In plain words

Maryland has a statewide ADU law. An accessory dwelling unit (ADU) is a small second home on the same lot as a house. Under the state law it is an addition to the house or a separate building, like a backyard cottage. Your county or town may also allow a unit inside the house, such as a basement apartment, but the state does not require that. In 2025 the state passed HB 1466 (its twin is SB 891). The law took effect October 1, 2025. It told every county and city that controls zoning to pass its own ADU law by October 1, 2026. Zoning means the local rules about what you can build where. The state rules cover lots where the main home is a single-family detached house. An ADU can be no bigger than 75% of the main house. Local governments may not count an ADU against density limits, which are caps on homes per acre. They may not set side or rear setbacks (the required distance from property lines) stricter than for a garage or shed. They may require extra parking only after a parking study, and they must offer a waiver. The state did not require approval 'by right', meaning a staff sign-off with no hearing. So your county may still require a special hearing. The state law is silent on owner occupancy (a rule that the owner live on the property), so some counties keep it. Rules of a homeowners association (HOA) and deed restrictions cannot unreasonably block you from building or renting an ADU, but they can still ban short-term rentals. Each county and town writes its own ordinance, so details depend on where you live. You may be able to build one if your local rules and your property allow it.

The rules at a glance

State ADU lawYes
Where the state rule appliesEvery county (including charter counties such as Montgomery and Prince George's) and every municipality with planning and zoning authority, plus Baltimore City. The rules cover land where the primary home is a single-family detached house.
Approved without a hearing?No. Towns can still require hearings or special permits.
Kinds of ADU the state protectsattached, detached
ADUs per lotNot fixed by statute. Local laws must authorize ADUs on qualifying single-family detached lots; localities may allow more than one.
Owner living on siteTowns may require the owner to live on the property.
ParkingA local law may add off-street parking requirements for ADUs only after the jurisdiction completes a parking study. The rule must weigh the cost of building parking, available curb space in front of the lot, added paved surface and stormwater, and differences in lot size, and it must offer a waiver process.
SizeAn ADU can be no more than 75% of the size of the main single-family detached house and must be subordinate in use to it. The statute does not say how to measure size; the Maryland Department of Planning recommends using the main home's finished living area above grade. There is no state minimum size and no fixed square-foot cap.
Lot size and setbacksLocal side and rear setbacks for an ADU cannot be stricter than the setbacks already applied to other accessory structures, such as garages or sheds. ADUs must be left out of density calculations and out of any growth-limit measures for the lot. A locality may bar converting an accessory structure into an ADU when the only vehicle access to it is from an alley.
FeesState law doesn’t set this. Earlier drafts of HB 1466 waived impact fees for ADUs under 750 sq ft and limited water and sewer hookup charges, but those sections were removed before passage.
Short-term rentalsLocal governments keep their power to regulate short-term rentals. HOA rules and deed restrictions may still limit short-term rental of an ADU even though they cannot unreasonably limit long-term renting.
Can towns opt out?No

What to do next

  1. Call your county or city planning and zoning office and ask for its ADU ordinance adopted under HB 1466 (the deadline was October 1, 2026).
  2. Confirm your lot qualifies: the main home must be a single-family detached house, and well, septic, floodplain or historic rules can add limits.
  3. Plan the ADU at no more than 75% of your home's size, then check local height, setback and lot-coverage limits.
  4. Ask whether your jurisdiction approves ADUs by staff permit or requires a public hearing (often called a conditional use or special exception), and budget time for any hearing.
  5. Read your HOA documents and deed; they cannot unreasonably block an ADU but may limit short-term rentals.
  6. Apply for building permits; new ADUs must meet the state building code, including fire sprinklers in new construction.

