The ADU permit path in Maryland, in the order you meet it

1. 1

   Zoning

   The county planning and zoning office

   The unit has to fit the county ADU bill before anything else moves: the size cap against the main house, the bedroom count, owner occupancy where the county asks for it, one unit per lot. Where the county has no bill yet (Baltimore County, Prince George’s as of October 31, 2026) this is the step that stops.

   Have ready

   • The address and the lot size
   • Main house square footage, since the cap is a share of it
   • Which type: detached, attached or inside the house
2. 2

   Building permit

   The county permits office (Inspections, Licenses and Permits in Howard; Inspections and Permits in Anne Arundel; DPS in Montgomery; DPIE in Prince George’s)

   A detached unit files as new residential construction with its own plan set. An attached or basement unit files as an addition or alteration. The fee follows the filing type, and the county fee schedule is public.

   Have ready

   • Stamped plans from the builder or designer
   • A site plan with setbacks
   • The estimated construction cost, since several counties price the permit off it
3. 3

   Fire protection permit

   The county fire marshal or the permits office, depending on the county

   A detached ADU is a new dwelling under the state building code and gets an NFPA 13D sprinkler design and its own permit. Montgomery County issues a fire protection permit for it; Frederick County requires a sprinkler application for every ADU in or as an accessory structure. An attached or basement unit inside an unsprinklered house normally skips this step.

   Our sister company, Maryland Fire Sprinklers, designs and permits the system.

   Have ready

   • The 13D design from the sprinkler contractor
   • A flow test on public water, or the tank and pump sizing on a well
4. 4

   Health (well and septic lots)

   The county health department

   On a well or septic lot the health department confirms the well yield and the septic capacity can carry a second kitchen and bath before the building permit issues. Public water and sewer lots skip this step. Common on the Anne Arundel peninsulas, in south county, and across the rural parts of Frederick and Charles.

   Have ready

   • The septic permit or as built if you have it
   • The well completion report
   • The bedroom count for the whole property, since septic sizing runs on bedrooms
5. 5

   Utilities

   The water and sewer utility, the electric utility for your county, and the permits office for the trade permits

   Public water: a tap off the house line or a new service, sized for sprinkler flow on a detached unit. Well: a storage tank and booster pump at the unit. Electric: a sub panel or a second meter. Each one is a trade permit with its own inspection.

   Have ready

   • The sprinkler flow demand, so the tap is sized once
   • The panel schedule for the house
   • A decision on one meter or two

• Public water and sewer lot, basement or attached unit in an unsprinklered house: zoning, building, utilities. Three steps.
• Public water lot, detached unit: zoning, building, fire protection, utilities. Four steps, and the water tap is sized for the sprinklers.
• Well and septic lot, detached unit: all five, with the sprinkler tank and pump sized next to the well review.

Which unit type meets which steps, side by side: