ADU Guide · Verified 2026
Building an ADU in Maryland
Maryland set a statewide policy promoting ADUs and required every county and municipality with zoning authority to adopt a compliant local law by October 1, 2026. Over half the state's jurisdictions already had some form of ADU provision before the law passed, so it builds on existing rules more than it creates a single new uniform code.
Quick Facts
Statewide floors set by HB 1466 / SB 891, Chapters 196/197 of 2025, effective October 1, 2025. Your city may be more generous but cannot go below them.
The Three Types of ADU
A policy law, not a single uniform code
Rather than writing one statewide ADU code the way some states do, HB 1466 sets a policy and a deadline, requiring each county and municipality to write its own compliant local law by October 1, 2026, meaning the exact permit process still varies by jurisdiction even though the underlying protections are now statewide.
Most of the state didn't start from zero
A Task Force inventory found that 81 of 155 surveyed counties and municipalities, about 52%, already had some form of ADU provision before HB 1466 passed. The state's own guidance confirms that a jurisdiction whose existing law already meets the new requirements doesn't need to pass anything new, making a simple count of "who passed a new bill" a poor way to judge who's actually compliant.
A real local example already in place
Howard County passed its own implementing law, Council Bill 3-2026, signed February 6, 2026 and effective April 8, 2026, a real, documented case of a jurisdiction meeting the October 2026 deadline well ahead of schedule.
HOA rules get a real, specific fix
Beyond simply barring unreasonable HOA restrictions, Maryland's law requires HOAs to treat an ADU as its own separate lot for voting and assessment purposes, a specific administrative detail beyond the basic preemption most other states' HOA provisions include.
What people get wrong
The most common mistake is assuming every Maryland jurisdiction needs a brand-new ADU ordinance to comply. Over half already had qualifying rules before the law passed, and the real question is whether the existing local code meets the new statewide floor, not whether a new bill was recently signed.
From Idea to Move-In: The Timeline
Who Administers It
Counties With Their Own Rules
These Maryland counties have verified, county-specific ADU rules that add to the state baseline:
Building It Yourself? Here's What You'll Need
Planning an ADU? Tools homeowners use in the design and layout phase:
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Check Your Local Rules
Your city may allow more than the state floor
State law sets the minimum; many Maryland cities and counties are more generous. Browse the full directory of 23 counties and every city in Maryland for local rules, fees, and building department contact details.
Browse the full Maryland directory →Not sure if your project needs a building permit, a zoning approval, or both? See our guide to building permits vs. zoning approval.
Official Sources
ADU law changes frequently and local ordinances add detail. This guide is general information, not legal advice, always confirm with your local building department. Reviewed by the StateDataIndex Editorial Team · Updated September 2026.