ADU rules in Anne Arundel County

In force since April 2023

Bill 6-23 passed in April 2023 and allows a detached accessory dwelling unit on a single family lot.

Bill 71-26, sponsored by Volke, was introduced on September 8, 2026, with hearings on October 5 and October 19. It still defines an ADU at 800 square feet, so the county has not moved to the state 75 percent cap. It was pending when we checked on October 31, 2026.

Read on the county council pages for Bill 6-23 and Bill 71-26, October 31, 2026.

• Size: the lesser of 800 square feet or 50 percent of the main house.
• One ADU per single family lot, under Bill 6-23.
• The state cap (75 percent of the main house, Chapter 196 of 2025) is higher than the county cap; until the council changes the county definition, 800 square feet is the number to design to.
• Large additions have a separate county test: an addition at 50 percent of the house hits the county sprinkler test.

1. 1

   Zoning

   The ADU has to meet the Bill 6-23 definition: the 800 square foot or 50 percent cap, one per lot, on a single family lot. Zoning review runs through the Office of Planning and Zoning before the building permit.

2. 2

   Building permit

   A building permit through Inspections and Permits. The county points applicants to its LUN online system for the application and the fee estimate. A detached unit files as new construction; a conversion files as an addition or alteration.

3. 3

   Fire protection permit

   A detached ADU needs a 13D sprinkler design and its own sprinkler permit. An attached or basement unit in an unsprinklered house below the addition test does not.

4. 4

   Health (well and septic lots)

   Well and septic lots, common on the Broadneck, Mayo and Shady Side peninsulas and in south county, need the Health Department to confirm the well and the septic system can carry a second unit before the permit issues.

5. 5

   Utilities

   Public water lots: a tap or a new service sized for sprinkler flow on a detached unit. Well lots: a storage tank and booster pump at the unit. Electric is a sub panel or a second BGE meter.

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

No builder publishes an Anne Arundel County specific ADU price. The ranges below are Maryland wide, from one named builder page. The 800 square foot cap keeps the detached number toward the lower end; a well lot pushes it back up with the tank, pump and health review.

Source for the table:

County fees

County permit fees on top of construction, from the Inspections and Permits fee page (effective October 1, 2024):

• Building permit: $86 minimum, $242 at an estimated cost of $25,000, then $242 plus 1 percent of the estimated cost above $25,000.
• A $43 application fee on every building permit, non refundable.
• Plumbing permit for a new detached single family dwelling: $173. Electrical permit, 200 amps or less: $147.
• Additions and alterations: electrical $95 without a service change; plumbing $51 for the first fixture and $8 for each additional fixture.

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:

Every detached ADU in Anne Arundel County gets an NFPA 13D sprinkler system. The county cannot weaken the state rule (Public Safety Article 12-504), and on a well lot the system needs its own tank and pump. Our sister company, Maryland Fire Sprinklers, designs, permits and installs them.