Build Your ADU in the City of Rockville, MD
Makara ADU designs, permits and builds accessory dwelling units to the City of Rockville’s rules, and builds nothing else.
- ADU max size
- Up to 75% of the main house's floor area · a detached ADU may be 600 sq ft when the house is under 800 sq ft · a basement ADU may fill the basement
- Minimum lot size
- No minimum
- Owner occupancy
- Required
- Off-street parking
- No parking spaces required for an ADU
- Allowed by
- Right, in all residential zones
- Rules current as of
- 2026-08-01
- Licensed & Insured in Maryland (MHIC 151479)
- City of Rockville ADU Specialists
- Full-Service: Design → Permits → Build
- Free Property Eligibility Assessment
Can you build an ADU in the City of Rockville, MD?
City of Rockville ADU Guidelines
The rules that decide whether, and what, you can build. The table below carries the specifics.
Up to 75% of Your Home
Up to 75% of the main house's floor area · a detached ADU may be 600 sq ft when the house is under 800 sq ft · a basement ADU may fill the basement
Permitted by right
Permitted in R-400, R-200, R-150, R-90, R-75, R-60, R-40. No minimum lot size.
Accessory-Structure Setbacks
3 ft side and rear for a detached ADU up to 12 ft tall, rising to 12 ft for one 15–20 ft tall · max height 20 ft or the main house peak
Off-street spaces
No parking spaces required for an ADU
Owner must live on site
Owner must occupy the main house or the ADU at least six months a year · ADU and main house stay under common ownership · one rental license per property
Governing ordinance
City of Rockville Zoning Ordinance §25.6.3.6 and §25.8.1.3 (effective 1 August 2026)
Check Your Address
Run our free eligibility check and get the City of Rockville’s rules applied to your exact lot in about a minute.
Check my property →| Requirement | City of Rockville standard |
|---|---|
| Allowed by | Right, in permitted zones |
| Minimum lot size | No minimum |
| Permitted zones | R-400, R-200, R-150, R-90, R-75, R-60, R-40 |
| Maximum size | Up to 75% of the main house's floor area · a detached ADU may be 600 sq ft when the house is under 800 sq ft · a basement ADU may fill the basement |
| Setbacks | 3 ft side and rear for a detached ADU up to 12 ft tall, rising to 12 ft for one 15–20 ft tall · max height 20 ft or the main house peak |
| Parking | No parking spaces required for an ADU |
| Eligible homes | Detached single-family houses only — not townhouses, condominiums or apartments |
| Owner occupancy | Required |
| Garage or basement conversion | Allowed |
| Who may live there | Owner must occupy the main house or the ADU at least six months a year · ADU and main house stay under common ownership · one rental license per property |
| Ordinance | City of Rockville Zoning Ordinance §25.6.3.6 and §25.8.1.3 (effective 1 August 2026) |
| Rules current as of | 2026-08-01 |
Rockville sets its own zoning, separate from Montgomery County's, and the 2026 ordinance made the ADU a permitted use rather than a conditional one. If your lot has a single-family detached home, one ADU is allowed in any residential zone, and the old exclusion of R-40 lots is gone.
The size limit is now 75% of the main house's total floor area for attached and detached units alike. Two exceptions help smaller homes: an attached ADU in a basement may be as large as the basement, and a detached ADU may be up to 600 sq ft when the main house is under 800 sq ft. A detached unit follows the city's accessory-building setbacks, 3 feet from the side and rear lot lines for a building up to 12 feet tall, stepping up to 12 feet of setback for one 15 to 20 feet tall, with a 20-foot height cap or the peak of the main house, whichever is lower, on a permanent foundation. The ADU and the main house must stay under common ownership, with one rental license per property.
The City of Rockville ADU Permit Process
Makara ADU handles this entire process from design to move-in, full turn-key.
- 01
Zoning & Eligibility
Confirm the lot has a single-family detached home and calculate the 75% size limit from the house's floor area. Makara ADU does this free with our property eligibility checker.
- 02
Design & Drawings
Architectural and structural plans to the city's residential code, sized to the 75% limit and, for a detached unit, the accessory-building setbacks and 20-foot height cap.
- 03
ADU Application (City)
File the ADU application and plans with the City of Rockville through its MGO Connect portal, with the owner-occupancy and common-ownership conditions confirmed.
- 04
Building Permits & Build
Building and trades permits from the city; construction proceeds with city inspections along the way.
- 05
Final Inspection & Occupancy
The city's final inspection and occupancy approval, then keys in hand, ready to occupy or rent under the property's rental license.
City of Rockville’s ADU Specialists
We don't build everything. We build ADUs. Based in Gaithersburg, we work with local permitting offices every week and know how each jurisdiction's rules shape what can be built.
Local Rules, Known Cold
Every jurisdiction we serve has its own size limits, setbacks, parking and occupancy rules. We track them, and the eligibility checker on this page runs on that same data.
One Contractor, Start to Finish
Architecture, engineering, permits, foundation, framing, MEP, sprinklers, finishes, and the rental license — Makara ADU manages everything under one contract. No coordinating separate architects, engineers, and builders.
Fixed-Price Proposals
We quote your project in full before a shovel goes in the ground. No surprise change orders mid-construction — we plan for lot coverage, stormwater, and utility connections up front.
Built for Aging in Place & Family
Most of our City of Rockville clients build to keep aging parents or adult children close. We design single-floor, accessible units that work beautifully today and adapt gracefully over time.
ADU Types We Build in the City of Rockville
Most jurisdictions allow more than one ADU configuration. We help you choose the right one for your lot, your zone and your goals.
Detached Backyard Cottage
A fully independent structure in your backyard with its own entrance, kitchen and bath. The most flexible option, and the one most people picture. Size and placement follow the rules in the table above.
Attached Second Home
Add an attached ADU with its own separate entrance, kitchen, and bath. Makara ADU will collaborate with you to design the space to be functional to meet your needs while creating an aesthetically pleasing space that will add value to your life, family and your home.
Basement and Garage Conversions
Convert an existing garage or basement into a legal, licensed ADU — the most cost-effective path to added living space, and often faster to permit than new construction.
ADUs We’ve Built Recently
A sample of ADUs we’ve built across Montgomery County.
City of Rockville ADU FAQ
Is there a minimum lot size for an ADU in Rockville?
No. The ordinance does not set a minimum lot size. What matters is that the lot has a single-family detached home, the 75% size limit, and, for a detached unit, the accessory-building setbacks.
How big can an ADU be in Rockville?
Up to 75% of the main house's total floor area. A basement ADU may be as large as the basement, and a detached ADU may be up to 600 sq ft when the main house is under 800 sq ft.
Which zones allow an ADU?
Every residential zone: R-400, R-200, R-150, R-90, R-75, R-60 and R-40. In the mixed-use MXTD zones an ADU is a conditional use, allowed only beside a house that existed on August 1, 2026.
Is an ADU allowed by right?
Yes. Under the 2026 Zoning Ordinance an ADU is a permitted use in the residential zones, approved through the city's application and permit process rather than a conditional-use hearing.
Do I need extra parking for an ADU in Rockville?
No. The city does not require parking spaces for an ADU.
Can I rent out an ADU in Rockville?
Yes, subject to the city's rental licensing. Only one rental license is permitted per property, and the owner must occupy either the main house or the ADU for at least six months of the year.
Is Your City of Rockville Property Eligible for an ADU?
Use our free eligibility checker to find out in about a minute, and get a personalized report sent to your inbox.