Maryland SB 891: The Statewide ADU Law and the October 1, 2026 Deadline

Maryland's S.B. 891 and its cross-file H.B. 1466 created the state's first statewide accessory dwelling unit mandate. Every county and municipality has to adopt a local ADU law by October 1, 2026. That deadline is now about ten weeks out. Two things about this law are consistently reported wrong: what it requires, and what happens if a jurisdiction ignores it. Here is the enacted text on both.

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Maryland enacted its ADU mandate as a pair of identical cross-filed bills in the 2025 session: S.B. 891 (Chapter 196), sponsored by Senators M. Washington and Kagan, and H.B. 1466 (Chapter 197), sponsored by Delegate Stewart and others. The Governor approved both on April 22, 2025, and both took effect October 1, 2025 [3][4].

One correction before anything else. There is no "Accessory Dwelling Unit Act of 2025." Both bills carry the official title "Land Use and Real Property – Accessory Dwelling Units – Requirements and Prohibitions," and neither contains a short-title section [2][3][4]. The "Act" name circulating in law firm write-ups and contractor blogs is shorthand somebody invented. It matters only because searching for it turns up secondary summaries of the introduced bill, which is a materially different document from the one that became law.

SB 891 at a Glance

Fact	What the statute says	Source
Bills and chapters	S.B. 891 (Ch. 196) and cross-file H.B. 1466 (Ch. 197), 2025 Regular Session	[3][4]
Official title	"Land Use and Real Property – Accessory Dwelling Units – Requirements and Prohibitions" (no short title)	[3][4]
Effective date	October 1, 2025; approved by the Governor April 22, 2025	[2][3]
Local adoption deadline	On or before October 1, 2026, each legislative body shall adopt a local ADU law	[1]
Who is covered	Every county and municipality with zoning authority, including charter counties and Baltimore City	[1][5][6]
Where it applies	Only land with a single-family detached dwelling unit as the primary dwelling unit	[1]
Size cap	ADU not greater than 75% of the size of and subordinate in use to the primary dwelling	[1]
ADU types covered	A structure separate from or attached as an addition to the primary dwelling	[1]
Density	Local law must exclude the ADU from density calculations and residential growth limits	[1]
Setbacks	Local law may not exceed the jurisdiction's existing accessory structure side/rear setbacks	[1]
Parking	Local law may add off-street parking requirements, but only after a parking study, and must include a waiver process	[1]
HOAs and covenants	Private restrictions may not unreasonably limit developing or renting an ADU (Real Property § 2–126)	[7]
Penalty for missing the deadline	None stated in the statute	[1][8]

Bottom Line

The operative law is short. S.B. 891 added a new Subtitle 5 to Title 4 of the Land Use Article, and that subtitle runs from § 4–501 to § 4–504. That is the whole thing [1].

Section 4–504(a)(1) is the mandate: "On or before October 1, 2026, each legislative body shall adopt a local law authorizing the development of accessory dwelling units in accordance with this section" [1]. The Department of Legislative Services reads "each legislative body" as every county and municipality, and the two conforming amendments in the bill pull the subtitle into charter counties (Land Use § 1–401(b)(19)) and Baltimore City (§ 10–103(b)(18)), which are otherwise carved out of this division of the Land Use Article [1][5][6][8]. So the reach is genuinely statewide. If your jurisdiction does zoning, it is on the hook.

What the mandate actually forces is narrower than the coverage suggests. A local law adopted under § 4–504 must do three things: provide for ADUs that meet public health, safety, and welfare standards including building codes and adequate public facilities provisions; exclude the ADU from density calculations and from any measures limiting residential growth; and refrain from setting side and rear setbacks stricter than the jurisdiction's existing accessory structure setbacks [1]. That is the complete list of requirements. Everything else, including height, lot coverage, design, permitting process, fees, owner-occupancy, and rental terms, stays local.

