ADUs are allowed in RockvilleTypes:DetachedInternal
Types:DetachedInternal
Accessory Dwelling Unit (ADU) Rules for Rockville, MD
Is your property eligible for an ADU?
# of Properties
15,320
Owner-occupied
83%
Zoning districts
32
Avg Home Value
$718,045
Median Lot Size
0.17 acres
Avg Income
$167,919
Residential Types:
15,320 housing units
Single Family
72%
Apts (4+ units)
1%
Other
27%
Zoning Districts:
16,936 parcels · 32 districts
R-60
36%(6,135)
PD
32%(5,407)
R-90
16%(2,637)
MXCD
3%(538)
Other
13%(2,219)
ADU Rules
What can you build in Rockville, MD?
Rockville, MD follows state and local rules for Accessory Dwelling Units. Here is a concise overview of the local rules.
Eligibility
- –Internal / Attached ADU: Conditional Use Permit
- –Detached ADU: By Right
Interior / Attached ADU Size Limits
- –Maximum size of 50% of the primary dwelling’s total floor area.
Detached ADU Size Limits
- –Maximum size is the lesser of 750 sq ft or 50% of the main dwelling’s gross floor area.
Max Units
- –1 ADU per lot total in single-unit detached zones (either 1 attached OR 1 detached; detached prohibited if an attached ADU exists)
- –0 ADU per lot in single-unit semi-detached/duplex (R-40)
Owner Occupancy
- –Owner must occupy either the attached ADU or the main dwelling
Parking
- –Attached ADU: min 2 spaces/lot, or 1 space if within 0.7 miles of a Metro station; Detached ADU: no minimum stated. Exceptions: chief may allow no off-street spaces if on-street capacity exists on the same block; or if attached ADU is created entirely within the existing main building with no exterior modifications, no off-street parking is required.
Rental Restrictions
- –Detached ADU: only one rental license per property; attached ADU: owner must occupy either the ADU or main dwelling, so both units cannot be rented.
ADU State Law
What can you build in Maryland?
- –Local-law mandate: By Oct 1, 2026, each legislative body must adopt a local law authorizing ADUs under this section.
- –Local zoning mostly remains: The subtitle generally does not alter local zoning power except as provided, but locals must establish policies that further the subtitle's intent.
- –Definition-based size cap: An ADU must be ≤ 75% of the size of the primary SF detached dwelling and subordinate in use; ADUs may be detached or attached.
- –Density/growth limits: ADUs must be excluded from density calculations and from measures limiting residential growth that pertain to the lot/parcel/tract.
- –Setbacks: Local law cannot set side/rear setbacks that exceed existing accessory-structure setbacks.
- –Parking: If a jurisdiction adds off-street parking requirements, it must consider specified factors and provide a waiver process, and must complete a parking study before adopting such requirements.
- –Alley access option: Local law may prohibit converting an accessory structure to an ADU if only vehicular access is from an alley.
- –Codes/adequate facilities: Local law must provide for ADU construction meeting public health/safety/welfare standards, including building codes and adequate public facilities provisions.
What's allowed on your lot?
These are the municipality-wide rules. What's allowed on a specific property also depends on state laws, setbacks, floor area ratio, lot coverage, environmental constraints, topography, and other property-specific factors. Search your address on FutureLot to see what's allowed on your property.
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ADU rules in other Maryland municipalities
Rules change at the town line. Check the municipality your property is actually in.
Montgomery County