ADUs are allowed in Mount AiryTypes:Internal
Types:Internal
Accessory Dwelling Unit (ADU) Rules for Mount Airy, MD
Is your property eligible for an ADU?
# of Properties
3,389
Owner-occupied
88%
Zoning districts
14
Avg Home Value
$499,062
Median Lot Size
0.29 acres
Avg Income
$150,990
Residential Types:
3,389 housing units
Single Family
6%
Other
94%
Zoning Districts:
4,104 parcels · 14 districts
RE
43%(1,752)
R2
21%(867)
R7
16%(661)
R3
9%(378)
Other
11%(446)
ADU Rules
What can you build in Mount Airy, MD?
Mount Airy, MD follows state and local rules for Accessory Dwelling Units. Here is a concise overview of the local rules.
Eligibility
- –Internal / Attached ADU: Special Permit
- –Detached ADU: Not permitted
Interior / Attached ADU Size Limits
- –Maximum size for a family apartment is 30% of the principal dwelling’s gross floor area
Max Units
- –Accessory apartment: up to 1 unit per 900 sq ft gross floor area; existing structure must be pre-1951 and have at least 1,800 sq ft, and be owner-occupied.
- –Family apartment: 1 per dwelling.
Owner Occupancy
- –Owner-occupancy is required; at least one owner must reside in principal dwelling.
Parking
- –Accessory apartment: no minimum stated; off-street parking per zoning requirements for each dwelling unit. Family apartment: 2 additional off-street spaces beyond dwelling requirements. Maximum not specified.
Rental Restrictions
- –Internal family ADU: occupancy limited to related persons; owner must reside; if owner is absent >60 days, use must cease; annual affidavit required.
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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Is your property eligible for an ADU?
ADU rules in other Maryland municipalities
Rules change at the town line. Check the municipality your property is actually in.
Frederick County