How Rockville Handles Accessory Structures: A Practical Guide
Rockville maintains 111 local ordinances across all categories, and 5 of those deal specifically with accessory structures. Here is a breakdown of what the city actually requires, what is prohibited, and where Rockville falls on the strict-to-permissive spectrum compared to other cities.
ADU Rules
A detached Accessory Dwelling Unit in Rockville must sit on a permanent foundation and stay at or under 75% of the main house's floor area, or up to 600 square feet if that house is under 800 square feet.
Key details: Foundation: Must sit on a permanent foundation. Size, principal ≥800 sf: Up to 75% of its area. Size, principal <800 sf: Capped at 600 square feet. Also governed by: Development standards in § 25.8.1.3.
A detached ADU built without a permanent foundation, or over the 75%/600-square-foot size cap, violates § 25.6.3.6(b)(3): a municipal infraction under § 25.13.2.1(a) and § 1-9, up to $400 per day and a possible stop-work order.
ADU Rental Restrictions
Rockville, Maryland bars a landlord from holding rental licenses for both a house and its accessory apartment at once: only one of the two units on a lot may be licensed for rent at a time.
Key details: Rule: only 1 unit per lot licensed. Governs: single unit + accessory apartment. ADU standards: § 18-129 min. facilities. Citation: Rockville City Code § 18-112.
Renting out both the primary unit and the accessory apartment on the same lot without separate authorization violates the licensing scheme and can result in license denial or revocation.
This is one of the stricter rules in Rockville's municipal code. If you are unsure whether your situation complies, it is worth checking with the city before proceeding.
ADU Owner Occupancy
Owners of a Rockville one-family home with an accessory-apartment special exception must certify annually where they live and whether any part of the house is rented.
Key details: Certification: Annual, on Division of Inspection Services form. Must disclose: Owner's residence and any rental status. Inspections: At least annual, apartment and main dwelling. Fees: Owner pays certification fees.
Failing to file the annual owner-occupancy certification or refusing the Division's inspection breaches the special exception's conditions under § 5-287 (IPMC § 301.2.6), exposing the property to municipal-infraction enforcement and possible loss of the exception.
This is not one of those rules that cities tend to ignore. Rockville actively enforces its adu owner occupancy requirements.
Shed & Carport Rules
Rockville zoning treats a carport as an accessory structure: it can't share a wall or roof with the house except through a short breezeway, and a detached carport must sit in the rear yard within set height and footprint caps.
Key details: Governing section: Zoning § 25.8.1.3, accessory structures. Attachment rule: No shared wall or roof. Max footprint: 750 square feet per structure. Max height: 20 feet or roof peak. Placement: Must be located in rear yard.
A carport built onto the house without qualifying as a breezeway connection, or one exceeding the rear-yard, height, or footprint limits, is a zoning violation: a municipal infraction under § 25.13.2.1(a) and § 1-9, up to $400 per day.
Tiny Homes
Rockville's residential code adopts IRC Appendix Q in full, giving tiny houses their own building standard instead of full-size dwelling rules.
Key details: Code adopted: 2021 IRC Appendix Q. Adopting section: City Code § 5-102. Permit issuer: Inspection Services Division. Applies to: One- and two-family dwellings.
Building without a permit, or outside Appendix Q's construction requirements, can draw a stop-work order and blocks a certificate of occupancy until corrected.
The Bottom Line
Rockville is tougher than many cities when it comes to accessory structures. Out of the 5 rules covered here, 2 are rated strict. If you are a homeowner, renter, or business owner in Rockville, take the time to understand these requirements before they become a problem. Most violations come with fines, and some repeat violations can escalate.
Keep in mind that Rockville can amend these rules at any council meeting. For the most current version of any rule mentioned here, check the specific ordinance page, where we track updates as they happen.