1. What is the purpose of Accessory Dwelling Units – Requirements and Prohibitions (HB 1466)?
Maryland’s General Assembly passed HB 1466 during its 2025 legislative session. HB 1466 makes it the policy of Maryland to promote and encourage the creation of Accessory Dwelling Units (ADUs) on land with a single-family detached dwelling unit as the primary dwelling unit to help solve the state’s housing shortage and meet its housing needs. To accommodate all who want to live in the state, Maryland will need a mix of quality housing types and affordability options, and ADUs are an important part of that mix.
2. How does HB 1466 define an ADU?
HB 1466 defines ADUs as a secondary unit (1) on the same lot, parcel, or tract as a primary single-family detached dwelling unit and (2) that is not greater than 75% of the size of the primary single-family detached dwelling unit. The bill further states that ADUs can be a separate structure from the primary unit or attached as an addition to the primary unit. While not explicitly defined in the bill, jurisdictions may also permit ADUs that are wholly enclosed within the existing single-family dwelling.
3. When does HB 1466 go into effect?
The act became effective on October 1, 2025. The act includes a separate requirement that, by October 1, 2026, local governments adopt a local law authorizing development of ADUs on land with an existing single-family detached dwelling unit.
4. What does HB 1466 do?
The act defines ADUs, creates a statewide policy governing ADUs, requires that local governments adopt local laws authorizing development of ADUs, and prohibits documents such as deeds, bylaws of homeowner associations, and contracts from imposing unreasonable limitations on a property owner’s ability to develop an ADU or offer an ADU for rent.
5. How does HB 1466 modify local zoning?
HB 1466 modifies local zoning through its requirements for local laws authorizing the development of ADUs. See below for more information on those requirements.
6. What are the requirements for local laws governing ADUs?
Local laws must follow the intent of HB 1466, which is to promote and encourage ADUs. Such a law must:
Provide for the development of ADUs as defined in the bill and described in question two above
Provide for construction of ADUs that meet public health, safety, and welfare standards (such as building codes and adequate public facilities ordinances)
Exclude ADUs from density calculations
Exclude the development of an ADU from any measures that limit residential growth on the property on which the unit is proposed
The act states that a local law governing ADUs may not:
Impose additional parking requirements on ADUs without first completing a parking study to determine the jurisdiction’s parking needs
Establish side and rear setback requirements that exceed existing accessory structure setback requirements
The act states that a local law governing ADUs may:
7. Does HB 1466 require local laws to permit ADUs by right?
No, but a local government may establish a process that allows ADUs by right, or a local government may establish a process that requires a conditional use or special exception to confirm local requirements have been met. But it does require that local laws authorize ADUs in some manner. The Maryland ADU Policy Task Force recommended permitting “one internal or attached ADU by right on any lot in which a single-family residential unit is similarly permitted by right” as a best practice to support ADU development and lower the costs for property owners.
8. Can local laws be more permissive of ADUs than the requirements of HB 1466?
Yes, existing and future local laws governing ADUs can be more permissive than the requirements of HB 1466. This could include by-right approval, reduced or eliminated impact fees, or Adequate Public Facilities Ordinance exemptions. The ADU Policy Task Force Report includes many best practices to support ADU development that are more permissive than the requirements of HB 1466.
9. Does HB 1466 impose any requirements regarding lot size or residential density?
No, HB 1466 does not limit the size of the lot on which an ADU can be located, but it does limit the size of the ADU to no more than 75% of the size of the primary single-family dwelling unit. The act also requires that local laws governing ADUs exclude them from density calculations.
10. What is a parking study?
HB 1466 does not define the elements of a parking study, but it does require that any additional off-street parking requirements established for ADUs consider the following factors:
The cost of constructing off-street parking spaces
Whether sufficient curb area exists along the front line of properties to accommodate on-street parking
The increase in impervious surfaces due to the creation of new off-street parking and its relation to stormwater management
Variability in parking due to the size of the ADU’s lot.
HB 1466 requires that any local law requiring additional parking for ADUs shall provide a waiver process from the parking requirements.
The Maryland ADU Policy Task Force report (2024) includes several best-practice recommendations for parking policies related to ADUs so that parking requirements do not become an unreasonable barrier to ADU development.
