A Frederick, Maryland mailing address does not tell you which ADU zoning code controls your property. Unincorporated Frederick County, the City of Frederick and the Town of Walkersville use different zoning frameworks, different approval paths and different 2026 transition rules. Applying the County’s 1,000-square-foot pathway or 6-foot accessory-structure rule to a City or Walkersville property can send a homeowner down the wrong permit path.
Jurisdiction warning
County, City and Town zoning are not interchangeable.
City of Frederick properties use the City Land Management Code and City permit system. Walkersville properties require Town zoning approval, while Frederick County generally handles the building permit and inspections. Unincorporated properties use Frederick County zoning.
Last verified: September 8, 2026. City of Frederick PC25-614ZTA and Walkersville Ordinance 2026-04 are transition items. Proposed language is identified as proposed and is not treated as enacted law.
1. Frederick County vs. Frederick City vs. Walkersville: quick comparison
| Issue | Unincorporated Frederick County | City of Frederick | Walkersville |
|---|---|---|---|
| 2026 status | 🟠 Active County system + streamlining transition | 🟠 Current 2021 ADU framework + PC25-614ZTA transition | 🟠 Draft Ordinance 2026-04; introduced Aug. 12, 2026, not verified as passed |
| Who controls zoning? | Frederick County | City of Frederick | Town of Walkersville |
| Building permit | Frederick County | City of Frederick | Frederick County after Town zoning certificate |
| Current / proposed size trigger | ≤1,000 sq ft permit path; larger ADUs special exception | Current FAQ: integrated ≤35% of primary floor area; detached ≤800 sq ft | Draft: up to 1,000 sq ft; ≤800 sq ft administrator review, 801–1,000 sq ft Planning Commission review |
| Owner occupancy | Current County framework requires owner occupancy | Current City framework requires owner in primary or ADU; 2026 amendment has debated changing this | Draft requires lot owner to occupy the primary dwelling |
| Parking | Current County rule: one additional space; on-street can count | Current City rule can require one additional space; 2026 amendment proposes changes | Draft: one off-street ADU space with a waiver path |
| Detached setback | General County accessory-structure screen includes 6 ft from lot line | Current City FAQ has its own new-detached formula; not the County 6-ft rule | Draft ties side/rear ADU setbacks to Town permanent-accessory-structure standards by zoning district |
Do not choose a column from the mailing address. Determine which government has zoning authority over the parcel first.
2. City of Frederick: an existing ADU program with its own rules
The City of Frederick already has a dedicated ADU framework under Land Management Code §802 and Ordinance G-21-15. The City’s current public ADU materials say ADUs are permitted in RO, R4, R6, R8, R12, R16, R20, DBO and DR residential districts and may be integrated into or placed as a separate structure on single-family, duplex and townhouse properties.
| Current City rule | Published treatment |
|---|---|
| Number of ADUs | One per lot. |
| Owner occupancy | Owner must live in either the primary residence or ADU. |
| Rental duration | Non-owner-occupied unit cannot be rented for less than 90 days. |
| Recorded restriction | Declaration of Restriction required. |
| Integrated ADU size | Current FAQ: no more than 35% of the primary residence floor area. |
| Detached ADU size | Current FAQ: no more than 800 sq ft. |
| New detached location | Current FAQ: rear yard only; current guidance says new detached ADUs are not permitted on lots with no rear yard. |
| New detached height | Current FAQ: maximum 25 ft or height of primary residence, whichever is less. |
The City also uses a setback formula that is materially different from the County’s 6-foot accessory-structure screen. The current City FAQ says a new detached ADU within 6 feet of the primary residence must meet the primary-residence setbacks; if it is more than 6 feet away, it must provide one-half of the primary-residence setback, but not less than 3 feet.
3. Frederick City’s 2026 ADU amendment: PC25-614ZTA
The City is actively reconsidering its ADU rules. Its 2025 Planning Department Annual Report identifies PC25-614ZTA — Section 802: Accessory Dwelling Units as a zoning text amendment intended to revise parking standards, owner-occupancy standards and the maximum allowable size of an ADU.
At the March 9, 2026 Planning Commission hearing, the Commission voted 4-0 to recommend approval of the draft amendments with additional recommendations for City Council consideration. The recommendations included no additional ADU parking in DB, DR and DBO even where parking is removed to create the ADU; retaining the owner-occupancy provision; and, if Council removes owner occupancy, considering a deed restriction or other protection against rapid investor conversion.
Why the City’s current size caps are a 2026 transition issue
Maryland Department of Planning says jurisdictions required to authorize ADUs consistent with HB 1466 may not limit ADU size below the state’s 75% definition. Frederick City’s currently published 35% integrated-unit cap and 800-square-foot detached cap therefore should not simply be assumed to be the City’s final post-HB-1466 size standards. PC25-614ZTA expressly identifies maximum allowable ADU size as an item being revised.
We do not declare the existing City caps automatically void. Until the City Council adopts replacement text or publishes an authoritative implementation position, homeowners should obtain the current written City interpretation before designing above the published limits. See our Maryland 75% ADU Size Guide for the statewide issue.
4. Walkersville: Draft Ordinance 2026-04 creates a very different pathway
Walkersville’s official Town Code page currently lists DRAFT ORDINANCE NO. 2026-04 — Accessory Dwelling Units. The draft itself states that it was introduced August 12, 2026, while the passage and approval dates remain blank. We therefore treat every substantive requirement below as draft / transition language, not final law.