What your town still decides

Before 2025 Maryland left ADUs entirely to local governments; a Department of Planning inventory found 81 of 155 counties and towns (52%) had some ADU provision. HB 1466 keeps local zoning power except where the law says otherwise, and tells local governments to set policies that further its intent. A county or town can still send ADU applications through a conditional use or special exception hearing, set safety standards, and be more generous than the state floor. The Department of Planning published a model ordinance, a compliance assessment tool and an FAQ for local governments. The adoption deadline was October 1, 2026, two days before this check, so many local ordinances were newly adopted or still being finalized. Separately, HOA rules and private covenants cannot unreasonably restrict building or renting an ADU (historic properties on or eligible for the Maryland Register are exempt), and an HOA may count an ADU as a separate lot for voting and assessments. State law generally requires fire sprinklers in new one- and two-family homes, and the Department of Planning says that includes newly built ADUs. Some counties, such as Montgomery, also require the owner to live on the property; the state law is silent on that.

Examples of local rules

  • Montgomery County: ADUs have been legal in several single-family zones for years. Since 2019 they are approved by staff with a county rental license, and the owner has to live on the property, in the main home or the ADU. A detached ADU can be as large as the smallest of 10% of the lot, half the main home's footprint, or 1,200 sq ft, and no extra parking space is required within a mile of Metro, Purple Line or MARC stations. The county issued 222 ADU permits from 2019 to 2025. Zoning Text Amendment 26-06, introduced April 21, 2026, would change the allowed zones, size rule, setbacks and parking to match HB 1466; the Council was expected to vote on it in mid-September 2026, but the final vote was not confirmed in this check. A separate bill, Bill 41-26, would drop the owner-occupancy rule and waive county fees for ADUs rented at affordable rents; its public hearing was set for October 6, 2026. Source
  • Prince George's County: The County Council created an ADU Task Force (Resolution CR-091-2025, adopted October 7, 2025) to recommend how to carry out the state law. Its work led to Council Bill CB-074-2026, which the Council enacted on September 29, 2026 to set the county's ADU rules. An advocacy group's summary of the introduced draft said it allowed an ADU without a special hearing on single-family detached lots, up to 75% of the house's size and 22 feet tall. The bill was amended in committee on September 3, 2026, so read the enacted text before you plan. Source

What we’re still confirming

  • Which counties and towns adopted ADU rules by the October 1, 2026 deadline isn't known, and the law sets no penalty for missing it.
  • State law doesn't mention owner occupancy, so your county or town may still require the owner to live on site.

Laws, bills and citations

The laws behind this (2)
  • Land Use and Real Property - Accessory Dwelling Units - Requirements and Prohibitions (Md. Code, Land Use §§4-501 to 4-504, 1-401(b)(18), 10-103(b)(17); Real Property §§2-126, 11B-101(a-1), 11B-111.11, 11B-117(a) / HB 1466 (2025 Laws ch. 197) and identical cross-file SB 891 (2025 Laws ch. 196), signed April 22, 2025, in effect October 1, 2025). Makes it state policy to encourage ADUs on lots where the main home is a single-family detached house, and orders every county and city with zoning power (including charter counties and Baltimore City) to adopt a local ADU law by October 1, 2026. Caps an ADU at 75% of the main home's size, keeps ADUs out of density counts, limits side and rear setbacks and parking demands, and bars HOA rules and deed restrictions from unreasonably blocking an owner from building or renting an ADU. The law's definition covers an ADU built as an addition to the house or as a separate structure; it does not expressly cover a unit inside the existing house, which local governments may choose to allow. Read it
  • Accessory Dwelling Unit Policy Task Force (SB 382 (2023 Laws ch. 799) and cross-file HB 239 (2023); the fiscal note for HB 1466 cites Chapters 798 and 799 of 2023, signed May 28, 2023, in effect June 1, 2023). Created a temporary state task force, staffed by the Maryland Department of Planning, to study state and local ADU rules and recommend changes. Its final report (May 31, 2024) fed into the 2025 law. It did not change what homeowners could build. Read it
Proposed and failed bills (3). None of these is law.
  • HB 1538 (2026 Session): died as of October 3, 2026. The 'Maryland Generational Housing Act of 2026' would have required local laws to allow at least one internal and one external ADU on qualifying lots regardless of density limits, limited parking requirements, barred certain utility fees, and let ADUs share meters and service lines with the main home. It got a committee hearing date (March 13, 2026) but no vote before the session ended. Bill page
  • HB 1236 (2026 Session): died as of October 3, 2026. Would have let properties inside locally designated historic districts keep private restrictions on ADUs, carving them out of the 2025 rule that stops HOAs and deeds from blocking ADUs. Scheduled for a March 13, 2026 hearing; no further action. Bill page
  • HB 239 / SB 36 (2026 Session): died as of October 3, 2026. The Governor's 'Starter and Silver Homes Act of 2026' would have stopped local governments from enforcing certain lot-size, setback, lot-coverage and design rules on some single-family homes and from banning certain housing types. It was not ADU-specific. Neither version left committee. Bill page

