counties to authorise ADUs on all single-family land is a question for the County Council and its lawyers, and anyone telling you confidently either way right now is guessing. What is not in question is the date by which they have to answer it.

What to do between now and October

If you are thinking about an ADU in Maryland, the useful work in the next five weeks is not design. It is finding out three things. One: is your lot actually zoned single-family residential, because the mandate is scoped to that and nothing else. Two: is your lot served by public water and sewer, because the drinking-water and sewage grounds in § 4–504(b) are the most common lawful reason for a no. Three: has your county council introduced a bill yet — council filings are public, and a county that has introduced nothing by mid-September is a county whose rules you will be reading in October rather than August. Get those three answers and you will know whether you are waiting on paperwork or waiting on politics.