Can I build an ADU in Maryland?

Statewide policy changed in 2025: the Accessory Dwelling Units Act of 2025 requires every Maryland county and municipality to permit at least one accessory dwelling unit on a lot with an existing single-family home. The law took effect October 1, 2025, and local governments must have compliant ordinances in place by October 1, 2026, so specific standards are still being finalized locally.

Who handles zoning in Montgomery and Prince George's counties?

Both counties use the Maryland-National Capital Park and Planning Commission (M-NCPPC), a bi-county state agency created in 1927, to administer zoning and planning instead of a standard county planning department. Prince George's County's rewritten zoning ordinance, approved in 2018, took effect in April 2022 after delays; Montgomery County has separately overhauled its own code.

Is Maryland a home-rule state?

Maryland's larger counties are generally charter counties operating under Article XI-A of the Maryland Constitution and the Express Powers Act, giving their county councils direct authority to enact and amend zoning law. The remaining code counties rely more directly on state public local laws, and the statewide enabling framework for both is the Land Use Article of the Maryland Code.

How is Baltimore City zoning different from the rest of Maryland?

Baltimore City replaced its 1971 zoning code in 2017 with TransForm Baltimore, a comprehensive rewrite meant to support more walkable, mixed-use, transit-oriented development. As an independent city that is not part of any county, Baltimore administers its own zoning code entirely separate from Maryland's county-based system.

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Maryland zoning: how it works and what you can build

Maryland splits zoning almost entirely between home-rule charter counties and a handful of code counties, with the unique bi-county Maryland-National Capital Park and Planning Commission running zoning for Montgomery and Prince George's counties — on top of a new 2025 statewide ADU mandate local governments must implement by October 2026.

How zoning works in Maryland

Zoning authority in Maryland rests overwhelmingly with its 23 counties and Baltimore City rather than the state, under the Land Use Article of the Maryland Code — the 2012 recodification of the former Article 66B — which is the statewide enabling framework for both planning and zoning. Charter counties operate under Article XI-A of the Maryland Constitution and the Express Powers Act, giving their county councils broad home-rule authority to enact and amend local zoning law directly; the remaining code counties rely more directly on state public local laws.

The most distinctive feature of Maryland zoning is the Maryland-National Capital Park and Planning Commission (M-NCPPC), a bi-county state agency created in 1927 that performs planning, zoning administration, and park operations for both Montgomery and Prince George's counties, effectively substituting for a normal county planning department across the DC suburbs. Prince George's County's Zoning Ordinance rewrite, approved by the County Council in 2018, took effect in April 2022 after implementation delays, replacing its legacy Euclidean code with a streamlined district structure; Montgomery County has separately overhauled its own zoning code.

Baltimore City replaced its 1971 zoning code in 2017 with TransForm Baltimore, a comprehensive rewrite intended to legalize more walkable, mixed-use development. On housing supply generally, the General Assembly passed the Accessory Dwelling Units Act of 2025, a statewide mandate requiring every county and municipality to permit at least one ADU on lots with an existing single-family home; it took effect October 1, 2025, with local implementing ordinances due by October 1, 2026 — one of the most consequential statewide zoning preemptions in Maryland's history.

Who holds the zoning power

Land-use authority in Maryland is delegated by statute, not assumed — these are the acts a zoning ordinance in Maryland has to trace back to.

Land Use Article Md. Code, Land Use Article (recodified 2012 from Article 66B): Statewide enabling framework for county and municipal planning and zoning.
Home rule for charter counties Md. Const. art. XI-A; Express Powers Act: Grants charter counties broad home-rule legislative power, including zoning, exercised directly by the county council.
Accessory Dwelling Units Act of 2025 2025 Md. Laws: Statewide mandate requiring local governments to permit ADUs on single-family lots, effective Oct. 1, 2025, with local ordinances due by Oct. 1, 2026.