Myth	Reality
"The Accessory Dwelling Unit Act of 2025 legalized ADUs in Maryland."	There is no act by that name, and the law did not legalize anything directly. It requires each local government to pass its own ADU law by October 1, 2026. [1][3]
"The law bars unreasonable local restrictions."	The "unreasonable limitation" standard applies to private restrictions such as HOA rules and deed covenants, under Real Property § 2–126. It is not a limit on local zoning. [7]
"ADU permits get ministerial approval within 90 days."	That provision (§ 4–505 of the introduced bill) was amended out. It is not in the Code. [1][8]
"ADUs under 750 sq ft are exempt from impact fees."	Also amended out (§ 4–506 of the introduced bill). Not law. [1][8]
"The law applies to all land zoned single-family."	The enacted subtitle applies only to land that already has a single-family detached dwelling as the primary unit, not to a zoning category. [1]
"If my county misses the deadline, ADUs become legal by default."	Nothing in the statute says that. Maryland has no default rule. [1][8]

What the Law Requires Localities to Allow

Start with the definition, because it does more work than the mandate does. Under § 4–501(b), an accessory dwelling unit is a secondary dwelling unit that is on the same lot, parcel, or tract as a primary single-family detached dwelling unit, and "not greater than 75% of the size of and subordinate in use to" that primary dwelling. The definition then says an ADU "includes a structure that is separate from" or "attached as an addition to" the primary dwelling [1].

Two things follow. First, the 75% figure is a ceiling written into the definition itself, not a floor a locality has to grant. A jurisdiction can cap ADUs well below 75% and still comply. Second, the statute never says how "size" is measured. Square footage, gross floor area, and building footprint give very different answers on a two-story house, and the state left that choice to local drafters. Howard County measures against the exterior footprint of the principal dwelling [9]. Ask your jurisdiction which metric it adopted before you sketch anything.

Section 4–502 narrows the reach further: the subtitle "applies only to the development of accessory dwelling units on land with a single-family detached dwelling unit as the primary dwelling unit" [1]. The bill as introduced keyed off land zoned for single-family residential use. The enacted version keys off what is actually built on the lot. If your primary home is a townhouse, a semi-detached, or a duplex, the state mandate does not reach your property. Your locality may extend ADU rights to those housing types, and some do, but that is a local decision.

On the restriction side, § 4–504(d) is the one real preemption: a local law "may not establish setback requirements that exceed the existing accessory structure setback requirements from the side and rear lot lines" [1]. In plain terms, your county cannot demand more side and rear clearance for a backyard cottage than it already demands for a shed or a detached garage. Front setbacks and height are untouched.

Parking gets a procedural brake rather than a cap. Under § 4–504(e), a locality may impose additional off-street parking requirements, but only if it first completes a parking study of the jurisdiction's needs, and only if the local law includes a waiver process. The four factors the study must consider are listed in the statute: construction cost of the spaces, available curb area for on-street parking, added impervious surface and its relation to stormwater plans, and variability by lot size [1]. Note what is missing. There is no numeric ceiling. A jurisdiction that runs the study and writes a waiver process can require more than one space.

Localities also keep two express options under § 4–504(a)(2): they may set ADU safety standards, and they may prohibit converting an accessory structure into an ADU when the only vehicular access to it is from an alley [1].

What Got Cut Before Passage

This is where most published summaries of the Maryland law go wrong, and it is worth being precise about it.

The bill as introduced ran through § 4–507 and contained a much stronger set of homeowner protections. Three entire sections were struck by amendment before passage. The chaptered PDF on the General Assembly's site still prints them with strikethrough, which does not survive copy-paste, so they get quoted as if they were law [2].

Here is what is not in the Maryland Code. Section 4–505 would have required local jurisdictions to approve or deny a complete ADU zoning use permit application within 90 days and to perform approval "in a ministerial manner." Section 4–506 would have barred impact fees and building excise taxes on ADUs under 750 square feet, and required proportionality above that. Section 4–507 would have stopped utilities from requiring a separate water or sewer connection where the existing one is adequate, and from charging a connection fee for integrating the ADU. Several narrower prohibitions went with them, including a ban on requiring larger-than-minimum lot sizes, a parking cap tied to a 0.75-mile transit radius, and a ban on approval criteria based on subjective standards like neighborhood compatibility or adverse impacts [2].