Sources

  1. Md. Code, Land Use §§4-501 to 4-504, 1-401(b)(18), 10-103(b)(17); Real Property §§2-126, 11B-101(a-1), 11B-111.11, 11B-117(a) / HB 1466 (2025 Laws ch. 197) and identical cross-file SB 891 (2025 Laws ch. 196) · official source
  2. SB 382 (2023 Laws ch. 799) and cross-file HB 239 (2023); the fiscal note for HB 1466 cites Chapters 798 and 799 of 2023 · official source
  3. Md. Code, Land Use §4-501 (ADU definition: 75% size cap; attached or separate structure) · official source · checked 2026-10-03
  4. Md. Code, Land Use §4-504 (October 1, 2026 local law deadline; density, setback and parking-study rules) · official source · checked 2026-10-03
  5. Md. Code, Real Property §2-126 (deed and HOA restrictions on ADUs; short-term rental and Maryland Register historic exemptions) · official source · checked 2026-10-03
  6. MACo Conduit Street, 2026 End of Session Wrap-Up: Housing and Community Development (HB 1538 and HB 239/SB 36 failed) · checked 2026-10-03
  7. 2025 Laws of Maryland, Chapter 197 (HB 1466) text · official source · checked 2026-10-03
  8. HB 1466 Fiscal and Policy Note (Third Reader, Revised) · official source · checked 2026-10-03
  9. SB 891 (2025) bill page, Chapter 196 · official source · checked 2026-10-03
  10. Maryland Department of Planning, Accessory Dwelling Units · official source · checked 2026-10-03
  11. Maryland Department of Planning, HB 1466 FAQ for Local Governments · official source · checked 2026-10-03
  12. HB 1538 (2026) Maryland Generational Housing Act · official source · checked 2026-10-03
  13. HB 1236 (2026) historic district exemption · official source · checked 2026-10-03
  14. SB 36 (2026) Starter and Silver Homes Act · official source · checked 2026-10-03
  15. HB 239 (2026) Starter and Silver Homes Act · official source · checked 2026-10-03
  16. Baltimore Regional Housing Partnership, 2026 Legislative Wrap-Up (HB 239/SB 36 died) · checked 2026-10-03
  17. Montgomery Planning staff report, ZTA 26-06 Accessory Dwelling Units (May 2026) · official source · checked 2026-10-03
  18. Prince George's County Council Resolution CR-091-2025 (ADU Task Force) · official source · checked 2026-10-03
  19. Maryland DHCD notice, Housing Innovation Pilot Program (checked; not an ADU or homeowner program) · official source · checked 2026-10-03
  20. Montgomery County Council press release on ZTA 19-01 (2019 ADU rules, owner must live on site) · official source · checked 2026-10-03
  21. Montgomery County Council release for the September 15, 2026 meeting (ZTA 26-06 vote expected; Bill 41-26 owner-occupancy repeal and fee waiver) · official source · checked 2026-10-03
  22. Prince George's County Council, CB-074-2026 Accessory Dwelling Units (Legistar) · official source · checked 2026-10-03
  23. Prince George's CB-074-2026 legislative history, enacted September 29, 2026 (Legistar web API) · official source · checked 2026-10-03
  24. Coalition for Smarter Growth, Action alert: Support ADUs in Prince George's (August 31, 2026; summary of the CB-74 draft) · checked 2026-10-03

This is general information, not legal advice. Your town, village, city or county decides what can be built on your property. If something here looks out of date, email the team.