11. Is my jurisdiction required to do a parking study to comply with HB 1466
The act requires that local jurisdictions complete a parking study only if their local laws governing ADUs impose additional off-street parking requirements on ADUs. If a jurisdiction’s local law does not impose additional off-street parking requirements on ADUs, it does not need to complete a parking study.
12. How does HB 1466 apply to historic districts and historic properties?
The act’s prohibition against restrictive covenants (such as deeds or bylaws) specifically exempts Maryland properties listed in or determined to be eligible for listing in the National Register of Historic Places. Historic neighborhoods often include housing types like what we now call ADUs, accommodating multi-family and multi-generational living configurations. In many cases, ADUs can be compatible with historic neighborhoods. The Maryland Historical Trust recommends that local governments utilize the Secretary of the Interior's Standards for Rehabilitation (particularly Standards 9 and 10) and consider historic precedents and local architectural styles and approaches when increasing density in historic neighborhoods. If you have additional questions regarding historic properties, please contact Nell Ziehl, Chief of the Office of Planning, Education, and Outreach at the Maryland Historical Trust, at [email protected].
13. My jurisdiction already has an ADU law. Does HB 1466 require that the law be changed?
If a jurisdiction’s existing ADU law complies with all of HB 1466’s requirements, it does not need to be changed. Local governments should confirm with their legal counsel whether their ADU laws comply with HB 1466. Any new legislation that a local jurisdiction must adopt to comply with HB 1466 must be adopted by October 1, 2026.
14. How does HB 1466 define “unreasonable limitations”?
HB 1466 addresses unreasonable limitations in its amendment of the Real Property Article rather than in its amendment of the Land Use Article. It defines them as any restriction on use that prohibits, either explicitly or by effect, a property owner from developing or offering an ADU for rent. The act’s definition of unreasonable limitations applies to covenants, deeds, or similar private legal documents.
15. Does HB 1466 prohibit HOAs from regulating ADUs?
HB 1466 prohibits HOA bylaws from imposing unreasonable limitations (defined above) on the ability of a property owner to develop an ADU or offer an ADU for rent. HOAs should consult with their legal counsel to determine whether their bylaws may impose an unreasonable limitation on ADUs.
16. Does HB 1466 require that HOAs allow the use of ADUs as short-term rentals?
HB 1466 specifies that, for the purposes of its amendment of the Real Property Article, an unreasonable limitation does not include a limitation on the short-term rental of an accessory dwelling unit.
17. Does HB 1466 allow local governments to regulate the use of ADUs as short-term rentals?
HB 1466 does not alter a local government’s powers to regulate short-term rentals.
18. How does HB 1466 affect existing ADUs?
HB 1466 is silent on the topic of existing ADUs. Once a county or municipality adopts a new ADU law meeting the requirements of HB 1466, some existing ADUs within its jurisdiction may not conform with the new requirements. To avoid confusion and burden for existing ADU owners, in consultation with the jurisdiction’s legal counsel, MDP recommends that local legislation recognize the legally existing ADUs and avoid deeming them as non-conforming. The ADU Policy Task Force addressed best practices for nonconforming ADUs on page 23 of its report.
19. Does Maryland state law require fire sprinklers to be added to ADUs?
State law requires residential fire sprinkler systems in all new single- and two-family residential dwellings, which would include newly constructed ADUs (Section 313.2 of the International Residential Code as referenced by COMAR 09.12.51.04A). While Maryland’s Attorney General has provided an opinion stating that no provision of state law currently requires fire sprinklers in manufactured homes (see Maryland’s Attorney General Opinion No. 107 OAG 74), local county or municipal building codes, or local laws governing ADUs, may have separate requirements regarding fire sprinklers. The State of Maryland Department of State Police, Office of the Fire Marshall, is responsible for licensing and regulating residential sprinkler systems. Contact the local government agency that administers the local building code, or the Office of the Fire Marshall, to determine how fire sprinkler requirements apply to a proposed ADU.
20. Where can I find more information about best practices for ADUs?
MDP maintains a webpage with a list of resources related to ADU policy, including the 2024 report published by Maryland’s ADU Policy Task Force. MDP will continue to update this page with additional guidance in coming months. If you have any other questions regarding ADUs that you think should be added to this document, please contact Carter Reitman, MDP’s Lead Housing Planner, at [email protected].