You can verify this directly. The General Assembly's statute browser returns text for Land Use §§ 4–501, 4–502, 4–503, and 4–504, and returns "File Not Found" for §§ 4–505, 4–506, and 4–507 [1]. The Department of Legislative Services fiscal note, in its Third Reader revised version dated April 2, 2025, summarizes only the surviving provisions [8].

The practical effect is large. Maryland's law does not guarantee you a fast permit, does not shield you from impact fees, does not cap parking at a number, and does not stop a jurisdiction from evaluating your ADU against discretionary criteria. If someone quotes the 90-day ministerial rule to you, they are reading the wrong version of the bill.

The October 1, 2026 Deadline, and What Happens After It

The date is fixed in the operative text of § 4–504(a)(1) as currently codified, which is the cleanest evidence that no later session moved it [1].

Now the part that no official source will answer for you: nothing in Subtitle 5 says what happens to a jurisdiction that blows through October 1, 2026. There is no penalty. There is no state enforcement mechanism. There is no provision making ADUs legal by default, no provision suspending local zoning, and no cause of action against a non-complying county. The Maryland Department of Planning's own FAQ for local governments, which runs to more than twenty questions, does not address the consequence of non-compliance either [10].

The closest thing to a lever is § 4–503(b)(2): "Local jurisdictions shall establish policies that further the intent of this subtitle" [1]. That is a duty with no stated remedy attached.

Compare Nevada, which wrote the opposite. Under A.B. 396, a covered Nevada city that failed to adopt an ADU ordinance by its deadline must allow accessory dwelling units "on any parcel zoned for residential use without restriction" until it does. That is a self-executing consequence, and it changes the incentives entirely. Our guide to Nevada's AB 396 casita law walks through how that default rule works in practice. Maryland has no equivalent.

So the honest answer for a Maryland homeowner is that October 1, 2026 is a deadline for your county, not a date on which you gain a right. If your jurisdiction adopts a compliant local law, your rights come from that local law. If it does not, you are in territory the statute did not address, and the realistic paths are political pressure or litigation that nobody has yet tested. Do not plan a project around the assumption that the deadline itself unlocks anything.

HOAs, Deeds, and Covenants

This is the part of the Maryland law that has no counterpart in Nevada or Utah, and it is the reason the bill also amended the Real Property Article.

Real Property § 2–126 provides that if a property owner has the exclusive right to use the property and abides by all applicable laws and regulations, "a restriction on use regarding land use may not impose or act to impose an unreasonable limitation on the ability of the property owner to develop or offer for rent an accessory dwelling unit" [7]. "Restriction on use" is defined broadly, and expressly includes covenants, restrictions, or conditions in a deed, a declaration, a contract, the bylaws or rules of a homeowners association, a security instrument, or any other instrument affecting the transfer or sale of real property [7].

The statute then defines the standard in one direction only. An unreasonable limitation "includes a limitation that prohibits, either explicitly or by effect of the restrictions, the development of an accessory dwelling unit" [7]. The phrase "or by effect" is the operative one. A covenant does not have to say "no ADUs" to fall foul of the section; a stack of architectural rules that makes an ADU impossible can qualify.

Three limits deserve attention, because secondary coverage tends to skip all three.

The "significantly increases the cost" test is not law. The introduced bill defined an unreasonable limitation to include one that "significantly increases the cost of developing an accessory dwelling unit." That prong was struck by the same round of amendments that removed §§ 4–505 through 4–507, and the enacted text keeps only the prohibition prong [2][7][8]. An HOA rule that makes your ADU expensive but not impossible is on much weaker ground than the write-ups suggest.

