The state law behind all of this
In 2025, Maryland passed Chapter 197 of the Laws of Maryland (HB 1466 / SB 891), "Land Use and Real Property – Accessory Dwelling Units – Requirements and Prohibitions." Approved April 22, 2025, effective October 1, 2025, it created Land Use Article §§4-501–4-507 and set guardrails every county must follow:
- Counties had to adopt local ADU rules by October 1, 2026 (§4-504(a)(1)).
- An ADU must be smaller than the main home and no bigger than 75% of its size (§§4-501, 4-504(c)(1)).
- Complete applications get a decision within 90 days, decided ministerially — no discretionary hearing (§4-505).
- Counties may not deny based on subjective tests like "neighborhood compatibility," design, or aesthetics (§4-504(d)(5)).
- No impact fees or excise tax on ADUs under 750 square feet; above that, fees must be proportional to the main home (§4-506).
- Within 0.75 mile of mass transit, no new parking may be required; beyond that, at most one space (§4-504(d)(4)).
- Utilities may not force a separate water/sewer connection or charge a connection fee where the existing one suffices — shared meters allowed (§4-507).
- HOAs and deed restrictions may not unreasonably block ADUs — "unreasonable" means significantly raising the cost or effectively prohibiting them; short-term-rental bans are still allowed (Real Property §2-126).
One thing that did not become law: the 2026 "Generational Housing Act" (HB 1538), which would have required counties to allow two ADUs per lot, did not pass. The state law sets a floor of one ADU per eligible lot — not two.
Sources: Chapter 197 enrolled text (mgaleg.maryland.gov); MACo 2026 end-of-session wrap-up (HB 1538 status). Our plain-English guide to Maryland's ADU law goes deeper.
Charles County
Status: enacted. Bill 2026-06 / ZTA #25-189, "Flexibility for Accessory Dwelling Units," passed unanimously on July 7, 2026 and is codified in the county code at §3.01.700 ("primary residence with accessory apartment"). No further votes pending — the law is in effect.
What the enacted law provides: attached or detached ADUs permitted with conditions in any district where single-family detached homes are allowed. On lots under 3 acres, up to 1,000 square feet or 75% of the main home's floor area, whichever is smaller; on 3+ acres, up to 75% with no absolute cap. Maximum 2 bedrooms, one ADU per lot, and no off-street parking required.
Official resources:County meeting agenda, July 7, 2026 (charlescountymd.gov) · Codified text, §3.01.700 (ecode360.com)
Permit office: Department of Planning & Growth Management — 301-645-0692.
Our full breakdown: Charles County ADU rules, explained.
Sources: Bill 2026-06 passage (Star 98.3 FM, July 7, 2026); enacted bill text (§§3.01.700.A–I).
Prince George's County
Status: enacted per county records.CB-074-2026 — the county's ADU bill — shows as enacted September 29, 2026 in the county's legislation tracker, with an effective date of November 16, 2026 (45 days after adoption). A companion bill, CB-092-2026 (short-term rental rules, rental requirements, tree canopy, septic), was at Second Reading as of October 5, 2026 — not enacted. A bridge resolution (CR-095-2026) covers the gap between the October 1 state deadline and the law's effective date.
What the bill package provides (per the published committee drafts): ADUs by right on lots with single-family detached homes; size capped at 75% of the principal house; detached ADUs no taller than 22 feet; owner-occupancy required; maximum 4 persons per ADU; short-term rentals banned; and a compliance pathway for pre-existing unpermitted units. Re-check the enacted text before you act on any of it.
Official resources:County Council legislation tracker (Legistar)
Our full breakdown: Prince George's County ADU rules.
Sources: County Council Legistar (CB-074-2026 status); Coalition for Smarter Growth testimony, Sept 2026; PHED committee summaries, Sept 2026.
