ADU rules in Baltimore County

Not adopted as of October 31, 2026

No ADU bill appeared among the 2026 council bills through Bill 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 ADU law and deferred to the county council.

Until a bill passes, the published rule is BCZR 400.4: an accessory apartment inside an owner occupied house, with a Use Permit for an interior unit. The published guide on the rule says a detached unit takes a public hearing before the Office of Administrative Hearings on top of the Use Permit.

Read on the Maryland ADU Guide page for Baltimore County (updated October 21, 2026) and the Board of Appeals coverage on Citizen Portal, October 31, 2026.

• No county ADU definition yet. The state law (Chapter 196 of 2025) sets 75 percent of the main house as the ceiling a county cannot go below once it adopts a local law.
• Accessory apartment under BCZR 400.4: inside the house, owner occupied, and under the current definition the occupants of the two units are related by blood, marriage or adoption.
• The Use Permit renews every two years.
• The accessory apartment guide quotes an earlier published cap of the lesser of one third of the floor area or 2,000 square feet; check the current Municode text with the builder before you design to it.

1. 1

   Zoning

   A Use Permit under BCZR 400.4 for an interior accessory apartment, renewed every two years. There is no ADU zoning path yet; watch the council bill list.

2. 2

   Building permit

   A residential building permit through Permits, Approvals and Inspections, filed online. A basement or attached apartment files as an alteration or addition.

3. 3

   Fire protection permit

   No fire protection permit for an accessory apartment inside an unsprinklered house. A detached unit, once allowed, gets a 13D design and its own sprinkler permit.

4. 4

   Health (well and septic lots)

   Well and septic lots in the north county (Monkton, Parkton, Freeland and the reservoir watersheds) need the Health Department to confirm the well and septic carry a second kitchen and bath before the permit issues. Public water and sewer lots inside the Urban Rural Demarcation Line skip this step.

5. 5

   Utilities

   Public water and sewer: the apartment shares the house service. Electric: a sub panel or a second BGE meter, your call with the builder.

The whole list, statewide, in the order a homeowner meets it:

No builder and no county page publishes a Baltimore County specific ADU or accessory apartment price. The ranges below are Maryland wide, from one named builder page. For a basement or attached apartment, the basement conversion and attached addition rows are the ones to read.

Source for the table:

County fees

County permit fees come from the Building Permit Fee Schedule on the Permits, Approvals and Inspections permit processing page. We did not quote dollar lines from it here:

• The fee schedule is posted under Permit Information and Forms on the county permit processing page, with category minimums rather than one countywide minimum.
• Work started before the permit adds an investigation fee on top of the permit fee.
• Ask the builder to pull the current schedule line for your permit type before you budget.

Source for the fees:

Sprinkler cost

A detached unit adds the NFPA 13D sprinkler system. On public water that runs about $1.35 to $1.60 per sprinklered square foot (Maryland Fire Sprinklers cost guide, marylandfiresprinklers.com/cost/). A well lot adds a storage tank and pump, priced on the same guide.

Statewide ranges and how the types compare:

An accessory apartment inside an unsprinklered Baltimore County house does not trigger sprinklers under the state code. The day the county allows a detached ADU, that unit is a new one family dwelling and gets an NFPA 13D system the county cannot waive (Public Safety Article 12-504). Our sister company, Maryland Fire Sprinklers, designs, permits and installs them.