Short-term rental restrictions survive untouched. Section 2–126(b)(2)(ii) says an unreasonable limitation "does not include a limitation on the short-term rental of an accessory dwelling unit" [7]. Your HOA can let you build the unit and still forbid you from listing it nightly.

Historic property is carved out entirely. The section does not apply to a restriction on use on historic property listed in, or determined by the Director of the Maryland Historical Trust to be eligible for inclusion in, the Maryland Register of Historic Properties [7].

And the law gave associations something back. Real Property § 11B–111.11 lets an HOA's governing body treat an ADU as a separate lot for purposes of voting on association matters, notwithstanding anything in the declaration, bylaws, deeds, or recorded covenants. Section 11B–117(a)(2)(ii) lets it treat the ADU as a separate lot for levying assessments, notwithstanding provisions capping or restricting assessment increases [7]. If you build an ADU in a Maryland HOA, expect a second assessment. That is now expressly authorized.

Who Is Complying, Who Is Lagging, and How to Check Yours

Maryland did not start from zero. During the Accessory Dwelling Unit Policy Task Force's work, created by Chapters 798 and 799 of 2023 and staffed by the Department of Planning, MDP inventoried 155 counties and municipalities and found that 81 of them, about 52%, already had some form of ADU provision in their zoning regulations [8]. MDP's FAQ confirms that a jurisdiction whose existing ADU law already meets every HB 1466 requirement does not need to change it [10]. So a jurisdiction can be silent this year and still be compliant, which makes headcounts of "who has passed a bill" a poor proxy for who is ready.

Two jurisdictions are worth naming because their status is documented on official pages.

Howard County has adopted. Council Bill 3-2026 was signed February 6, 2026 and took effect April 8, 2026, and the county's own page states it aligns the zoning regulations with the state's ADU law. It allows attached and detached ADUs, plus conversion of existing space to an attached ADU, in various residential districts [9]. It is also a useful reminder that compliant does not mean permissive. Howard caps the unit at 75% of the principal dwelling's exterior footprint, requires the owner to live in either the principal dwelling or the ADU, limits lots to one ADU, bars short-term rental of the unit, and, by amendment, raised the off-street parking requirement from one space to three, with exceptions [9].

Baltimore City has not. The city's ADU changes are folded into Council Bill 25-0066, the Housing Options and Opportunity Act, introduced May 12, 2025. As of the city's own legislative record, the bill remains in committee, and the most recent logged action is a Land Use and Transportation Committee worksession on February 12, 2026 [11].

Elsewhere the picture is mixed, and we are not going to publish a county-by-county table built on news coverage. Several counties that already had ADU ordinances are amending them, and at least a couple that had nothing are drafting from scratch under real time pressure. Some of that work is at the staff-report or planning-board stage rather than adopted.

Checking your own jurisdiction is straightforward, and more reliable than any list:

1. Start with MDP's ADU page. The Department of Planning publishes a Model Local ADU Ordinance and assessment tool, an Inventory of ADU Ordinances in Maryland, and the HB 1466 FAQ for local governments [10]. The inventory is the pre-mandate baseline, so treat it as a starting point rather than current status.
2. Search your county or city council's legislative portal for "accessory dwelling unit" restricted to 2025 and 2026. Most Maryland jurisdictions run Legistar or an equivalent, and the action log tells you whether a bill was adopted, is in committee, or died.
3. Call the planning department and ask three specific questions. Has the jurisdiction adopted its § 4–504 local law, and on what date is it effective? How does the ordinance measure the 75% size cap? Did the jurisdiction complete a parking study, and what is the waiver process?
4. Read the adopted ordinance, not the press release. Owner-occupancy, short-term rental bans, one-ADU-per-lot limits, lot coverage, and height all live in local text and none of them are preempted by the state law.

