Maryland ADU
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Rules tracker

Maryland ADU rules, the state law and every county bill

In 2025 the General Assembly told every Maryland county and municipality with zoning authority to adopt a local ADU law by October 1, 2026. Some counties already had one. Some passed theirs this year. Two of the seven we cover had not finished when we last checked.

This page is the state law in plain words, then one row per county with the bill number and where it stands. Each row links to the county page with the full rule, the permit path and the cost.

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The state law

Chapter 196 of 2025 (SB 891, cross filed HB 1466)

  • Deadline: every county and municipality with zoning authority adopts a local ADU law by October 1, 2026.
  • Size: an ADU is not greater than 75 percent of the size of, and subordinate in use to, the primary single family detached dwelling. A county can set a smaller cap, and Anne Arundel does.
  • Fees: no impact fee on a unit under 750 square feet.
  • Parking: no parking mandate within 0.75 mile of transit.
  • The act changes zoning, not the building code. It says nothing about fire sprinklers, so the sprinkler rule for a detached unit stays exactly where the state building code put it.

What that means for a detached unit:

ADU fire sprinklers in Maryland
County by county

Where each county stands

Read October 31, 2026 from the county council and permit pages named at the bottom. Tap a county for its page.

  • Allowed since 2023
    Bill 6-23, Bill 71-26 pending

    Anne Arundel County

    • Detached ADUs allowed since Bill 6-23 in April 2023.
    • Cap: the lesser of 800 square feet or 50 percent of the house, tighter than the state 75 percent.
    • Bill 71-26 (introduced September 8, 2026, hearings October 5 and October 19) still carries the 800 square foot definition, so the county has not matched the state cap yet.
    Anne Arundel County ADU page
  • Allowed since April 2026
    CB 3-2026 (ZRA 218)

    Howard County

    • Signed February 6, 2026, effective April 8, 2026.
    • Attached, detached or inside the house. Cap 75 percent of the principal footprint, two bedrooms, owner occupied.
    • The county webinar says the bill leaves the building code, and so the sprinkler rule, alone.
    Howard County ADU page
  • Not adopted
    No ADU bill as of October 31, 2026

    Baltimore County

    • No ADU bill among the 2026 council bills through 88-26. Bill 20-26, enacted April 15, 2026, is an impact fee bill, not an ADU bill.
    • The Board of Appeals declined to interpret the state law and deferred to the council.
    • Today the zoning regulations (BCZR 400.4) allow accessory apartments inside the house only.
    Baltimore County ADU page
  • Allowed by right
    ZTA 19-01 (2019)

    Montgomery County

    • ADUs by right since 2019 under ZTA 19-01.
    • The Department of Permitting Services keeps a guidelines sheet for ADUs, revised December 11, 2025.
    • A detached ADU gets a 13D sprinkler system and a fire protection permit from DPS; an attached unit sprinklers only if the house already does.
    Montgomery County ADU page
  • Bills pending
    CB-074-2026 and CB-092-2026

    Prince George's County

    • CB-074-2026 (definitions and zones) passed committee 3 to 0 on September 8, 2026.
    • CB-092-2026 (the regulations) had its hearing October 26, 2026 and is set for second reading.
    • On October 5 the county said it will ask the state for a deadline extension. DPIE Adoption Bulletin 2026-03 (October 14, 2026) cites CB-74 and applies the residential code to ADUs.
    Prince George's County ADU page
  • Allowed
    Code 1-19 (Bills 18-16 and 20-10)

    Frederick County

    • Detached ADUs, or a unit inside an accessory structure, under county code 1-19.
    • The residential permit sheet (revised September 1, 2025) requires a sprinkler application for every ADU in or as an accessory structure on a single family lot.
    Frederick County ADU page
  • Allowed since July 2026
    Bill 2026-06 (ZTA 25-189)

    Charles County

    • Passed unanimously after the July 7, 2026 hearing.
    • Any zone that allows single family detached, one unit per lot, 75 percent of the primary house, two bedrooms.
    Charles County ADU page
After the rule

What to read next

Once you know your county allows the unit, the next three questions are the type, the permits and the money.

Detached vs attached ADUADU permit checklistADU cost in Maryland
Get matched

A licensed builder who works under your county's bill

Send the address and the kind of unit. We check it against the county rule and the sprinkler question, then connect you with a licensed Maryland builder who already does ADUs there. We do not build the unit. We make the match.

14 builders on the list, seven counties, one person reads every form the same day.

Sources read for this page

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