Maryland ADUs in Historic Districts: HB 1466, Design Review & HB 1236

Quick answer: Historic status does not create one simple statewide “yes” or “no” answer for a Maryland ADU. A property can be eligible for an ADU under HB 1466 and still need separate historic-preservation review. The first question is what kind of historic status applies: a local historic district, an individually designated local landmark, a property listed in or eligible for the Maryland/National Register, or a private deed/covenant restriction. Those categories can trigger different rules.

Last verified: September 19, 2026. Historic-property review is highly property-specific. This guide is for homeowner planning and is not legal, architectural or preservation advice.

Maryland historic-property ADU rules at a glance

Start by identifying which historic-status layer applies

“Historic property” is too broad a label for permit planning. A homeowner should first identify whether the property is subject to one or more of these layers:

• Local historic district: created and administered by a county or municipality under its local preservation law.
• Local landmark / individually designated property: a specific property protected under local law.
• Maryland Register / National Register property: state/federal historic recognition that can affect certain legal protections, reviews and incentives.
• Private covenant, deed restriction or HOA rule: a private restriction that is separate from government historic-design review.
• Tax-credit / grant participation: a rehabilitation project receiving preservation incentives can have additional standards and approval conditions.

These categories can overlap. A house may be inside a local historic district, contribute to a National Register district, and also be subject to an HOA declaration. Treat each layer separately.

What HB 1466 actually changed for historic property

Maryland HB 1466 created statewide policy supporting ADUs and limited the ability of certain private restrictions—such as deeds, declarations, contracts and HOA bylaws—to unreasonably prevent an owner from developing or renting an ADU.

But Maryland Real Property §2-126 contains a specific historic-property exception. The statute says its restriction-on-use protection does not apply to qualifying historic property listed in or determined eligible for the Maryland Register of Historic Properties.

Maryland Department of Planning’s HB 1466 FAQ explains the issue using National Register language and notes that historic neighborhoods often already contain small secondary buildings, carriage houses and other housing forms similar to modern ADUs. MDP also says ADUs can often be compatible with historic neighborhoods.

For the broader statewide ADU rules, see the Maryland ADU Laws 2026 guide. For HOA/private-restriction questions, use the Maryland ADU HOA guide.

HB 1466 does not erase local historic-design review

A separate issue is the local government’s historic-preservation authority. Cities and counties can require historic-design review for exterior changes, additions, demolition or new construction within locally regulated historic districts.

That means a homeowner can have a zoning path for an ADU and still need a second approval for the design. Depending on the jurisdiction, that approval may be called a Certificate of Appropriateness, Historic District Commission approval, CHAP approval, or another preservation-review decision.

Historic review can focus on issues that a normal ADU zoning table does not answer:

• where the detached ADU sits in relation to the historic house;
• whether it is visible from the public street;
• height, massing, roof shape and scale;
• window and door proportions;
• exterior materials and detailing;
• attachment points for an addition;
• demolition or alteration of a historic garage, carriage house or outbuilding;
• landscape/site changes that affect the historic setting.

This is why “ADUs are allowed in my zoning district” is not the same thing as “this ADU design will be approved on my historic property.”

Why Standards 9 and 10 matter for an ADU

Maryland Planning says the Maryland Historical Trust recommends using the Secretary of the Interior’s Standards for Rehabilitation—particularly Standards 9 and 10—when local governments evaluate additional housing in historic neighborhoods.

In homeowner language, those standards push a project toward two goals:

For a detached ADU, this can translate into keeping the new structure visually subordinate to the main historic house, locating it toward the rear where appropriate, and avoiding a design that overwhelms or falsely imitates the original building.

For an attached ADU, reviewers can be especially sensitive to where the addition connects, whether important historic material is removed, and whether the historic form remains legible.

What happened to Maryland HB 1236 in 2026?

House Bill 1236 was introduced in the 2026 General Assembly session to expand the historic-property exception in Maryland’s ADU private-restriction law. The bill proposed adding properties located within a district designated by a local jurisdiction as historically significant.

As of September 19, 2026, the General Assembly record still shows HB 1236 in the House after a March 13 Economic Matters hearing. It did not pass both chambers or become law in the published legislative history.

Which ADU type is easiest on a historic property?

There is no universal answer, but the type of ADU changes the preservation questions.

If an existing garage or carriage house is involved, do not assume conversion is automatically easier than new construction. The structure can have its own historic significance and the building-code conversion work may require visible alterations. Use the Maryland garage-conversion guide and the Maryland ADU building-code guide together.

Maryland places where historic review can matter

Historic-preservation review is already a real ADU planning issue across multiple Maryland jurisdictions. Our local guides document examples including:

• Annapolis — City zoning plus Historic Preservation Commission review in regulated areas.
• Baltimore City — CHAP review can matter for locally designated properties and districts.
• Oxford — Town historic review intersects with waterfront/Critical Area constraints.
• St. Michaels — Historic District Commission review can affect exterior ADU work.
• Chestertown — local historic review can add another approval layer.
• Hyattsville — historic-property review can sit alongside Prince George’s County zoning.
• Burkittsville — historic context is a major part of local project review.

The lesson is not that historic districts prohibit ADUs. The lesson is that the zoning entitlement and the preservation design approval can be separate decisions.

Historic status can also affect tax-credit planning

Maryland Historical Trust preservation tax-credit programs can require rehabilitation work to comply with the Secretary of the Interior’s Standards. MHT warns applicants that work begun before required review/approval can jeopardize eligibility for the credit.

If a homeowner intends to use a historic rehabilitation tax credit while adding or converting an ADU, the preservation-review timeline should be coordinated before construction starts. A building permit alone does not necessarily satisfy tax-credit program requirements.

Historic-property ADU checklist before paying for plans

1. Confirm the zoning authority. Start with the Maryland ADU Jurisdiction Finder.
2. Confirm local historic status. Ask whether the parcel is in a locally regulated district or individually designated.
3. Check Register status separately. Search Maryland Historical Trust / National Register records and ask whether the property is listed or determined eligible.
4. Ask whether a Certificate of Appropriateness or similar approval is required. Do this before final exterior design.
5. Confirm the ADU zoning path. Historic approval does not replace zoning approval.
6. Choose the least disruptive ADU type. Compare interior, attached, conversion and detached options before committing to one.
7. Document existing historic features. Photograph elevations, outbuildings, materials and site relationships before design.
8. Ask the preservation reviewer about massing, siting and visibility early. Early concept feedback can prevent expensive redraws.
9. Coordinate building code and preservation review. Egress, sprinklers and energy upgrades can affect exterior appearance.
10. If using a tax credit, obtain the program-specific approval before starting work.

What this guide does not mean

This guide does not mean that every property in a historic district is exempt from HB 1466. It also does not mean that a National Register listing by itself prohibits an ADU. Historic preservation in Maryland operates through several overlapping systems, and the exact effect depends on the property’s designation, local ordinance, private restrictions and proposed work.

The most useful homeowner question is therefore not simply “Is my property historic?” It is: which historic designation applies, who reviews the work, and which part of my ADU proposal triggers that review?

Primary sources used for this guide

• Maryland Department of Planning — HB 1466 ADU FAQ
• Maryland Real Property §2-126 — ADU private restrictions and historic-property exception
• Maryland General Assembly — HB 1236 (2026)
• Maryland Historical Trust — National Register of Historic Places
• National Park Service — Secretary of the Interior’s Standards for Rehabilitation

Maryland ADU Guide is maintained by Gijo John as an independent research publication. For local zoning rules, use the Maryland ADU Rules Tracker.