What To Do Now

1. Confirm the lot qualifies. The state mandate reaches land with a single-family detached dwelling as the primary unit. Attached, semi-detached, and two-family primaries are outside it unless your locality went further [1].
2. Find out whether your jurisdiction has adopted its local law, and get the effective date in writing. Before that ordinance exists, the state statute gives you no self-executing right to build [1].
3. Pin down the size metric. Seventy-five percent of "size" means nothing until your ordinance defines the measurement. Get it in writing before designing [1][9].
4. Ask about parking early. A jurisdiction that completed a study can require more than one space, as Howard County's three-space amendment shows. Ask what the waiver process requires [1][9].
5. Read your HOA declaration and your deed. Real Property § 2–126 helps you against a covenant that prohibits an ADU outright or by effect, but it does not help against a short-term rental ban, does not apply on listed or eligible historic property, and does not stop the association from assessing the ADU as a separate lot [7].
6. Budget for fees. The impact fee exemption people cite was cut from the bill. Assume standard local permitting and impact fees apply unless your ordinance says otherwise [2][8].
7. Pressure-test the numbers on your actual lot. If you want to see whether a Maryland ADU pencils given your setbacks, size cap, and parking requirement, start with whether you can build an ADU on your specific property.

Frequently Asked Questions

Is Maryland's ADU law in effect now? Yes, but not in the way most people mean. Chapters 196 and 197 took effect October 1, 2025. What they created is a duty for local governments to adopt their own ADU laws by October 1, 2026. Your ability to build comes from your county or city ordinance, not directly from the state statute [1][3][4].

Which Maryland jurisdictions have to comply? Every county and municipality with zoning authority. The bill added conforming amendments extending the subtitle to charter counties and to Baltimore City, which are otherwise excluded from this division of the Land Use Article, so the mandate is statewide [1][5][6][8].

What happens on October 2, 2026 if my county did nothing? The statute does not say, and neither does the Department of Planning's FAQ. There is no penalty, no state enforcement provision, and no default rule legalizing ADUs. This is a real gap in the law, not an oversight in our reading of it [1][8][10].

Does the state law let my county require owner-occupancy? Yes. Owner-occupancy is not addressed in Subtitle 5 at all, which leaves it to local choice. Howard County requires the owner to live in either the principal dwelling or the ADU [1][9].

Can my HOA charge me a second assessment for the ADU? Yes. Real Property § 11B–117(a)(2)(ii) expressly authorizes a homeowners association to treat an accessory dwelling unit as a separate lot for purposes of levying assessments, overriding declaration provisions that cap or restrict assessments. Section 11B–111.11 does the same for voting [7].

Is there a 90-day permit guarantee? No. That provision was in the bill as introduced and was amended out before passage. Land Use §§ 4–505 through 4–507 do not exist in the Maryland Code [1][2][8].

Does the law cover an interior basement conversion? The enacted definition says an ADU "includes" a structure separate from or attached as an addition to the primary dwelling. That wording is inclusive rather than exhaustive, and the explicit interior-conversion language from the introduced bill was removed, so the state definition does not clearly guarantee interior conversions. Many local ordinances allow them anyway. Ask your jurisdiction rather than relying on the state text [1][2].