The draft would authorize one ADU on a lot with an existing single-family detached dwelling. Its definition uses no more than 75% of the finished floor area above grade of the primary dwelling, but §B separately proposes a maximum ADU size of 1,000 square feet. That creates an important draft-text issue: on a primary dwelling larger than about 1,333 square feet, an absolute 1,000-square-foot cap could be lower than 75% of the primary dwelling. MDP’s FAQ says local jurisdictions may not cap ADU size below the 75% state definition. We therefore flag the 1,000-square-foot language for reconciliation before final passage rather than treating it as settled law.
| Walkersville draft provision | Proposed rule |
|---|---|
| Maximum size | Up to 1,000 sq ft, while also remaining within the draft 75% definition. |
| ≤800 sq ft | Planning & Zoning Administrator review. |
| 801–1,000 sq ft | Planning Commission approval. |
| Side/rear setback | Same as permanent accessory structures in the applicable Town zoning district. |
| Short-term rental | Prohibited by the draft. |
| Owner occupancy | Draft says the primary dwelling must be occupied by the lot owner. |
| Detached height | No taller than the primary dwelling. |
| Detached design | Same material standards, façade and roof design as the primary structure. |
| Existing nonconforming structure | May be converted but cannot be expanded or modified to increase the nonconformity. |
The draft also requires a clear unobstructed access path for emergency services, utility adequacy, a unique subaddress, and a zoning-certificate application that maps utilities, parking, setbacks, wells/septic where applicable and other site information.
5. Walkersville parking: the draft now has a waiver, but the study question remains
Walkersville’s April 14 Planning Commission minutes are important because staff expressly told the Commission that an ADU parking requirement could not be established until the state-required parking study was conducted. At that time, staff also said the Town did not yet have an established waiver process.
The August draft now proposes one off-street parking space per ADU and contains a waiver process when a space cannot reasonably be created because of space, orientation, topography or similar constraints. The draft allows on-street parking to satisfy the additional-space requirement when the waiver standard is met.
Track statewide parking-study research in our Maryland ADU Parking Rules & Parking Study Tracker.
6. Who actually issues the zoning approval and building permit?
| Property location | Zoning approval | Building permit / inspection |
|---|---|---|
| Unincorporated Frederick County | Frederick County | Frederick County |
| City of Frederick | City of Frederick | City of Frederick |
| Walkersville | Town of Walkersville zoning certificate first | Frederick County building, electrical and plumbing permit system |
Frederick County’s own permit page states that the City of Frederick issues its own building permits. Walkersville’s permit FAQ says the Town issues the zoning certificate and Frederick County issues building permits on behalf of the Town; the Town zoning certificate must be presented when applying for the County permit.
The Walkersville draft reinforces this split: ADUs would be constructed to Frederick County building-code requirements and would have to pass Frederick County inspection before occupancy, while the Town would issue the zoning certificate.
7. Downtown Frederick: Historic Preservation Overlay can add another approval layer
City of Frederick properties inside a Historic Preservation Overlay are subject to a separate exterior-review layer. The City says the Historic Preservation Commission must approve exterior work on designated properties, excluding qualifying minor rehabilitation.
For permit work that requires historic approval, the City’s permit guidance says the applicant must obtain an HPC Certificate of Approval before applying for the building/zoning permit. For an ADU, that can affect a new detached structure, rear addition, new entrance, windows, roof form, exterior materials and other changes.
8. The address illusion: how to avoid using the wrong ADU code
A postal address containing “Frederick, MD” does not prove the parcel is inside City limits. Likewise, a property physically in Frederick County can be inside Walkersville or another incorporated municipality with its own zoning authority.
- Confirm the actual municipal boundary. Do not use the ZIP code or mailing city as the zoning test.
- Identify the zoning authority. City of Frederick, Walkersville or Frederick County.
- Pull the zoning district from that government’s map/code.
- Use the correct ADU rule set. Do not copy size, setback or parking numbers from a neighboring jurisdiction.
- Confirm who issues the building permit. City of Frederick is self-permitting; Walkersville routes building permits through Frederick County.
- Re-check the 2026 transition status immediately before paying for plans.
For unincorporated properties, use our Frederick County ADU Rules 2026 deep dive. For side/rear placement, use the Maryland ADU Setback Rules lookup.
9. Bottom line
Frederick County, Frederick City and Walkersville are three different ADU zoning paths. The County’s 1,000-square-foot administrative threshold does not control inside the City. The City’s current 35%/800-square-foot framework does not control Walkersville. And Walkersville’s August 2026 draft cannot yet be treated as enacted law.
The first question for a Frederick-area homeowner is therefore not “How large can my ADU be?” It is “Which government has zoning authority over my parcel?”
Primary sources used for this municipal carve-out guide
- City of Frederick — Adding Accessory Dwelling Units
- City of Frederick — ADU FAQ / permit materials
- City of Frederick Planning Commission — March 9, 2026 minutes, PC25-614ZTA
- City of Frederick — Planning Department Annual Report / PC25-614ZTA description
- City of Frederick — pending/recent legislation
- City of Frederick — Historic Preservation Overlay
- Frederick County — municipal building-permit responsibility
- Town of Walkersville — Town Code / Draft Ordinance 2026-04 listing
- Town of Walkersville — Draft Ordinance 2026-04
- Walkersville Planning Commission — April 14, 2026 ADU workshop minutes
- Town of Walkersville — zoning certificate / County building permit FAQ
- Maryland Land Use §4-504 — local ADU requirements
Maryland ADU Guide is maintained by Gijo John as an independent research publication. We prioritize enacted law, official zoning materials, legislative records and permit guidance. Source-backed corrections can be sent to gijo.j@marylandaduguide.com.