Montgomery County
Status: current law + pending changes. Montgomery County has allowed ADUs as a limited use (no conditional-use hearing) since 2019, under County Code Chapter 59, Section 3.3.3. Attached ADUs are allowed in all residential zones; so are detached ADUs. A Class 3 ADU license from the Department of Housing and Community Affairs (DHCA) is required, and owner-occupancy currently applies — either the main house or the ADU must be the owner's primary residence.
Pending:ZTA 26-06 would rewrite the ADU standards to align with state Chapter 197 (a vote was expected September 15, 2026 — outcome unconfirmed). Bill 41-26 ("Landlord-Tenant Relations – Licensing Procedures and Fees – Accessory Dwelling Unit," lead sponsors Councilmember Friedson and Council President Fani-González, introduced September 15, 2026) would eliminate the owner-occupancy requirement entirely and waive all building permit fees (building, mechanical, electrical, fire, use-and-occupancy) plus the annual DHCA license fee and other application fees for ADUs whose owners sign a DHCA agreement to charge rent affordable to households earning 65% or less of area median income for at least 10 consecutive years. The Planning Board signaled support on October 1, 2026 — Planning Director Jason Sartori: "the owner-occupancy requirement is a significant obstacle to creating new ADUs." Public hearing October 6, 2026 at 1:30 p.m. (PHP Committee worksession October 26). It is not law — until it passes, owner-occupancy stands.
Official resources:DHCA Class 3 ADU license page (montgomerycountymd.gov) · DPS ADU guidelines (PDF) · Planning Board backs Bill 41-26 (Bethesda Magazine, Oct 2, 2026)
Our full breakdown: Montgomery County ADU rules.
Sources: Montgomery County Code Ch. 59 §3.3.3; DHCA Class 3 ADU info sheet; DPS ADU guidelines; Bill 41-26 introduction packet, County Council (Sept 15, 2026); Bethesda Magazine, Oct 2, 2026.
St. Mary's County
Status: allowed under existing law; state-alignment update in progress. ADUs are already permitted under the county zoning ordinance at §51.3.108. The county has been working through amendments — including an owner-occupancy requirement for newly built ADUs — to align with the state law. Because the amendment process was still moving, confirm the current ordinance text with the county before you act.
Official resource: St. Mary's County Department of Land Use and Growth Management — confirm the current ADU ordinance text and permit process with the county directly before spending money on plans.
Sources: St. Mary's County zoning ordinance §51.3.108; Board of County Commissioners first-reading action on the ADU zoning text amendment.
Baltimore County
Status: existing permit program; state-alignment required by October 1, 2026. Baltimore County runs an Accessory Apartment Use Permit through its Zoning Review office (a $100 use permit with a recorded Declaration of Understanding). The county zoning regulations address accessory apartments at §400.4: per the county's 2024 legislation, an apartment in an accessory building is capped at 1,200 square feet on lots of one acre or more, 800 square feet on smaller lots, with owner-occupancy conditions.
The county was required to adopt state-compliant ADU rules by October 1, 2026 — verify the current published text, since the 2024 rules above predate the state alignment.
Official resource:Zoning Use Permit — Accessory Apartment (baltimorecountymd.gov).
Sources: Baltimore County Zoning Use Permit page; Baltimore County Bill 7-23 (2024) §400.4 text.
Anne Arundel County
Status: allowed; 2023 zoning update. Anne Arundel County updated its zoning code in 2023 to make ADUs easier across most residential districts. Reported rules: one ADU per lot (attached, internal, or detached); detached ADUs capped at the smaller of 800 square feet or 50% of the primary home's living area; separate entrance required; no additional parking required. These are reported summaries — confirm with the county's Office of Planning and Zoning, since the state-alignment update may have changed them.
Official resource: Anne Arundel County Office of Planning and Zoning — confirm current ADU standards with the county directly.
Sources: reported county zoning summaries (2023 update); confirm against current published code before acting.
Before you spend a dollar
County rules change — sometimes mid-project. The pattern that never fails: check the current published rules for your exact address before you pay for drawings. That is exactly what our free lot walk does — we check zoning, setbacks, and the county's current ADU rules for your property, then give you a written price.