Rockville ADU Rules 2026: 75% Size Rule, No Parking Requirement & Owner Occupancy

Rockville has its own ADU zoning rules and should not be treated as if Montgomery County’s ADU framework automatically controls properties inside the city. Rockville now allows both attached and detached accessory dwelling units as conditional uses on qualifying single-unit detached lots. The current City guidance uses a 75% size standard, requires owner occupancy, does not require ADU parking, and limits the property to one rental license.

The key planning point is jurisdiction. The City of Rockville maintains its own Zoning Ordinance, Zoning Map, permitting process and inspections. If the property is inside Rockville city limits, start with the City rather than relying on the Montgomery County ZTA 26-06 transition guide. Use our Maryland ADU Jurisdiction Finder if you are unsure which local government controls the property.

Last verified: September 13, 2026. Rockville is an incorporated municipality with its own zoning authority. This page is informational and is not legal, zoning, architectural, engineering or permitting advice.

Rockville ADU status at a glance

How large can a Rockville ADU be?

Rockville’s current ADU guidance says an accessory dwelling unit may be up to 75% of the total floor area of the main dwelling unit on the lot.

There are two notable exceptions. An attached ADU located in a basement may occupy the entire basement. The City also says a detached ADU may be as large as 600 square feet when the main dwelling has a gross floor area of 800 square feet.

This makes Rockville’s current size standard much closer to Maryland’s HB 1466 framework than the older rules still published by several counties.

Does Rockville require owner occupancy?

Yes. The property owner must occupy either the principal dwelling or the ADU for at least six months of the year. The main dwelling and ADU must also remain under common ownership.

That means Rockville’s ADU framework is not designed for an owner to separately dispose of or independently own the secondary dwelling.

Does a Rockville ADU require extra parking?

No. Rockville’s current ADU page states that ADUs are not required to provide parking spaces. This is an important difference from several Maryland counties that still publish one-space or bedroom-based ADU parking requirements.

What are the rules for detached ADUs?

A detached ADU must be located within an accessory building separate from the main dwelling. It may be created by converting an existing detached structure or by building a new accessory building on the same lot.

Rockville requires detached ADUs to be built on a foundation and to comply with the City’s accessory-building standards. The City currently lists a minimum accessory-building setback of 3 feet from a lot line, with additional setback required for taller accessory buildings.

The normal accessory-building height framework starts with a 12-foot height at the minimum setback, allows additional height with increased setback, and permits accessory buildings up to 20 feet subject to the City’s standards. The accessory building cannot exceed the height of the main dwelling.

Can a Rockville ADU be rented?

Rockville’s current guidance says only one rental license is permitted on a property. That makes the rental arrangement a separate planning issue from simply obtaining ADU approval.

Homeowners intending to rent the ADU should confirm the current rental-license requirements with the City before assuming both units can be operated as independent rentals.

What permits does a Rockville ADU need?

All existing and proposed ADUs must be permitted through Rockville’s permitting process. The City directs applicants to its MGO Connect permitting portal and separately provides a Building ADU Permit Application and Rental ADU License Application.

Rockville’s Community Planning and Development Services Department handles zoning, building-plan review and inspections. ADUs are specifically excluded from the City’s express-permit program, so homeowners should plan for standard review rather than assuming a fast-track accessory-structure permit.

Water and sewer capacity may also require City review through the Water and Sewer Authorization process where applicable.

Rockville vs. Montgomery County ADU rules

Rockville is inside Montgomery County geographically, but it maintains its own zoning authority. That means a homeowner should not automatically apply Montgomery County’s ZTA 26-06 framework, County parking rules or County licensing path to a property inside Rockville.

What Rockville homeowners should verify before spending money

1. Confirm the property is inside Rockville city limits.
2. Confirm the existing home qualifies as a single-unit detached dwelling.
3. Calculate the 75% size ceiling using the City’s current floor-area method.
4. For a detached ADU, check accessory-building setbacks, height and lot coverage.
5. Confirm owner-occupancy compliance.
6. Decide whether either dwelling will be rented and verify the one-license rule.
7. Check water/sewer capacity and other site-specific reviews.
8. Apply through the City’s normal ADU permit process rather than the express-permit program.

Primary sources used for this Rockville guide

• City of Rockville — Accessory Building, Structure, and Dwelling Unit Regulations
• City of Rockville — FY2025 Rockville 2040 Comprehensive Plan Annual Report
• Rockville Community Planning and Development Services Department
• City of Rockville — Express Permit Program
• Maryland Department of Planning — HB 1466 ADU FAQ

For statewide comparison, use the Maryland County & City ADU Rules Tracker. Maryland ADU Guide is maintained by Gijo John as an independent research publication.