Major cities and their codes

The enabling act sets the ceiling; the municipal code is what a project is actually reviewed against. The 7 largest Maryland jurisdictions and the codes they administer:

Maryland — municipal zoning codes
City	Zoning code
Baltimore City	Baltimore City Zoning Code ("TransForm Baltimore") Rewrote the city's 1971 zoning code in 2017 to support mixed-use, transit-oriented, walkable development.
Montgomery County (Rockville, Bethesda, Silver Spring, Germantown)	Montgomery County Zoning Ordinance (administered by M-NCPPC) Covers unincorporated Montgomery County, including large unincorporated centers like Silver Spring and Germantown; several incorporated cities inside the county keep their own separate codes.
Prince George's County (Bowie, Laurel, College Park)	Prince George's County Zoning Ordinance (administered by M-NCPPC) Council-approved rewrite in 2018 took effect April 2022 after delays, cutting the number of zoning districts and modernizing development standards.
Frederick	City of Frederick Zoning Ordinance One of the fastest-growing incorporated cities in Maryland outside the DC/Baltimore core.
Rockville	Rockville Zoning Ordinance Incorporated city inside Montgomery County that maintains its own zoning code independent of M-NCPPC.
Gaithersburg	Gaithersburg Zoning Ordinance Incorporated city inside Montgomery County with its own independent zoning code and active transit-oriented redevelopment.
Annapolis	Annapolis Zoning Ordinance State capital; historic-district design review is layered on top of base zoning downtown.

Recent reforms

State-level changes override or preempt what a local ordinance says — these are the Maryland reforms that move the numbers on a real site.

2025 Accessory Dwelling Units Act of 2025 Statewide mandate requiring every county and municipality to permit at least one ADU on single-family lots; local ordinances due by October 2026.
2022 Prince George's County Zoning Ordinance rewrite New zoning ordinance, approved by the County Council in 2018, took effect April 2022 after implementation delays, replacing the county's legacy Euclidean zoning code with a modernized, streamlined district structure.
2017 TransForm Baltimore Baltimore City's first full zoning code rewrite since 1971, aimed at legalizing more walkable, mixed-use, transit-oriented development.

Parcel & GIS data

Maryland maintains one of the more mature statewide GIS systems among these states, MD iMap, which aggregates parcel, zoning, and planning layers across most counties.

Parcel-level feasibility in Maryland waits on that data being ingested and the ordinances encoded — the waitlist below is what sets the order.

Zoning by city

The statute sets who may zone; the city's own code sets what you can build. One guide per Maryland city below, explaining the district codes that appear on its zoning map — 91 district codes across Maryland so far.

Maryland zoning — common questions

Can I build an ADU in Maryland?: Statewide policy changed in 2025: the Accessory Dwelling Units Act of 2025 requires every Maryland county and municipality to permit at least one accessory dwelling unit on a lot with an existing single-family home. The law took effect October 1, 2025, and local governments must have compliant ordinances in place by October 1, 2026, so specific standards are still being finalized locally.
Who handles zoning in Montgomery and Prince George's counties?: Both counties use the Maryland-National Capital Park and Planning Commission (M-NCPPC), a bi-county state agency created in 1927, to administer zoning and planning instead of a standard county planning department. Prince George's County's rewritten zoning ordinance, approved in 2018, took effect in April 2022 after delays; Montgomery County has separately overhauled its own code.
Is Maryland a home-rule state?: Maryland's larger counties are generally charter counties operating under Article XI-A of the Maryland Constitution and the Express Powers Act, giving their county councils direct authority to enact and amend zoning law. The remaining code counties rely more directly on state public local laws, and the statewide enabling framework for both is the Land Use Article of the Maryland Code.
How is Baltimore City zoning different from the rest of Maryland?: Baltimore City replaced its 1971 zoning code in 2017 with TransForm Baltimore, a comprehensive rewrite meant to support more walkable, mixed-use, transit-oriented development. As an independent city that is not part of any county, Baltimore administers its own zoning code entirely separate from Maryland's county-based system.

Working in Maryland? Get on the list.

The parcel layer lands in the order demand does. Illinois went first because that's where the deals were; the next state is decided by who tells us what they're trying to underwrite. Tell us where you're building and what you wanted to run — you'll hear from us when Maryland opens, and sooner if we need a test parcel.

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Want to see the finished shape of this work? Illinois is live at parcel level — Illinois zoning and the 53-district Chicago reference.

Maryland zoning summaries on this page are provided for information, not legal advice. Confirm every project against the current adopted code for the jurisdiction and the statute as amended.