Accessory Structures in Charles County, MD (2026)
4 rules for unincorporated Charles County, Maryland.
Verified from official government sources
ADU Rules
Charles County allows one accessory apartment per single-family home, in the main house or in a detached accessory building, capped at 300 to 50% of the host structure's floor area. Accessory buildings are further limited to two bedrooms and no street-facing entrance.
Charles County Accessory Apartment (ADU) Rules
Some RestrictionsCharles County, MD Zoning Ordinance § 297-212(23)(B)-(C), Use 3.01.700
3.01.700 Single-family detached residential: primary residence with accessory apartment. This use is permitted with conditions in the HVC, HVG, HVR, AC, RC, RR, RV, RL, RM, RH, RO, MX, TOD, WCD, CER, CMR and CRR Zones... B. Apartment size. The minimum floor area for an accessory apartment within a principal dwelling shall be 300 square feet, but in no case shall it exceed 50% of the gross floor...
Shed & Carport Rules
A shed or other accessory structure in Charles County's agricultural, rural, or residential zones needs a zoning permit, cannot exceed 50% of the principal structure's gross floor area or 1,000 square feet (whichever is greater), and must sit at least six feet from side or rear lot lines.
Charles County Shed and Accessory Structure Rules
Some RestrictionsCharles County Code § 297-29B, B(1), B(5)
Prior to the commencement of any accessory use or the construction of any accessory structure with an agricultural, rural, or residential zone, a zoning permit must be obtained... In the residential zones and on lots less than three acres in agricultural and rural zones, the area of a single accessory use or structure shall not exceed 50% of the gross floor area of the principal use or structur...
Garage Conversions
Converting a garage or other accessory building into a living space in Charles County requires county Health Department sign-off on water and sewer service before a zoning permit can issue, under the accessory apartment provisions of Use 3.01.700.
Charles County Garage-to-Apartment Conversion Rules
Some RestrictionsCharles County, MD Zoning Ordinance § 297-212(23)(E), Use 3.01.700
A. An accessory apartment may be located either in the principal dwelling unit or in an accessory building... E. Water and sewerage service. Prior to the issuance of a zoning permit for the establishment of an accessory apartment in or existing residential structure or the conversion of an existing accessory building to an accessory apartment use, approval of the proposed method of water supply...
Tiny Homes
Charles County wrote Appendix AO, Tiny Houses, of the 2021 International Residential Code directly into its local Building Code, and separately exempts one-story detached accessory structures under 200 square feet from a building permit if they are not used for vehicle storage.
Charles County Tiny House Code Adoption
Some RestrictionsCharles County Code § 224-1.2(2)
IRC Section R102.5, replace in its entirety with: The following appendices of the 2021 IRC are hereby adopted into the Charles County Building Code. (AA) Sizing and Capacities of Gas Piping, ... (AE) Manufactured Housing Used as Dwellings, ... (AM) Home Day Care—R-3 Occupancy, (AN) Venting Methods, and (AO) Tiny Houses.
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