What the law is
In 2025, Maryland passed Chapter 197 of the 2025 Laws of Maryland — the bills were HB 1466 and SB 891, titled "Land Use and Real Property – Accessory Dwelling Units – Requirements and Prohibitions." The Governor approved it April 22, 2025 (Senate 47–0, House 138–1), it took effect October 1, 2025, and it created a new Subtitle 5 on Accessory Dwelling Units (§§4-501–4-507) in the Land Use Article. It applies to charter counties and Baltimore City.
Sources: Chapter 197 of the 2025 Laws of Maryland (mgaleg.maryland.gov).
By-right approval: what that actually means
"By right" does not mean "no permits." It means the county must judge your application against clear, written, measurable rules — and nothing else. For a complete ADU zoning application, the county must approve or deny within 90 days, decided "in a ministerial manner" — no discretionary hearing, no judgment call. Subjective tests like "neighborhood compatibility," aesthetics, or "adverse impacts" are explicitly banned; only objective criteria (size, setbacks, height, utility connections) are allowed.
Sources: Chapter 197, §§4-504(C)(5), 4-504(D)(5), 4-505.
The state guardrails (every county must follow these)
Size: an ADU may be at most 75% of the primary home's size, and must be smaller than the primary. No minimum size is set by the state.
Parking: within 0.75 mile of mass transit, the county may require no new off-street parking. Beyond that, at most one space. More requires a parking study plus a waiver.
Fees: no development impact fee or building excise tax on ADUs under 750 square feet. At 750+ square feet, fees must be proportional to the primary home's size. A utility may not demand a separate water/sewer connection where the existing one suffices, may not charge a connection fee for tying in, and you may use a shared water meter.
Sources: Chapter 197, §§4-501, 4-504(C)(1), 4-504(D)(4), 4-506, 4-507.
HOAs: what the law says
HOA and deed restrictions may not impose an unreasonable limitation on developing or renting an ADU — defined as anything that significantly increases the cost or effectively prohibits ADUs. But HOAs may still ban short-term rental of the ADU, and may treat the ADU as a separate lot for voting and assessments. Historic properties are carved out. Our HOAs and ADUs guide goes deeper.
Sources: Real Property §2-126 (Chapter 197); RP §11B-111.11, §11B-117(a)(2)(II).
What the law does NOT do
The state set a floor, not a ceiling. Counties keep authority over construction standards, design rules, placement, and administration within the guardrails. Septic and well constraints still apply — the law yields where safe-drinking-water limits or sewage health risks prohibit new dwelling units. Local fees at 750+ square feet, local timelines, and local size caps (within the 75% ceiling) are still the county's call. And every county had until October 1, 2026 to adopt its implementing rules — which is why some counties are voting right now. See Charles County's rules, Prince George's County's rules, and Montgomery County's rules.
Sources: Chapter 197, §§4-504(A)(1), 4-504(B)(2).
Check it yourself
The full chapter text is public at mgaleg.maryland.gov — search Chapter 197 of the 2025 Laws of Maryland. For what it means on your lot: call (240) 222-5082 and we will walk it free.