References

1. [1] Maryland General Assembly, "Statutes Text — Article: Land Use, Title 4, Subtitle 5 (Accessory Dwelling Units)." Primary source for the ADU definition and 75% size cap (§ 4–501), the single-family-detached-primary limitation (§ 4–502), the State policy and preservation of local zoning power (§ 4–503), and the October 1, 2026 adoption mandate with its density, setback, and parking provisions (§ 4–504). The same browser returns "File Not Found" for §§ 4–505, 4–506, and 4–507, confirming those sections are not codified. https://mgaleg.maryland.gov/mgawebsite/Laws/StatuteText?article=glu&section=4-504&enactments=false
2. [2] Maryland General Assembly, "Chapter 196 (Senate Bill 891) — Chaptered bill text, 2025 Laws of Maryland." Enrolled text showing struck and inserted language, including the deleted §§ 4–505 (90-day ministerial approval), 4–506 (impact fee and excise tax limits), and 4–507 (utility connection limits), the deleted "significantly increases the cost" prong of Real Property § 2–126, and Section 2's October 1, 2025 effective date. https://mgaleg.maryland.gov/2025RS/chapters_noln/Ch_196_sb0891T.pdf
3. [3] Maryland General Assembly, "Legislation — SB0891, 2025 Regular Session." Official title, Chapter 196 designation, sponsors (Senators M. Washington and Kagan), designated cross file HB1466, and October 1, 2025 effective date. https://mgaleg.maryland.gov/mgawebsite/Legislation/Details/SB0891?ys=2025RS
4. [4] Maryland General Assembly, "Legislation — HB1466, 2025 Regular Session." Confirms the identical official title, Chapter 197 designation, sponsorship by Delegate Stewart and others, the SB0891 cross file, and the April 22, 2025 approval date. https://mgaleg.maryland.gov/mgawebsite/Legislation/Details/HB1466?ys=2025RS
5. [5] Maryland General Assembly, "Statutes Text — Land Use § 1–401." Lists Title 4, Subtitle 5 (Accessory Dwelling Units) at subsection (b)(19) as a provision of Division II that applies to charter counties. https://mgaleg.maryland.gov/mgawebsite/Laws/StatuteText?article=glu&section=1-401&enactments=false
6. [6] Maryland General Assembly, "Statutes Text — Land Use § 10–103." Lists Title 4, Subtitle 5 (Accessory Dwelling Units) at subsection (b)(18) as a provision applying to Baltimore City. https://mgaleg.maryland.gov/mgawebsite/Laws/StatuteText?article=glu&section=10-103&enactments=false
7. [7] Maryland General Assembly, "Statutes Text — Article: Real Property § 2–126," with §§ 11B–111.11 and 11B–117. Source for the definition of "restriction on use," the unreasonable-limitation standard and its prohibition-only prong, the short-term rental carve-out, the Maryland Historical Trust exception, and the HOA authority to treat an ADU as a separate lot for voting and assessments. https://mgaleg.maryland.gov/mgawebsite/Laws/StatuteText?article=grp&section=2-126&enactments=false
8. [8] Maryland Department of Legislative Services, "Fiscal and Policy Note, Third Reader – Revised, Senate Bill 891 (2025 Session)," revised for amendments April 2, 2025. Confirms the enacted scope ("each legislative body of a local jurisdiction (county or municipality)"), summarizes only the surviving requirements, and reports the MDP inventory finding that 81 of 155 counties and municipalities (52%) already had ADU provisions. https://mgaleg.maryland.gov/2025RS/fnotes/bil_0001/sb0891.pdf
9. [9] Howard County Department of Planning and Zoning, "Accessory Dwelling Units (ADUs)." Council Bill 3-2026 signed February 6, 2026 and effective April 8, 2026; alignment with Maryland HB 1466; the 75%-of-exterior-footprint size cap, owner-occupancy requirement, one-ADU-per-lot limit, short-term rental prohibition, and the amendment raising off-street parking from one space to three. https://www.howardcountymd.gov/planning-zoning/accessory-dwelling-units-adus
10. [10] Maryland Department of Planning, "Accessory Dwelling Units" and "ADU FAQ for Local Governments (HB 1466)." State guidance restating the October 1, 2026 deadline and the required contents of a local law, confirming that an existing compliant ordinance need not be changed, and containing no discussion of penalties or default rules for non-compliance. Also the source for the Model Local ADU Ordinance and the Inventory of ADU Ordinances in Maryland. https://planning.maryland.gov/Pages/OurWork/PBP/ADUTF/ADU.aspx
11. [11] Baltimore City Council, "File #25-0066 — Zoning – Housing Options and Opportunity." Official legislative record showing introduction May 12, 2025, committee assignment, and a most-recent action of a Land Use and Transportation Committee worksession on February 12, 2026, with the bill still in committee. https://baltimore.legistar.com/LegislationDetail.aspx?GUID=BD3D4C61-F699-49A3-B84C-9EDA59D2C005&ID=7397288

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